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66 new articles

--  arXiv:1805.06894v1 [pdf, other] Score: Unrated
Kinematics of outer halo globular clusters: M 75 and NGC 6426
Comments: 9 pages, 9 figures, accepted for publication in Astronomy & Astrophysics

Globular clusters (GCs) and their dynamic interactions with the Galactic components provide an important insight into the structure and formation of the early Milky Way. Here, we present a kinematic study of two outer halo GCs based on a combination of VLT/FORS2, VLT/FLAMES, and Magellan/MIKE low- and high-resolution spectroscopy of 32 and 27 member stars, respectively. Although both clusters are located at Galactocentric distances of 15 kpc, they have otherwise very different properties. M 75 is a luminous and metal-rich system at [Fe/H] = $-1.2$ dex, a value that we confirm from the calcium triplet region. This GC shows mild evidence for rotation with an amplitude of A$_{\rm rot}\sim$5 km s$^{-1}$. One of the most metal-poor GCs in the Milky Way (at [FeII/H] = $-2.3$ dex), NGC 6426 exhibits marginal evidence of internal rotation at the 2 km s$^{-1}$ level. Both objects have velocity dispersions that are consistent with their luminosity. Although limited by small-number statistics, the resulting limits on their $A_{\rm rot}/\sigma_0$ ratios suggest that M 75 is a slow rotator driven by internal dynamics rather than being effected by the weak Galactic tides at its large distances. Here, M 75 ($A_{\rm rot}/\sigma=0.31$) is fully consistent with the properties of other, younger halo clusters. At $A_{\rm rot}/\sigma_0=0.8\pm0.4$, NGC 6426 appears to have a remarkably ordered internal motion for its low metallicity, but the large uncertainty does not allow for an unambiguous categorization as a fast rotator. An accretion origin of M 75 cannot be excluded, based on the eccentric orbit, which we derived from the recent data release 2 of Gaia, and considering its younger age.

--  arXiv:1805.06896v1 [pdf, other] Score: Unrated
The Formation of Ultra Diffuse Galaxies in Cored Dark Matter Halos Through Tidal Stripping and Heating
Comments: Submitted to MNRAS; comments welcome!

We propose that the Ultra-Diffuse Galaxy (UDG) population represents a set of satellite galaxies born in $\sim10^{10}-10^{11}~{\rm M_\odot}$ halos, similar to field dwarfs, which suffer a dramatic reduction in surface brightness due to tidal stripping and heating. This scenario is observationally motivated by the radial alignment of UDGs in Coma as well as the significant dependence of UDG abundance on cluster mass. As a test of this formation scenario, we apply a semi-analytic model describing the change in stellar mass and half-light radius of dwarf satellites, occupying either cored or cuspy halos, to cluster subhalos in the Bolshoi simulation. Key to this model are results from simulations which indicate that galaxies in cored dark-matter halos expand significantly in response to tidal stripping and heating, whereas galaxies in cuspy halos experience limited size evolution. Our analysis indicates that a population of tidally-stripped dwarf galaxies, residing in cored halos (like that of low-surface brightness field dwarfs), is able to reproduce the observed sizes, stellar masses, and abundance of UDGs in clusters remarkably well.

--  arXiv:1805.06897v1 [pdf, other] Score: Unrated
SNe Kicks in Hierarchical Triple Systems
Comments: 17 pages, 16 figures, 3 tables, submitted

Most massive stars, if not all, are in binary configuration or higher multiples. These massive stars undergo supernova explosions and end their lives as either black holes or neutron stars. Recent observations have suggested that neutron stars and perhaps even black holes receive large velocity kicks at birth. Such natal kicks and the sudden mass loss can significantly alter the orbital configuration of the system. Here we derive general analytical expressions that describe the effects of natal kicks in binaries on hierarchical triple systems. We explore several proof-of-concept applications such as black hole and neutron stars binaries and X-ray binaries with either stellar or Supermassive Black Hole (SMBH) companions on a wide orbit. Kicks can disrupt the hierarchical configuration, although it is harder to escape the potential well of an SMBH. Some binary systems do escape the SMBH system resulting in hyper-velocity binary system. Furthermore, kicks can result in increasing or decreasing the orbital separations. Decreasing the orbital separation may have significant consequences in these astrophysical systems. For example, shrinking the separation post-supernova kick can lead to the shrinking of an inner compact binary that then may merge via Gravitational Wave (GW) emission. This process yields a supernova that is shortly followed by a possible GW-LIGO event. Interestingly, we find that the natal kick can result in shrinking the outer orbit, and the binary may cross the tertiary Roche limit, breaking up the inner binary. Thus, in the case of SMBH companion, this process can lead to either a tidal disruption event or a GW-LISA detection event with a supernova precursor.

--  arXiv:1805.06898v1 [pdf, other] Score: Unrated
Gas-Assisted Growth of Protoplanets in a Turbulent Medium
Comments: 40 pages, 20 figures

Pebble accretion is a promising process for decreasing growth timescales of planetary cores, allowing gas giants to form at wide orbital separations. However, nebular turbulence can reduce the efficiency of this gas-assisted growth. We present an order of magnitude model of pebble accretion, which calculates the impact of turbulence on the average velocity of small bodies, the radius for binary capture, and the sizes of the small bodies that can be accreted. We also include the effect of turbulence on the particle scale height, which has been studied in previous works. We find that turbulence does not prevent rapid growth in the high-mass regime: the last doubling time to the critical mass to trigger runaway gas accretion ($M \sim 10 \, M_\oplus$) is well within the disk lifetime even for strong ($\alpha \gtrsim 10^{-2}$) turbulence. We find that while the growth timescale is quite sensitive to the local properties of the protoplanetary disk, over large regimes of parameter space large cores grow in less than the disk lifetime if appropriately-sized small bodies are present. Instead, the effects of turbulence are most pronounced for low planetary masses. For strong turbulence the growth timescale is longer than the gas disk lifetime until the core reaches masses $\gtrsim 10^{-2}-10^{-1} M_\oplus$. A "Flow Isolation Mass", at which binary capture ceases, emerges naturally from our model framework. We comment that the dependence of this mass on orbital separation is similar to the semi-major axis distribution of solar-system cores.

--  arXiv:1805.06901v1 [pdf, other] Score: Unrated
Gravitational Wave Signals from the First Massive Black Hole Seeds
Comments: Submitted to MNRAS-L. This version includes minor revisions after the first referee report. Further comments are welcome

Recent numerical simulations reveal that the isothermal collapse of pristine gas in atomic cooling haloes may result in stellar binaries of supermassive stars with $M_* \gtrsim 10^4\ \mathrm{M}_{\odot}$. For the first time, we compute the in-situ merger rate for such massive black hole remnants by combining their abundance and multiplicity estimates. For black holes with initial masses in the range $10^{4-6} \ \mathrm{M}_{\odot}$ merging at redshifts $z \gtrsim 15$ our optimistic model predicts that LISA should be able to detect 0.6 mergers per year. This rate of detection can be attributed, without confusion, to the in-situ mergers of seeds from the collapse of very massive stars. Equally, in the case where LISA observes no mergers from heavy seeds at $z \gtrsim 15$ we can constrain the combined number density, multiplicity, and coalesence times of these high-redshift systems. This letter proposes gravitational wave signatures as a means to constrain theoretical models and processes that govern the abundance of massive black hole seeds in the early Universe.

--  arXiv:1805.06902v1 [pdf, other] Score: Unrated
Cosmological simulations of black hole growth II: how (in)significant are merger events for fuelling nuclear activity?
Comments: 21 pages, 10 figures, submitted to MNRAS, homepage:

Which mechanism(s) are mainly driving nuclear activity in the centres of galaxies is a major unsettled question. In this study, we investigate the statistical relevance of galaxy mergers for fuelling gas onto the central few kpc of a galaxy, potentially resulting in an active galactic nucleus (AGN). To robustly address that, we employ large-scale cosmological hydrodynamic simulations from the Magneticum Pathfinder set, adopting state-of-the-art models for BH accretion and AGN feedback. Our simulations predict that for luminous AGN ($L_{\rm AGN} > 10^{45} L_{\rm bol}$) at $z = 2$, more than 50 per cent of their host galaxies have experienced a merger in the last 0.5Gyr. These high merger fractions, however, merely reflect the intrinsically high merger rates of massive galaxies at $z=2$, in which luminous AGN preferentially occur. Apart from that, our simulation predictions disprove that merger events are the statistically dominant fuelling mechanism for nuclear activity over a redshift range $z=0-2$: irrespective of AGN luminosity, less than 20 per cent of AGN hosts have undergone a recent merger, in agreement with a number of observational studies. The central ISM conditions required for inducing AGN activity can be, but are not necessarily caused by a merger. Despite the statistically minor relevance of mergers, at a given AGN luminosity and stellar mass, the merger rates of AGN hosts can be by up to three times higher than that of inactive galaxies. Such elevated merger rates still point towards an intrinsic connection between AGN activity and mergers, consistent with our traditional expectation.

--  arXiv:1805.06905v1 [pdf, other] Score: Unrated
A Theory for the Variation of Dust Attenuation Laws in Galaxies
Comments: Submitted to ApJ; Comments Welcome

In this paper, we provide a physical model for the origin of variations in the shapes and bump strengths of dust attenuation laws in galaxies by combining a large suite of cosmological "zoom-in" galaxy formation simulations with 3D Monte Carlo dust radiative transfer calculations. We model galaxies over 3 orders of magnitude in stellar mass, ranging from Milky Way like systems through massive galaxies at high-redshift. Critically, for these calculations we employ a constant underlying dust extinction law in all cases, and examine how the role of geometry and radiative transfer effects impact the resultant attenuation curves. Our main results follow. Despite our usage of a constant dust extinction curve, we find dramatic variations in the derived attenuation laws. The slopes of normalized attenuation laws depend primarily on the complexities of star-dust geometry. Increasing fractions of unobscured young stars flatten normalized curves, while increasing fractions of unobscured old stars steepen curves. Similar to the slopes of our model attenuation laws, we find dramatic variation in the 2175 Angstrom ultraviolet (UV) bump strength, including a subset of curves with little to no bump. These bump strengths are primarily influenced by the fraction of unobscured O and B stars in our model, with the impact of scattered light having only a secondary effect. Taken together, these results lead to a natural relationship between the attenuation curve slope and 2175 Angstrom bump strength. Finally, we apply these results to a 25 Mpc/h box cosmological hydrodynamic simulation in order to model the expected dispersion in attenuation laws at integer redshifts from z=0-6. A significant dispersion is expected at low redshifts, and decreases toward z=6. We provide tabulated results for the best fit median attenuation curve at all redshifts.

--  arXiv:1805.06907v1 [pdf, other] Score: Unrated
Type Ia supernovae have two physical width-luminosity relations and they favor sub-Chandrasekhar and direct collision models - II. Color evolution
Comments: The Monte Carlo radiation transfer code URILIGHT used for the numerical calculations is provided

While the width-luminosity relation among type Ia supernovae (slower is brighter) is one of the best studied properties of this type of events, its physical basis has not been identified convincingly. The 'luminosity' is known to be related to a clear physical quantity - the amount of $^{56}$Ni synthesised, but the 'width' has not been quantitatively linked yet to a physical time scale. In Paper I it was shown that the gamma-ray escape time $t_0$, which determines the long term evolution of the bolometric light curve, can be robustly inferred from observations, and its observed values span a narrow range of 30-45 days for the full range of observed $^{56}$Ni masses. In this paper we show that the recombination time of $^{56}$Fe and $^{56}$Co from doubly to singly ionized states causes the typical observed break in the color curve B-V due to a cliff in the mean opacities, and is a robust width measure of the light curve, which is insensitive to radiation transfer uncertainties. We show that a simple photospheric model can be used to calculate the recombination time to an accuracy of $\sim5$ days, allowing a quantitative understanding of the color WLR. The two physical times scales of the width luminosity relation are shown to be set by two (direction averaged and $^{56}$Ni weighted) column densities- the total column density which sets $t_0$ and the $^{56}$Ni column density which sets the recombination time. Central detonations of sub-$\rm M_{ch}$ WDs and direct WD collision models have gamma-ray escape times and recombination times which are consistent with observations across the luminosity range of type Ia's. Delayed detonation Chandrasekhar mass models have recombination times that are broadly consistent with observations, with tension at the bright end of the luminosity range and inconsistent gamma-ray escape times at the faint end.

--  arXiv:1805.06913v1 [pdf, other] Score: Unrated
Spectroscopic decomposition of the galaxy and halo of the cD galaxy NGC 3311
Comments: 13 pages, 7 figures, accepted for publication in MNRAS

Information on the star-formation histories of cD galaxies and their extended stellar haloes lie in their spectra. Therefore, to determine whether these structures evolved together or through a two-phase formation, we need to spectroscopically separate the light from each component. We present a pilot study to use BUDDI to fit and extract the spectra of the cD galaxy NGC 3311 and its halo in an Integral Field Spectroscopy datacube, and carry out a simple stellar populations analysis to study their star-formation histories. Using MUSE data, we were able to isolate the light of the galaxy and its halo throughout the datacube, giving spectra representing purely the light from each of these structures. The stellar populations analysis of the two components indicates that, in this case, the bulk of the stars in both the halo and the central galaxy are very old, but the halo is more metal poor and less $\alpha$-enriched than the galaxy. This result is consistent with the halo forming through the accretion of much smaller satellite galaxies with more extended star formation. It is noteworthy that the apparent gradients in age and metallicity indicators across the galaxy are entirely consistent with the radially-varying contributions of galaxy and halo components, which individually display no gradients. The success of this study is promising for its application to a larger sample of cD galaxies that are currently being observed by IFU surveys.

--  arXiv:1805.06916v1 [pdf, other] Score: Unrated
Morphology of AGN Emission Line Regions in SDSS-IV MaNGA Survey
Comments: 14 pages, 7 figures, and 1 table, accepted for publication in MNRAS

Extended narrow-line regions (NLRs) around active galactic nuclei (AGN) are shaped by the distribution of gas in the host galaxy and by the geometry of the circumnuclear obscuration, and thus they can be used to test the AGN unification model. In this work, we quantify the morphologies of the narrow-line regions in 308 nearby AGNs ($z=0-0.14$, \lbol $\sim 10^{42.4-44.1}$ \erg{}) from the MaNGA survey. Based on the narrow-line region maps, we find that a large fraction (81\%) of these AGN have bi-conical NLR morphology. The distribution of their measured opening angles suggests that the intrinsic opening angles of the ionization cones has a mean value of 85--98$^\circ$ with a finite spread of 39-44$^\circ$ (1-$\sigma$). Our inferred opening angle distribution implies a number ratio of type I to type II AGN of 1:1.6--2.3, consistent with other measurements of the type I / type II ratio at low AGN luminosities. Combining these measurements with the WISE photometry data, we find that redder mid-IR color (lower effective temperature of dust) corresponds to stronger and narrower photo-ionized bicones. This relation is in agreement with the unification model that suggests that the bi-conical narrow-line regions are shaped by a toroidal dusty structure within a few pc from the AGN. Furthermore, we find a significant alignment between the minor axis of host galaxy disks and AGN ionization cones. Together, these findings suggest that obscuration on both circumnuclear ($\sim $pc) and galactic ($\sim$ kpc) scales are important in shaping and orienting the AGN narrow-line regions.

--  arXiv:1805.06918v1 [pdf, other] Score: Unrated
C/2016 R2 (PANSTARRS): A comet rich in CO and depleted in HCN
Comments: 14 pages, 2 figures, 2 tables. Accepted for publication in The Astronomical Jorunal

We observed comet C/2016 R2 (PANSTARRS) with the ARO 10-m SMT, and report the first detection of CO emission from this comet with amounts high enough to be the primary driver of activity. We obtained spectra and maps of the CO J=2-1 rotational line at 230 GHz between 2017 December and 2018 January. We calculated an average production rate of Q(CO)=(4.6+/-0.4)x10$^{28}$ mol s$^{-1}$ at r ~2.9 au and delta ~2.1 au. The CO line is thin FWHM ~ 0.8 km s$^{-1}$ with a slight blue-shift ~ -0.1 km s$^{-1}$ from the ephemeris velocity, and we derive a gas expansion velocity of V$_{exp}$ = 0.50+/-0.15 km s$^{-1}$. This comet produced approximately half the CO that comet C/1995 O1 (Hale-Bopp) did at 3 au. If CO production scales with nucleus surface area, then the radius need not exceed ~15 km. The spectra and mapping data are consistent with CO arising from a combination of a sunward-side active area and an isotropic source. For HCN, we calculated a 3-sigma upper limit production rate of Q(HCN) < 8x10$^{24}$ molecules s$^{-1}$, which corresponds to an extraordinarily high abundance ratio limit of Q(CO)/Q(HCN) > 5000. We inferred a production rate of molecular nitrogen of Q(N$_2$) ~2.8x10$^{27}$ molecules s$^{-1}$ using our CO data and the reported N$_2$/CO column density ratio (Cochran & MacKay 2018a,b). The comet does not show the typical nitrogen depletion seen in comets, and the CO-rich, N$_2$-rich and HCN-depleted values are consistent with formation in a cold environment of T < 50 K that may have provided significant N$_2$ shielding.

--  arXiv:1805.06920v1 [pdf, other] Score: Unrated
A Mid-IR Selected Changing-Look Quasar and Physical Scenarios for Abrupt AGN Fading
Comments: 9 pages, 4 figures, submitted to MNRAS

We report a new changing-look quasar, WISE~J105203.55+151929.5 at $z=0.303$, found by identifying highly mid-IR variable quasars in the WISE/NEOWISE data stream. Compared to multi-epoch mid-IR photometry of a large sample of SDSS-confirmed quasars, WISE J1052+1519 is an extreme photometric outlier, fading by more than a factor of two at $3.4$ and $4.6 \mu$m since 2009. Swift target-of-opportunity observations in 2017 show even stronger fading in the soft X-rays compared to the ROSAT detection of this source in 1995, with at least a factor of fifteen decrease. We obtained second-epoch spectroscopy with the Palomar telescope in 2017 which, when compared with the 2006 archival SDSS spectrum, reveals that the broad H$\beta$ emission has vanished and that the quasar has become significantly redder. The two most likely interpretations for this dramatic change are source fading or obscuration, where the latter is strongly disfavored by the mid-IR data. We discuss various physical scenarios that could cause such changes in the quasar luminosity over this timescale, and favor changes in the innermost regions of the accretion disk that occur on the thermal and heating/cooling front timescales. We discuss possible physical triggers that could cause these changes, and predict the multiwavelength signatures that could distinguish these physical scenarios.

--  arXiv:1805.06921v1 [pdf, other] Score: Unrated
A new physical interpretation of optical and infrared variability in quasars
Comments: 13 pages, 4 figures, 2 tables. Submitted to MNRAS. Comments very much welcome. All code and data links on GitHub,

Changing-look quasars are a recently identified class of active galaxies in which the strong UV continuum and/or broad optical hydrogen emission lines associated with unobscured quasars either appear or disappear on timescales of months to years. The physical processes responsible for this behaviour are still debated, but changes in the black hole accretion rate or accretion disk structure appear more likely than changes in obscuration. Here we report on four epochs of spectroscopy of SDSS J110057.70-005304.5, a quasar at a redshift of $z=0.378$ whose UV continuum and broad hydrogen emission lines have faded, and then returned over the past $\approx$20 years. The change in this quasar was initially identified in the infrared, and an archival spectrum from 2010 shows an intermediate phase of the transition during which the flux below rest-frame $\approx$3400\AA\ has decreased by close to an order of magnitude. This combination is unique compared to previously published examples of changing-look quasars, and is best explained by dramatic changes in the innermost regions of the accretion disk. The optical continuum has been rising since mid-2016, leading to a prediction of a rise in hydrogen emission line flux in the next year. Increases in the infrared flux are beginning to follow, delayed by a $\sim$3 year observed timescale. If our model is confirmed, the physics of changing-look quasars are governed by processes at the innermost stable circular orbit (ISCO) around the black hole, and the structure of the innermost disk. The easily identifiable and monitored changing-look quasars would then provide a new probe and laboratory of the nuclear central engine.

--  arXiv:1805.06922v1 [pdf, other] Score: Unrated
Preparing the NIRSpec/JWST science data calibration: from ground testing to sky
Comments: To appear in the Proceedings of the SPIE (Space Telescopes and Instrumentation 2018)

The Near-Infrared Spectrograph (NIRSpec) is one of four instruments aboard the James Webb Space Telescope (JWST). NIRSpec is developed by ESA with AIRBUS Defence & Space as prime contractor. The calibration of its various observing modes is a fundamental step to achieve the mission science goals and provide users with the best quality data from early on in the mission. Extensive testing of NIRSpec on the ground, aided by a detailed model of the instrument, allow us to derive initial corrections for the foreseeable calibrations. We present a snapshot of the current calibration scheme that will be revisited once JWST is in orbit.

--  arXiv:1805.06933v1 [pdf, other] Score: Unrated
TDEM final report: Enhanced direct imaging exoplanet detection with astrometry mass determination
Comments: No comment found

This Final Report (FR) presents the results of the Enhanced direct imaging exoplanet detection with astrometry mass determination project, which was executed in support of NASA's Exoplanet Exploration Program and the ROSES Technology Development for Exoplanet Missions (TDEM). The first milestone is concerned with a demonstration of medium fidelity astrometry accuracy and the second milestone demonstrates high-contrast imaging utilizing the same astrometry-capable optics. We have met milestone #1 with a comfortable margin. The average accuracy obtained over the three datasets is 5.75e-5 L/D, which is 4 times better than the milestone requirement, or equivalent to 2.5microarcsec on 2.4m telescope, or 1.5microarcsec for a 4m telescope, working in the visible band. These results show the potential of this technique to enable detection and measure masses of Earth-like planets around nearby stars, hence bringing a real benefit to the astronomy community. We also met milestone #2 and demonstrated that it is possible to achieve high-contrast imaging utilizing a coronagraph fed by a telescope equipped with a DP, enabling dual use of the telescope. We performed three different high-contrast imaging runs and met the milestone #2 of 5e-7 raw contrast for all of them. On average, we obtained 3.33e-7 raw contrast considering all data sets. This result is 35% better than the milestone #2 requirement. We validated the stability of the high-contrast region by averaging frames and subtracting the average from single frames, which resulted in contrast improvement of approximately one order of magnitude, reaching 2.72e-8 contrast. The main achievement of this work was the medium fidelity demonstration and feasibility validation of performing astrometry and direct imaging using the same instrument, significantly enhancing the expected scientific yield of dedicated exoplanet characterization missions.

--  arXiv:1805.06934v1 [pdf, other] Score: Unrated
The case for a cold dark matter cusp in Draco
Comments: 18 pages, 11 Figures, submitted to MNRAS. Comments welcome!

We use a new mass modelling method, GravSphere, to measure the central dark matter density profile of the Draco dwarf spheroidal galaxy. Draco's star formation shut down long ago, making it a prime candidate for hosting a 'pristine' dark matter cusp, unaffected by stellar feedback during galaxy formation. We first test GravSphere on a suite of three tidally stripped mock 'Draco'-like dwarfs, placed on orbits similar to the real Draco around the Milky Way, containing realistic populations of binary stars, and with realistic foreground contamination. We show that we are able to correctly infer the dark matter density profile of both cusped and cored mocks within our 95% confidence intervals. While we obtain only a weak inference on the logarithmic slope of these density profiles, we are able to obtain a robust inference of the amplitude of the inner dark matter density at 150pc, $\rho_{\rm DM}(150\,{\rm pc})$. We show that, combined with constraints on the density profile at larger radii, this is sufficient to distinguish a $\Lambda$ Cold Dark Matter ($\Lambda$CDM) cusp $-$ that has $\rho_{\rm DM}(150\,{\rm pc}) > 1.8 \times 10^8\,{\rm M}_\odot \,{\rm kpc}^{-3}$ $-$ from alternative dark matter models that have lower inner densities. We then apply GravSphere to the real Draco data. We find that Draco has an inner dark matter density of $\rho_{\rm DM}(150\,{\rm pc}) = 2.4_{-0.6}^{+0.5} \times 10^8\,{\rm M}_\odot \,{\rm kpc}^{-3}$, consistent with a $\Lambda$CDM cusp. Using a velocity independent SIDM model, calibrated on $\Lambda$SIDM cosmological simulations, we show that Draco's high central density gives an upper bound on the SIDM cross section of $\sigma/m < 0.57\,{\rm cm}^2\,{\rm g}^{-1}$ at 99% confidence. We conclude that the inner density of nearby dwarf galaxies like Draco provides a new and competitive probe of dark matter models.

--  arXiv:1805.06938v1 [pdf, other] Score: Unrated
The impact of assembly bias on the halo occupation in hydrodynamical simulations
Comments: Submitted to MNRAS. 15 pages, 10 figures. Comments welcome

We investigate the variations in galaxy occupancy of the dark matter haloes with the large-scale environment and halo formation time, using two state-of-the-art hydrodynamical cosmological simulations, EAGLE and Illustris. For both simulations, we use three galaxy samples with a fixed number density ranked by stellar mass. For these samples we find that low-mass haloes in the most dense environments are more likely to host a central galaxy than those in the least dense environments. When splitting the halo population by formation time, these relations are stronger. Hence, at a fixed low halo mass, early-formed haloes are more likely to host a central galaxy than late-formed haloes since they have had more time to assemble. The satellite occupation shows a reverse trend where early-formed haloes host fewer satellites due to having more time to merge with the central galaxy. We also analyse the stellar mass -- halo mass relation for central galaxies in terms of the large-scale environment and formation time of the haloes. We find that low mass haloes in the most dense environment host relatively more massive central galaxies. This trend is also found when splitting the halo population by age, with early-formed haloes hosting more massive galaxies. Our results are in agreement with previous findings from semi-analytical models, providing robust predictions for the occupancy variation signature in the halo occupation distribution of galaxy formation models.

--  arXiv:1805.06941v1 [pdf, other] Score: Unrated
Scientific Discovery with the James Webb Space Telescope
Comments: Accepted for Publication in Contemporary Physics. 67 pages, including 18 figures. Astro-ph version includes an Appendix on "Observing Opportunities"

For the past 400 years, astronomers have sought to observe and interpret the Universe by building more powerful telescopes. These incredible instruments extend the capabilities of one of our most important senses, sight, towards new limits such as increased sensitivity and resolution, new dimensions such as exploration of wavelengths across the full electromagnetic spectrum, new information content such as analysis through spectroscopy, and new cadences such as rapid time-series views of the variable sky. The results from these investments, from small to large telescopes on the ground and in space, have completely transformed our understanding of the Universe; including the discovery that Earth is not the center of the Universe, that the Milky Way is one among many galaxies in the Universe, that relic cosmic background radiation fills all space in the early Universe, that that the expansion rate of the Universe is accelerating, that exoplanets are common around stars, that gravitational waves exist, and much more. For modern astronomical research, the next wave of breakthroughs in fields ranging over planetary, stellar, galactic, and extragalactic science motivate a general-purpose observatory that is optimized at near- and mid-infrared wavelengths, and that has much greater sensitivity, resolution, and spectroscopic multiplexing than all previous telescopes. This scientific vision, from measuring the composition of rocky worlds in the nearby Milky Way galaxy to finding the first sources of light in the Universe to other topics at the forefront of modern astrophysics, motivates the state-of-the-art James Webb Space Telescope (Webb). In this review paper, I summarize the design and technical capabilities of Webb and the scientific opportunities that it enables.

--  arXiv:1805.06943v1 [pdf, other] Score: Unrated
Long Term Planetary Habitability and the Carbonate-Silicate Cycle
Comments: 31 pages, 5 figures, 1 table. Accepted for publication in Astrobiology

The potential habitability of an exoplanet is traditionally assessed by determining if its orbit falls within the circumstellar `habitable zone' of its star, defined as the distance at which water could be liquid on the surface of a planet (Kopparapu et al., 2013). Traditionally, these limits are determined by radiative-convective climate models, which are used to predict surface temperatures at user-specified levels of greenhouse gases. This approach ignores the vital question of the (bio)geochemical plausibility of the proposed chemical abundances. Carbon dioxide is the most important greenhouse gas in Earth's atmosphere in terms of regulating planetary temperature, with the long term concentration controlled by the balance between volcanic outgassing and the sequestration of CO2 via chemical weathering and sedimentation, as modulated by ocean chemistry, circulation and biological (microbial) productivity. We develop a model incorporating key aspects of Earth's short and long-term biogeochemical carbon cycle to explore the potential changes in the CO2 greenhouse due to variance in planet size and stellar insolation. We find that proposed changes in global topography, tectonics, and the hydrological cycle on larger planets results in proportionally greater surface temperatures for a given incident flux. For planets between 0.5 to 2 R_earth the effect of these changes results in average global surface temperature deviations of up to 20 K, which suggests that these relationships must be considered in future studies of planetary habitability.

--  arXiv:1805.06957v1 [pdf, other] Score: Unrated
Signatures of the disk-jet coupling in the Broad-line Radio Quasar 4C+74.26
Comments: 9 pages and 6 figures, ApJ submitted

Here we explore the disk-jet connection in the broad-line radio quasar 4C+74.26, utilizing the results of the multiwavelength monitoring of the source. The target is unique in that its radiative output at radio wavelengths is dominated by a moderately-beamed nuclear jet, at optical frequencies by the accretion disk, and in the hard X-ray range by the disk corona. Our analysis reveals a correlation (local and global significance of 96\% and 98\%, respectively) between the optical and radio bands, with the disk lagging behind the jet by $250 \pm 42$ days. We discuss the possible explanation for this, speculating that the observed disk and the jet flux changes are generated by magnetic fluctuations originating within the innermost parts of a truncated disk, and that the lag is related to a delayed radiative response of the disk when compared with the propagation timescale of magnetic perturbations along relativistic outflow. This scenario is supported by the re-analysis of the NuSTAR data, modelled in terms of a relativistic reflection from the disk illuminated by the coronal emission, which returns the inner disk radius $R_{\rm in}/R_{\rm ISCO} =35^{+40}_{-16}$. We discuss the global energetics in the system, arguing that while the accretion proceeds at the Eddington rate, with the accretion-related bolometric luminosity $L_{\rm bol} \sim 9 \times 10^{46}$ erg s$^{-1}$ $\sim 0.2 L_{\rm Edd}$, the jet total kinetic energy $L_\textrm{j} \sim 4 \times 10^{44}$ erg s$^{-1}$, inferred from the dynamical modelling of the giant radio lobes in the source, constitutes only a small fraction of the available accretion power.

--  arXiv:1805.06961v1 [pdf, other] Score: Unrated
Luminous WISE-selected Obscured, Unobscured, and Red Quasars in Stripe 82
Comments: Accepted for publication in ApJ; 35 pages, 22 Figures, 8 Tables

We present a spectroscopically complete sample of 147 infrared-color-selected AGN down to a 22 $\mu$m flux limit of 20 mJy over the $\sim$270 deg$^2$ of the SDSS Stripe 82 region. Most of these sources are in the QSO luminosity regime ($L_{\rm bol} \gtrsim 10^{12} L_\odot$) and are found out to $z\simeq3$. We classify the AGN into three types, finding: 57 blue, unobscured Type-1 (broad-lined) sources; 69 obscured, Type-2 (narrow-lined) sources; and 21 moderately-reddened Type-1 sources (broad-lined and $E(B-V) > 0.25$). We study a subset of this sample in X-rays and analyze their obscuration to find that our spectroscopic classifications are in broad agreement with low, moderate, and large amounts of absorption for Type-1, red Type-1 and Type-2 AGN, respectively. We also investigate how their X-ray luminosities correlate with other known bolometric luminosity indicators such as [O III] line luminosity ($L_{\rm [OIII]}$) and infrared luminosity ($L_{6 \mu{\rm m}}$). While the X-ray correlation with $L_{\rm [OIII]}$ is consistent with previous findings, the most infrared-luminous sources appear to deviate from established relations such that they are either under-luminous in X-rays or over-luminous in the infrared. Finally, we examine the luminosity function (LF) evolution of our sample, and by AGN type, in combination with the complementary, infrared-selected, AGN sample of Lacy et al. (2013), spanning over two orders of magnitude in luminosity. We find that the two obscured populations evolve differently, with reddened Type-1 AGN dominating the obscured AGN fraction ($\sim$30%) for $L_{5 \mu{\rm m}} > 10^{45}$ erg s$^{-1}$, while the fraction of Type-2 AGN with $L_{5 \mu{\rm m}} < 10^{45}$ erg s$^{-1}$ rises sharply from 40% to 80% of the overall AGN population.

--  arXiv:1805.06973v1 [pdf, other] Score: Unrated
Winds of Massive Stars: High Resolution X-ray Spectra of Stars in NGC 3603
Comments: Submitted for publication in AAS Journals

The cluster NGC 3603 hosts some of the most massive stars in the Galaxy. With a modest 50 ks exposure with the Chandra High Energy Grating Spectrometer, we have resolved emission lines in spectra of several of the brightest cluster members which are of WNh and O spectral types. This observation provides our first definitive high-resolution spectra of such stars in this nearby starburst region. The stars studied have broadened X-ray emission lines, some with blue-shifted centroids, and are characteristic of massive stellar winds with terminal velocities around 2000--3000 km/s. X-ray luminosities and plasma temperatures are very high for both the WNh and O stars studied. We conclude that their X-rays are likely the result of colliding winds.

--  arXiv:1805.06974v1 [pdf, other] Score: Unrated
On the Nature of Long-Period Dwarf Novae with Rare and Low-Amplitude Outbursts
Comments: 17 pages, 18 figures, 2 tables with supporting information. Accepted for publication in PASJ

There are several peculiar long-period dwarf-nova like objects, which show rare, low-amplitude outbursts with highly ionized emission lines. 1SWASP J162117$+$441254, BD Pav, and V364 Lib belong to this kind of objects. Some researchers even doubt whether 1SWASP J1621 and V364 Lib have the same nature as normal dwarf novae. We studied the peculiar outbursts in these three objects via our optical photometry and spectroscopy, and performed numerical modeling of their orbital variations to investigate their properties. We found that their outbursts lasted for a long interval (a few tens of days), and that slow rises in brightness were commonly observed during the early stage of their outbursts. Our analyses and numerical modeling suggest that 1SWASP J1621 has a very high inclination, close to 90 deg, plus a faint hot spot. Although BD Pav seems to have a slightly lower inclination ($\sim$75 deg), the other properties are similar to those in 1SWASP J1621. On the other hand, V364 Lib appears to have a massive white dwarf, a hot companion star, and a low inclination ($\sim$35 deg). In addition, these three objects possibly have low transfer rate and/or large disks originating from the long orbital periods. We find that these properties of the three objects can explain their infrequent and low-amplitude outbursts within the context of the disk instability model in normal dwarf novae without strong magnetic field. In addition, we suggest that the highly-ionized emission lines in outburst are observed due to a high inclination and/or a massive white dwarf. More instances of this class of object may be unrecognized, since their unremarkable outbursts can be easily overlooked.

--  arXiv:1805.06976v1 [pdf, other] Score: Unrated
Cosmological cluster tension
Comments: 4 pages, 3 figures, Proceedings of the 53rd Rencontres de Moriond: Cosmology (2018)

The abundance of clusters is a classical cosmological probe sensitive to both the geometrical aspects and the growth rate of structures. The abundance of clusters of galaxies measured by Planck has been found to be in tension with the prediction of the LCDM models normalized to Planck CMB fluctuations power spectra. The same tension appears with X-ray cluster local abundance. Massive neutrinos and modified gravity are two possible solutions to fix this tension. Alternatively, others options include a bias in the selection procedure or in the mass calibration of clusters. We present a study, based on our recent work, updating the present situation on this topic and discuss the likelihood of the various options.

--  arXiv:1805.06984v1 [pdf, other] Score: Unrated
Forward modelling of quasar light curves and the cosmological matter power spectrum on milliparsec scales
Comments: No comment found

We devise an optimal method to measure the temporal power spectrum of the lensing and intrinsic fluctuations of multiply-imaged strongly lensed quasar light curves, along with the associated time delays. The method is based on a Monte-Carlo Markov Chain (MCMC) sampling of a putative gaussian likelihood, and accurately recovers the input properties of simulated light curves, as well as the "Time Delay Challenge". We apply this method to constrain the dimensionless cosmological (non-linear) matter power spectrum on milliparsec scales (comparable to the size of the solar system), to $\Delta_{\rm NL}^4< 1 \times 10^7$ at $k_{\rm NL} \sim 10^3 {\rm pc}^{-1}$. Using a semi-analytic nonlinear clustering model which is calibrated to simulations, the corresponding constraint on the primordial (linear) scalar power spectrum is ${\cal P}_{\cal R} < 3 \times 10^{-9}$ at $k_{\rm L}\sim$ 3 pc$^{-1}$. This is the strongest constraint on primordial power spectrum at these scales, and is within an order of magnitude from the standard $\Lambda$CDM prediction. We also report measurements of temporal spectra for intrinsic variabilities of quasar light curves, which can be used to constrain the size of the emitting region in accretion disks. Future cadenced optical imaging surveys, such as LSST, should increase the number of observed strongly lensed quasars by 3 orders of magnitude and significantly improve these measurements, even though improvements in modelling quasar accretion and stellar microlensing are necessary.

--  arXiv:1805.07007v1 [pdf, other] Score: Unrated
Exploring possible relations between optical variability time scales and broad emission line shapes in AGN
Comments: 13 pages, 3 figures, Accepted on 11 May 2018 Front. Astron. Space Sci

Here we investigate the connection of broad emission line shapes and continuum light curve variability time scales of type-1 Active Galactic Nuclei (AGN). We developed a new model to describe optical broad emission lines as an accretion disk model of a line profile with additional ring emission. We connect ring radii with orbital time scales derived from optical light curves, and using Kepler's third law, we calculate mass of central supermassive black hole (SMBH). The obtained results for central black hole masses are in a good agreement with {other methods. This indicates that the variability time scales of AGN may not be stochastic, but rather connected to the orbital time scales which depend on the central SMBH mass.

--  arXiv:1805.07016v1 [pdf, other] Score: Unrated
VLT/X-shooter GRBs: Individual extinction curves of star-forming regions
Comments: 4 Figures, 2 Tables, MNRAS accepted

The extinction profiles in Gamma-Ray Burst (GRB) afterglow spectral energy distributions (SEDs) are usually described by the Small Magellanic Cloud (SMC)-type extinction curve. In different empirical extinction laws, the total-to-selective extinction, RV, is an important quantity because of its relation to dust grain sizes and compositions. We here analyse a sample of 17 GRBs (0.34<z<7.84) where the ultraviolet to near-infrared spectroscopic observations are available through the VLT/X-shooter instrument, giving us an opportunity to fit individual extinction curves of GRBs for the first time. Our sample is compiled on the basis that multi-band photometry is available around the X-shooter observations. The X-shooter data are combined with the Swift X-ray data and a single or broken power-law together with a parametric extinction law is used to model the individual SEDs. We find 10 cases with significant dust, where the derived extinction, AV, ranges from 0.1-1.0mag. In four of those, the inferred extinction curves are consistent with the SMC curve. The GRB individual extinction curves have a flat RV distribution with an optimal weighted combined value of RV = 2.61+/-0.08 (for seven broad coverage cases). The 'average GRB extinction curve' is similar to, but slightly steeper than the typical SMC, and consistent with the SMC Bar extinction curve at ~95% confidence level. The resultant steeper extinction curves imply populations of small grains, where large dust grains may be destroyed due to GRB activity. Another possibility could be that young age and/or lower metallicities of GRBs environments are responsible for the steeper curves.

--  arXiv:1805.07026v1 [pdf, other] Score: Unrated
The growth of stellar mass black hole binaries trapped in an accretion disk of active galactic nuclei
Comments: Accepted for publication in ApJL

Among the four black hole binary merger events detected by LIGO, six progenitor black holes have masses greater than 20\,$M_\odot$. The existence of such massive BHs calls for extreme metal-poor stars as the progenitors. An alternative possibility that a pair of stellar mass black holes each with mass $\sim7\,M_\odot$ increases to $>20\,M_\odot$ via accretion from a disk surrounding a super massive black hole in an active galactic nucleus is considered. The growth of mass of the binary and the transfer of orbital angular momentum to the disk accelerates the merger. Based on the recent numerical work of Tang et al. (2017), it is found that, in the disk of a low mass AGN with mass $\sim10^6\,M_\odot$ and Eddington ratio $>0.01$, the mass of an individual BH in the binary can grow to $>20\,M_\odot$ before coalescence provided that accretion takes place at a rate more than 10 times the Eddington value. The mechanism predicts a new class of gravitational wave sources involving the merger of two extreme Kerr black holes associated with active galactic nuclei and a possible electromagnetic wave counterpart.

--  arXiv:1805.07032v1 [pdf, other] Score: Unrated
Solar cycle observations of the Neon abundance in the Sun-as-a-star
Comments: To be published in The Astrophysical Journal. Figure 1 is reduced resolution to meet size limits

Properties of the Sun's interior can be determined accurately from helioseismological measurements of solar oscillations. These measurements, however, are in conflict with photospheric elemental abundances derived using 3-D hydrodynamic models of the solar atmosphere. This divergence of theory and helioseismology is known as the $"$solar modeling problem$"$. One possible solution is that the photospheric neon abundance, which is deduced indirectly by combining the coronal Ne/O ratio with the photospheric O abundance, is larger than generally accepted. There is some support for this idea from observations of cool stars. The Ne/O abundance ratio has also been found to vary with the solar cycle in the slowest solar wind streams and coronal streamers, and the variation from solar maximum to minimum in streamers ($\sim$0.1 to 0.25) is large enough to potentially bring some of the solar models into agreement with the seismic data. Here we use daily-sampled observations from the EUV Variability Experiment (EVE) on the Solar Dynamics Observatory taken in 2010--2014, to investigate whether the coronal Ne/O abundance ratio shows a variation with the solar cycle when the Sun is viewed as a star. We find only a weak dependence on, and moderate anti-correlation with, the solar cycle with the ratio measured around 0.2--0.3 MK falling from 0.17 at solar minimum to 0.11 at solar maximum. The effect is amplified at higher temperatures (0.3--0.6 MK) with a stronger anti-correlation and the ratio falling from 0.16 at solar minimum to 0.08 at solar maximum. The values we find at solar minimum are too low to solve the solar modeling problem.

--  arXiv:1805.07044v1 [pdf, other] Score: Unrated
Reliability of stellar inclination estimated from asteroseismology: analytical criteria, mock simulations and Kepler data analysis
Comments: 17 pages, 10 figures, 3 tables, accepted for publication in MNRAS

Advances in asteroseismology of solar-like stars, now provide a unique method to estimate the stellar inclination $i_{\star}$. This enables to evaluate the spin-orbit angle of transiting planetary systems, in a complementary fashion to the Rossiter-McLaughlin effect, a well-established method to estimate the projected spin-orbit angle $\lambda$. Although the asteroseismic method has been broadly applied to the Kepler data, its reliability has yet to be assessed intensively. In this work, we evaluate the accuracy of $i_{\star}$ from asteroseismology of solar-like stars using 3000 simulated power spectra. We find that the low signal-to-noise ratio of the power spectra induces a systematic under-estimate (over-estimate) bias for stars with high (low) inclinations. We derive analytical criteria for the reliable asteroseismic estimate, which indicates that reliable measurements are possible in the range of $20^\circ \lesssim i_{\star} \lesssim 80^\circ$ only for stars with high signal-to-noise ratio. We also analyse and measure the stellar inclination of 94 Kepler main-sequence solar-like stars, among which 33 are planetary hosts. According to our reliability criteria, a third of them (9 with planets, 22 without) have accurate stellar inclination. Comparison of our asteroseismic estimate of $v\sin{i_{\star}}$ against spectroscopic measurements indicates that the latter suffers from a large uncertainty possibly due to the modeling of macro-turbulence, especially for stars with projected rotation speed $v\sin{i_{\star}} \lesssim 5$ km/s. This reinforces earlier claims, and the stellar inclination estimated from the combination of measurements from spectroscopy and photometric variation for slowly rotating stars needs to be interpreted with caution.

--  arXiv:1805.07062v1 [pdf, other] Score: Unrated
The distribution and physical properties of high-redshift [OIII] emitters in a cosmological hydrodynamics simulation
Comments: 5 pages, 4 figures

Recent observations with the Atacama Large Millimeter/submillimeter Array (ALMA) detected far-infrared emission lines such as the [OIII] 88 \mu m line from galaxies at $z \sim 7 - 9$. Far-infrared lines can be used to probe the structure and kinematics of such high-redshift galaxies as well as to accurately determine their spectroscopic redshifts. We use a cosmological simulation of galaxy formation to study the physical properties of [OIII] 88 \mu m emitters. In a comoving volume of 50 $h^{-1}$ Mpc on a side, we locate 34 galaxies with stellar masses greater than $10^8\ {\rm M_\odot}$ at $z = 9$, and more than 270 such galaxies at $z = 7$. We calculate the [OIII] 88 \mu m luminosities ($L_{\rm OIII}$) by combining a physical model of HII regions with emission line calculations using the photoionization code CLOUDY. We show that the resulting $L_{\rm OIII}$, for a given star formation rate, is slightly higher than predicted from the empirical relation for local galaxies, and is consistent with recent observations of galaxies at redshifts 7 - 9. Bright [OIII] emitters with $L_{\rm OIII} > 10^8 {\rm L_\odot}$ have stellar masses greater than $10^9\ {\rm M_\odot}$, star formation rates higher than $3\ {\rm M_\odot\ yr}^{-1}$, and the typical metallicity is $\sim 0.1\ {\rm Z_\odot}$. The galaxies are hosted by dark matter halos with masses greater than $10^{10.5}\ {\rm M_\odot}$. Massive galaxies show characteristic structure where the [OIII] emitting gas largely overlaps with young stars, but the emission peak is separated from the main stellar population, suggesting the stochastic and localized nature of star formation in the first galaxies. We propose to use the [OIII] 5007 \AA\ line, to be detected by James Webb Space Telescope (JWST), to study the properties of galaxies whose [OIII] 88 \mu m line emission has been already detected with ALMA.

--  arXiv:1805.07065v1 [pdf, other] Score: Unrated
Discovery of deep eclipses in the cataclysmic variable IPHAS J051814.33+294113.0
Comments: 11 pages, 8 figures, accepted for publication in Astrophysics and Space Science

Performing the photometric observations of the cataclysmic variable IPHAS J051814.33+294113.0, we discovered very deep eclipses. The observations were obtained over 14 nights, had a total duration of 56 hours and covered one year. The large time span, during which we observed the eclipses, allowed us to measure the orbital period in IPHAS J051814.33+294113.0 with high precision, Porb=0.20603098+/-0.00000025 d. The prominent parts of the eclipses lasted 0.1+/-0.01 phases or 30+/-3 min. The depth of the eclipses was variable in the range 1.8-2.9 mag. The average eclipse depth was equal to 2.42+/-0.06 mag. The prominent parts of the eclipses revealed a smooth and symmetric shape. We derived the eclipse ephemeris, which, according to the precision of the orbital period, has a formal validity time of 500 years. This ephemeris can be useful for future investigations of the long-term period changes. During the latter four observational nights in 2017 January, we observed the sharp brightness decrease of IPHAS J051814.33+294113.0 by 2.3 mag. This brightness decrease imitated the end of the dwarf nova outburst. However, the long-term light curve of IPHAS J051814.33+294113.0 obtained in the course of the Catalina Sky Survey during 8 years showed no dwarf nova outbursts. From this we conclude that IPHAS J051814.33+294113.0 is a novalike variable. Moreover, the sharp brightness decrease, which we observed in IPHAS J051814.33+294113.0, suggests that this novalike variable belongs to the VY Scl-subtype. Due to very deep eclipses, IPHAS J051814.33+294113.0 is suitable to study the accretion disc structure using eclipse mapping techniques. Because this novalike variable has the long orbital period, it is of interest to determine the masses of the stellar components from radial velocity measurements. Then, our precise eclipse ephemeris can be useful to the phasing of spectroscopic data.

--  arXiv:1805.07073v1 [pdf, other] Score: Unrated
Which evolutionary status does the Blue Large-Amplitude Pulsators stay at?
Comments: 7 pages, 5 Figires, 1 table

Asteroseismology is a very useful tool for exploring the stellar interiors and evolutionary status and for determining stellar fundamental parameters, such as stellar mass, radius, surface gravity, and the stellar mean density. In the present work, we use it to preliminarily analyze the 14 new-type pulsating stars: Blue Large-Amplitude Pulsators (BLAPs) which is observed by OGLE project, to roughly analyze their evolutionary status. We adopt the theory of single star evolution and artificially set the mass loss rate of $\dot{M}=-2\times10^{-4}~{\rm M_{\odot}/year}$ and mass loss beginning at the radius of $R=40$ $\rm R_{\odot}$ on red giant branch to generate a series of theoretical models. Based on these theoretical models and the corresponding observations, we find that those BLAP stars are more likely to be the core helium burning stars. Most of them are in the middle and late phase of the helium burning.

--  arXiv:1805.07077v1 [pdf, other] Score: Unrated
The Gaia-ESO Survey: properties of newly discovered Li-rich giants
Comments: accepted for publication in A&A

We report 20 new lithium-rich giants discovered within the Gaia-ESO Survey, including the first Li-rich giant with evolutionary stage confirmed by CoRoT data. Atmospheric parameters and abundances were derived in model atmosphere analyses using medium-resolution GIRAFFE or high-resolution UVES spectra. These results are part of the fifth internal data release of Gaia-ESO. The Li abundances were corrected for non-LTE effects. We used Gaia DR2 parallaxes to estimate distances and luminosities. The giants have A(Li) > 2.2 dex. The majority of them (14 out of 20 stars) are in the CoRoT fields. Four giants are located in the field of three open clusters but are not members. Two giants were observed in fields towards the Galactic bulge but are likely in the inner disk. One of the bulge field giants is super Li-rich with A(Li) = 4.0 dex. We identified one giant with infrared excess at 22 microns. Two other giants, with large vsin i, might be Li-rich because of planet engulfment. Another giant is found to be barium enhanced and thus could have accreted material from a former AGB companion. Otherwise, besides the Li enrichment, the evolutionary stages are the only other connection between these new Li-rich giants. The CoRoT data confirm that one Li-rich giant is at the core-He burning stage. The other giants are concentrated in close proximity to the RGB luminosity bump, the core-He burning stages, or the early-AGB. This is very clear when looking at the Gaia-based luminosities of the Li-rich giants. This is also seen when the CoRoT Li-rich giants are compared to a larger sample of 2252 giants observed in the CoRoT fields by the Gaia-ESO Survey, which are distributed all over the RGB in the Teff-logg diagram. These observations show that evolutionary stage is a major factor behind the Li enrichment in giants. Other processes, like planet accretion, contribute to a smaller scale. [abridged]

--  arXiv:1805.07082v1 [pdf, other] Score: Unrated
The Excess Density of Field Galaxies near z=0.56 around the Gamma-Ray Burst GRB021004 Position
Comments: 23 pages, 13 figures

We study the clustering of field galaxies in the GRB021004 line of sight. The first signature is the GRB021004 field photometric redshifts distribution based on observations gathered at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, from which we infer a peak near z=0.56 estimated from multicolor photometry in the GRB direction. The second signature is the Mg II?? 2796, 2803 AA absorption doublet at z=0.56 in VLT/UVES spectra obtained for the GRB021004 afterglow. The third signature is the galaxy clustering in a larger (of about 3 square degrees) area around GRB021004 with an effective peak near z=0.56 obtained for both the spectral and photometric redshifts from a few catalogs of clusters based on the Sloan Digital Sky Survey (SDSS) and Baryon Oscillation Spectroscopic Survey (BOSS) as a part of SDSS-III. Using the data from the catalogs, the size of the whole inhomogeneity in distribution of the galaxy cluster with the peak near z=0.56 is also estimated as about 6-8 degrees or 140-190 Mpc. A possibility of inhomogeneity (a galaxy cluster) near the GRB021004 direction can be also confirmed by an inhomogeneity in the cosmic microwave background related with the Sunyaev-Zeldovich effect.

--  arXiv:1805.07089v1 [pdf, other] Score: Unrated
Automatic vetting of planet candidates from ground based surveys: Machine learning with NGTS
Comments: Accepted for publication in MNRAS, 15 pages

State of the art exoplanet transit surveys are producing ever increasing quantities of data. To make the best use of this resource, in detecting interesting planetary systems or in determining accurate planetary population statistics, requires new automated methods. Here we describe a machine learning algorithm that forms an integral part of the pipeline for the NGTS transit survey, demonstrating the efficacy of machine learning in selecting planetary candidates from multi-night ground based survey data. Our method uses a combination of random forests and self-organising-maps to rank planetary candidates, achieving an AUC score of 97.6\% in ranking 12368 injected planets against 27496 false positives in the NGTS data. We build on past examples by using injected transit signals to form a training set, a necessary development for applying similar methods to upcoming surveys. We also make the \texttt{autovet} code used to implement the algorithm publicly accessible. \texttt{autovet} is designed to perform machine learned vetting of planetary candidates, and can utilise a variety of methods. The apparent robustness of machine learning techniques, whether on space-based or the qualitatively different ground-based data, highlights their importance to future surveys such as TESS and PLATO and the need to better understand their advantages and pitfalls in an exoplanetary context.

--  arXiv:1805.07094v1 [pdf, other] Score: Unrated
Impact degassing and atmospheric erosion on Venus, Earth, and Mars during the late accretion
Comments: 31 pages, 12 Figures, accepted for publication in Icarus

The atmospheres of the terrestrial planets are known to have been modified as a consequence of the impact degassing and atmospheric erosion during the late accretion. Despite the commonality of these processes, there are distinct gaps -- roughly two orders of magnitude -- between the abundances of noble gases and nitrogen in the present-day atmospheres on Venus, Earth, and Mars. The element partitioning on planetary surfaces is thought to be significantly different between the three planets ~4 Ga: the runaway greenhouse on Venus, the carbon-silicate cycle and ocean formation on Earth, and the CO2-ice and H2O-ice formation on Mars. Consequences of element partitioning for the atmospheric evolution during the late accretion onto Venus, Earth, and Mars are investigated with a numerical model. We set upper limits to the partial pressures of CO2 and H2O on Earth and Mars, which corresponds to the state of phase equilibrium and carbon-silicate cycle. The final N2 mass shrinks by ~40% and ~15% for Earth and Mars, respectively. The effect of element partitioning is found to be insufficient to reproduce the gaps. For Venus, the survival of the primordial atmosphere through the late accretion may partially account for the present-day atmosphere. Whereas on Mars, the atmospheric escape due to solar extreme UV and wind may have also influenced the atmospheric evolution.

--  arXiv:1805.07100v1 [pdf, other] Score: Unrated
KIC 3240411 - the hottest known SPB star with the asymptotic g-mode period spacing
Comments: publisched in MNRAS

We report the discovery of the hottest hybrid B--type pulsator, KIC\,3240411, that exhibits the period spacing in the low--frequency range. This pattern is associated with asymptotic properties of high-order gravity (g-) modes. Our seismic modelling made simultaneously with the mode identification shows that dipole axisymmetric modes best fit the observations. Evolutionary models are computed with MESA code and pulsational models with the linear non-adiabatic code employing the traditional approximation to include the effects of rotation. The problem of mode excitation is discussed. We confirm that significant modification is indispensable to explain an instability of both pressure and gravity modes in the observed frequency ranges of KIC\,3240411.

--  arXiv:1805.07119v1 [pdf, other] Score: Unrated
A new universal cosmic-ray knee near the magnetic rigidity 10 TV with the NUCLEON space observatory
Comments: 12 pages, 4 figures, 4 pages of Supplemental material (pictures)

Data from the NUCLEON space observatory give a strong indication of the existence of a new universal cosmic ray "knee", which is observed in all groups of nuclei, including heavy nuclei, near a magnetic rigidity of about 10\,TV. Universality means the same position of the knee in the magnetic rigidity scale for all groups of nuclei. The knee is observed by both methods of measurement of particles energy implemented in the NUCLEON observatory---the calorimetric method and the kinematic method KLEM. This new cosmic ray "knee" is probably connected with the limit of acceleration of cosmic rays by some generic or nearby source of cosmic rays.

--  arXiv:1805.07131v1 [pdf, other] Score: Unrated
Time-dependent Pattern Speeds in Barred Galaxies
Comments: 25 pages, 17 figures, 1 table. ApJ accepted

Based on a high quality $N$-body simulation of a double bar galaxy model, we investigate the evolution of the bar properties, including their size, strength and instantaneous pattern speed derived by using three distinct methods: the Fourier, Jacobi integral, and moment of inertia methods. The interaction of the two bars, which rotate at distinct speeds, primarily affects the size, strength and pattern speed of the inner bar. When the two bars are perpendicular to each other, the size and the pattern speed of the inner bar decrease and its strength increases. The emergence of a strong Fourier $m=1$ mode increases the oscillation amplitude of the size, strength and pattern speed of the inner bar. On the other hand, the characteristics of the outer bar are substantially influenced by its adjacent spiral structure. When the spiral structure disappears, the size of the outer bar increases and its strength and pattern speed decrease. Consequently, the ratio of the pattern speed of the outer bar with respect to the inner bar is not constant and increases with time. Overall, the double bar and disk system displays substantial high frequency semi-chaotic fluctuations of the pattern strengths and speeds both in space and time, superposed on the slow secular evolution, which invalidates the assumption that the actions of individual stars should be well conserved in barred galaxies, such as the Milky Way.

--  arXiv:1805.07142v1 [pdf, other] Score: Unrated
Kinetic Sunyaev--Zel'dovich effect in rotating galaxy clusters from MUSIC simulations
Comments: 15 pages; submitted to MNRAS

The masses of galaxy clusters are a key tool to constrain cosmology through the physics of large-scale structure formation and accretion. Mass estimates based on X-ray and Sunyaev--Zel'dovich measurements have been found to be affected by the contribution of non-thermal pressure components, due e.g. to kinetic gas energy. The characterization of possible ordered motions (e.g. rotation) of the intra-cluster medium could be important to recover cluster masses accurately. We update the study of gas rotation in clusters through the maps of the kinetic Sunyaev--Zel'dovich effect, using a large sample of massive synthetic galaxy clusters ($ M_{vir} > 5\times 10^{14} h^{-1}$M$_\odot$ at $z~=~0 $) from MUSIC high-resolution simulations. We select few relaxed objects showing peculiar rotational features, as outlined in a companion work. To verify whether it is possible to reconstruct the expected radial profile of the rotational velocity, we fit the maps to a theoretical model accounting for a specific rotational law, referred as the vp2b model. We find that our procedure allows to recover the parameters describing the gas rotational velocity profile within two standard deviations, both with and without accounting for the bulk velocity of the cluster. The amplitude of the temperature distortion produced by the rotation is consistent with theoretical estimates found in the literature, and it is of the order of 23 per cent of the maximum signal produced by the cluster bulk motion. We also recover the bulk velocity projected on the line of sight consistently with the simulation true value.

--  arXiv:1805.07148v1 [pdf, other] Score: Unrated
A new parametrization of dark energy equation of state leading to double exponential potential
Comments: 10 pages, 13 figures, Accepted for publication in Research in Astronomy and Astrophysics

We show that a canonical scalar field with a phenomenological form of energy density or equivalently an equation of state parameter can provide the required transition from decelerated ($q>0$) to accelerated expansion ($q<0$) phase of the universe. We have used the latest Type Ia Supernova (SNIa) and Hubble parameter datasets to constrain the model parameters. It has been found that for each of these dataset, the transition in deceleration parameter $q$ takes place at the recent past ($z<1$). The future evolution of $q$ is also discussed in the context of the model under consideration. Furthermore, using those datasets, we have reconstructed $\omega_{\phi}(z)$, the equation of state parameter for the scalar field. The results show that the reconstructed forms of $q(z)$ and $\omega_{\phi}(z)$ do not differ much from the standard $\Lambda$CDM value at the current epoch. Finally, the functional form of the relevant potential $V(\phi)$ is derived by a parametric reconstruction from the observational dataset. The corresponding $V(\phi)$ comes out to be a double exponential potential which has a number of cosmological implications. Additionally, we have also studied the effect of this particular scalar field dark energy sector on the evolution of matter over-densities and compared it with the $\Lambda$CDM model.

--  arXiv:1805.07152v1 [pdf, other] Score: Unrated
Bayesian optimisation for likelihood-free cosmological inference
Comments: 15+9 pages, 12 figures

Many cosmological models have only a finite number of parameters of interest, but a very expensive data-generating process and an intractable likelihood function. We address the problem of performing likelihood-free Bayesian inference from such black-box simulation-based models, under the constraint of a very limited simulation budget (typically a few thousand). To do so, we propose an approach based on the likelihood of an alternative parametric model. Conventional approaches to Approximate Bayesian computation such as likelihood-free rejection sampling are impractical for the considered problem, due to the lack of knowledge about how the parameters affect the discrepancy between observed and simulated data. As a response, our strategy combines Gaussian process regression of the discrepancy to build a surrogate surface with Bayesian optimisation to actively acquire training data. We derive and make use of an acquisition function tailored for the purpose of minimising the expected uncertainty in the approximate posterior density. The resulting algorithm (Bayesian optimisation for likelihood-free inference, BOLFI) is applied to the problems of summarising Gaussian signals and inferring cosmological parameters from the Joint Lightcurve Analysis supernovae data. We show that the number of required simulations is reduced by several orders of magnitude, and that the proposed acquisition function produces more accurate posterior approximations, as compared to common strategies.

--  arXiv:1805.07157v1 [pdf, other] Score: Unrated
Hubble Tarantula Treasury Project - VI. Identification of Pre-Main-Sequence Stars using Machine Learning techniques
Comments: 26 pages, 25 figures, Accepted for publication in MNRAS

The Hubble Tarantula Treasury Project (HTTP) has provided an unprecedented photometric coverage of the entire star-burst region of 30 Doradus down to the half Solar mass limit. We use the deep stellar catalogue of HTTP to identify all the pre--main-sequence (PMS) stars of the region, i.e., stars that have not started their lives on the main-sequence yet. The photometric distinction of these stars from the more evolved populations is not a trivial task due to several factors that alter their colour-magnitude diagram positions. The identification of PMS stars requires, thus, sophisticated statistical methods. We employ Machine Learning Classification techniques on the HTTP survey of more than 800,000 sources to identify the PMS stellar content of the observed field. Our methodology consists of 1) carefully selecting the most probable low-mass PMS stellar population of the star-forming cluster NGC 2070, 2) using this sample to train classification algorithms to build a predictive model for PMS stars, and 3) applying this model in order to identify the most probable PMS content across the entire Tarantula Nebula. We employ Decision Tree, Random Forest and Support Vector Machine classifiers to categorise the stars as PMS and Non-PMS. The Random Forest and Support Vector Machine provided the most accurate models, predicting about 20,000 sources with a candidateship probability higher than 50 percent, and almost 10,000 PMS candidates with a probability higher than 95 percent. This is the richest and most accurate photometric catalogue of extragalactic PMS candidates across the extent of a whole star-forming complex.

--  arXiv:1805.07158v1 [pdf, other] Score: Unrated
New classification of solar flares based on the maximum flux in Soft X-rays and on duration of flare
Comments: 25 pages, 9 figures

Solar flare activity is characterized by classification systems, both in optical and Soft X-ray ranges. The most generally accepted classifications of solar flares describe important parameters of flare such as the maximum of brightness of the flare in optical range in $H_{\alpha}$ (flare class in $H_{\alpha}$ is changed from F to B), area of the flare in $H_{\alpha}$ which is changed from S (less than 2 square degrees) to 4 (more than 24.7 square degrees) and the maximum amplitude of the Soft X-ray flux in the band 0.1-0.8 nm (X-ray flare of classes from C to X). A new classification of solar flares which is proposed in this paper -- the X-ray index of flare XI, based on measurements of radiation in the range 0.1-0.8 nm on the GOES satellites. The XI index has a clear physical interpretation associated with the total flare energy in the range 0.1-0.8 nm. XI is easily calculated for each flare with use of available GOES data. The XI index can be used to assess flares along with other important geoeffective parameters.

--  arXiv:1805.07164v1 [pdf, other] Score: Unrated
Planets, candidates, and binaries from the CoRoT/Exoplanet programme: the CoRoT transit catalogue
Comments: Full tables will be provided online at CDS

We provide the catalogue of all transit-like features, including false alarms, detected by the CoRoT exoplanet teams in the 177 454 light curves of the mission. All these detections have been re-analysed with the same softwares so that to ensure their homogeneous analysis. Although the vetting process involves some human evaluation, it also involves a simple binary flag system over basic tests: detection significance, presence of a secondary, difference between odd and even depths, colour dependence, V-shape transit, and duration of the transit. We also gathered the information from the large accompanying ground-based programme carried out on the planet candidates and checked how useful the flag system could have been at the vetting stage of the candidates. In total, we identified and separated 824 false alarms of various kind, 2269 eclipsing binaries among which 616 are contact binaries and 1653 are detached ones, 37 planets and brown dwarfs, and 557 planet candidates. For the planet candidates, the catalogue gives not only their transit parameters but also the products of their light curve modelling, together with a summary of the outcome of follow-up observations when carried out and their current status. Among the planet candidates whose nature remains unresolved, we estimate that 8 +/- 3 planets are still to be identified. We derived planet and brown dwarf occurrences and confirm disagreements with Kepler estimates: small-size planets with orbital period less than ten days are underabundant by a factor of three in the CoRoT fields whereas giant planets are overabundant by a factor of two. These preliminary results would however deserve further investigations using the recently released CoRoT light curves that are corrected of the various instrumental effects and a homogeneous analysis of the stellar populations observed by the two missions.

--  arXiv:1805.07165v1 [pdf, other] Score: Unrated
The universal rotation curve of low surface brightness galaxies IV: the interrelation between dark and luminous matter
Comments: No comment found

We apply the concept of spiral rotation curves universality in order to investigate the properties of the baryonic and dark matter components of low surface brightness galaxies (LSB). The sample is composed by 72 objects, whose rotation curves are selected from literature. After a galaxies' division in five velocity bins according to their increasing optical velocity, we observe that in specifically normalized units the rotation curves are all alike in each selected velocity bin, i.e. it reflects the idea of the universal rotation curve (URC) found in Persic et al. From the mass modeling of our galaxies, we show that the dark matter component is dominant rather than the baryonic one, especially within the smallest and less luminous LSB galaxies. The Burkert profile results to be an optimal model fit for the dark matter halos and it is shown that the central surface density $\Sigma _0 \sim 100 \, M_{\odot} pc^{-2}$, similar to galaxies of different Hubble types and luminosities. Our analysis leads to a strong correlation between the structural properties of the dark and luminous matter. In particular, when we also evaluate the compactness for stars and dark matter, a strong correlation emerges between the stellar disc and dark matter halo. Finally, the introduction of the stellar compactness $C_*$ as a new parameter in the ballpark of the luminous matter besides the optical radius and the optical velocity improves the URC.

--  arXiv:1805.07181v1 [pdf, other] Score: Unrated
Multivariate analysis of cosmic void characteristics
Comments: No comment found

The aim of this study is to distinguish genuine cosmic voids, found in a galaxy catalog by the void finder ZOBOV-VIDE, from underdense regions in a Poisson distribution of objects. For this purpose, we perform two multivariate analyses using the characteristics of voids as input variables. The multivariate analyses are trained on a catalog of voids obtained from a random Poisson distribution of points, used as background, and a catalog of voids identified in a mock catalog of galaxies, used as signal. The classifications are then applied to voids extracted from the Data Release 12 sample of Luminous Red Galaxies in the redshift range 0.45 $\leq$ z $\leq$ 0.7 from the Sloan Digital Sky Survey Baryon Oscillation Spectroscopic Survey (SDSS BOSS DR12 CMASS), showing that the resulting void catalog is nearly free of contamination by Poisson noise.

--  arXiv:1805.07186v1 [pdf, other] Score: Unrated
Dynamical and observational constraints on the Warm Little Inflaton scenario
Comments: 14 pages, 8 figures

We explore the dynamics and observational predictions of the Warm Little Inflaton scenario, presently the simplest realization of warm inflation within a concrete quantum field theory construction. We consider three distinct types of scalar potentials for the inflaton, namely chaotic inflation with a quartic monomial potential, a Higgs-like symmetry breaking potential and a non-renormalizable plateau-like potential. In each case, we determine the parametric regimes in which the dynamical evolution is consistent for 50-60 e-folds of inflation, taking into account thermal corrections to the scalar potential and requiring, in particular, that the two fermions coupled directly to the inflaton remain relativistic and close to thermal equilibrium throughout the slow-roll regime and that the temperature is always below the underlying gauge symmetry breaking scale. We then compute the properties of the primordial spectrum of scalar curvature perturbations and the tensor-to-scalar ratio in the allowed parametric regions and compare them with Planck data, showing that this scenario is theoretically and observationally successful for a broad range of parameter values.

--  arXiv:1805.07188v1 [pdf, other] Score: Unrated
Magnetic Field Saturation of the Ion Weibel Instability in Interpenetrating Relativistic Plasmas
Comments: 4 pages, 4 figures, accepted for publication in ApJL

The time evolution and saturation of the Weibel instability at the ion Alfv\'en current are presented by ab initio particle-in-cell simulations. We found that the ion Weibel current in 3D could evolve into the Alfv\'en current where the magnetic field energy is sustained at 1.5\% of the initial beam kinetic energy. The current filaments are no longer isolated at saturation, but rather connected to each other to form a network structure. Electrons are continuously heated during the coalescence of the filaments, which is crucial for obtaining sustained magnetic fields with much stronger levels than with 2D simulations. The results highlight again the importance of the Weibel instability in generating magnetic fields in laboratory, astrophysical, and cosmological situations.

--  arXiv:1805.07192v1 [pdf, other] Score: Unrated
Spatially Resolved Metal Gas Clouds
Comments: Accepted for publication in MNRAS letters; 5 pages, 3 figures

We now have mounting evidences that the circumgalactic medium (CGM) of galaxies is polluted with metals processed through stars. The fate of these metals is however still an open question and several findings indicate that they remain poorly mixed. A powerful tool to study the low-density gas of the CGM is offered by absorption lines in quasar spectra, although the information retrieved is limited to 1D along the sightline. We report the serendipitous discovery of two close-by bright z_gal=1.148 extended galaxies with a fortuitous intervening z_abs=1.067 foreground absorber. MUSE IFU observations spatially probes kpc-scales in absorption in the plane of the sky over a total area spanning ~30 kpc^-2. We identify two OII emitters at z_abs down to 21 kpc with SFR~2 M_sun/yr. We measure small fractional variations (<30%) in the equivalent widths of FeII and MgII cold gas absorbers on coherence scales of 8kpc but stronger variation on larger scales (25kpc). We compute the corresponding cloud gas mass <2x10^9M_sun. Our results indicate a good efficiency of the metal mixing on kpc-scales in the CGM of a typical z~1 galaxy. This study show-cases new prospects for mapping the distribution and sizes of metal clouds observed in absorption against extended background sources with 3D spectroscopy.

--  arXiv:1805.07212v1 [pdf, other] Score: Unrated
The Discovery of a New Massive Molecular Gas Component Associated with the Submillimeter Galaxy SMM J02399-0136
Comments: 10 pages, 8 figures. Accepted for publication in ApJ 2018.05.11

We present CO(1-0), CO(3-2), and CO(7-6) observations using the Green Bank Telescope (GBT) and the Atacama Large Millimeter Array (ALMA) of the z=2.8 sub-millimeter galaxy SMM J02399-0136. This was the first submillimeter-selected galaxy discovered and remains an archetype of the class, comprising a merger of several massive and active components, including a quasar-luminosity AGN and a highly obscured, gas-rich starburst spread over a ~25 kpc extent. The GBT CO(1-0) line profile is comprised of two distinct velocity components separated by about 600 km/s and suggests the presence of a new component of molecular gas that had not been previously identified. The CO(3-2) observations with ALMA show that this new component, designated W1, is associated with a large extended structure stretching 13 kpc westward from the AGN. W1 is not detected in the ALMA CO(7-6) data implying that this gas has much lower CO excitation than the central starburst regions which are bright in CO(7-6). The molecular gas mass of W1 is about 30% of the total molecular gas mass in the system, depending on the CO--to--H_2 conversion factor. W1 is arguably a merger remnant; alternatively, it could be a massive molecular outflow associated with the AGN, or perhaps inflowing metal-enriched molecular gas fueling the ongoing activity.

--  arXiv:1805.07225v1 [pdf, other] Score: Unrated
The Star Formation History in the M31 Bulge
Comments: The version with all color figures can be downloaded from, 55 pages, 27 figures. The paper has been accepted to be published by the MNRAS

We present the study of stellar populations in the central 5.5' (~1.2 kpc) of the M31 bulge by using the optical color magnitude diagram derived from HST ACS WFC/HRC observations. In order to enhance image quality and then obtain deeper photometry, we construct Nyquist-sampled images and use a deconvolution method to detect sources and measure their photometry. We demonstrate that our method performs better than DOLPHOT in the extremely crowded region. The resolved stars in the M31 bulge have been divided into nine annuli and the color magnitude diagram fitting is performed for each of them. We confirm that the majority of stars (> 70%) in the M31 bulge are indeed very old (>5 Gyr) and metal-rich ([Fe/H] > 0.3). At later times, the star formation rate decreased and then experienced a significant rise around 1 Gyr ago, which pervaded the entire M31 bulge. After that, stars formed at less than 500 Myr ago in the central 130". Through simulation, we find that these intermediate-age stars cannot be the artifacts introduced by the blending effect. Our results suggest that although the majority of the M31 bulge are very old, the secular evolutionary process still continuously builds up the M31 bulge slowly. We compare our star formation history with an older analysis derived from the spectral energy distribution fitting, which suggests that the latter one is still a reasonable tool for the study of stellar populations in remote galaxies.

--  arXiv:1805.07244v1 [pdf, other] Score: Unrated
Global-scale equatorial Rossby waves as an essential component of solar internal dynamics
Comments: This is the submitted version of the paper published in Nature Astronomy. 23 pages, 8 figures, 1 table

The Sun's complex dynamics is controlled by buoyancy and rotation in the convection zone and by magnetic forces in the atmosphere and corona. While small-scale solar convection is well understood, the dynamics of large-scale flows in the solar convection zone is not explained by theory or simulations. Waves of vorticity due to the Coriolis force, known as Rossby waves, are expected to remove energy out of convection at the largest scales. Here we unambiguously detect and characterize retrograde-propagating vorticity waves in the shallow subsurface layers of the Sun at angular wavenumbers below fifteen, with the dispersion relation of textbook sectoral Rossby waves. The waves have lifetimes of several months, well-defined mode frequencies below 200 nHz in a co-rotating frame, and eigenfunctions of vorticity that peak at the equator. Rossby waves have nearly as much vorticity as the convection at the same scales, thus they are an essential component of solar dynamics. We find a transition from turbulence-like to wave-like dynamics around the Rhines scale of angular wavenumber of twenty; this might provide an explanation for the puzzling deficit of kinetic energy at the largest spatial scales.

--  arXiv:1805.07254v1 [pdf, other] Score: Unrated
ELT-scale Adaptive Optics real-time control with thes Intel Xeon Phi Many Integrated Core Architecture
Comments: 10 pages, 12 figures, accepted MNRAS

We propose a solution to the increased computational demands of Extremely Large Telescope (ELT) scale adaptive optics (AO) real-time control with the Intel Xeon Phi Knights Landing (KNL) Many Integrated Core (MIC) Architecture. The computational demands of an AO real-time controller (RTC) scale with the fourth power of telescope diameter and so the next generation ELTs require orders of magnitude more processing power for the RTC pipeline than existing systems. The Xeon Phi contains a large number (> 64) of low power x86 CPU cores and high bandwidth memory integrated into a single socketed server CPU package. The increased parallelism and memory bandwidth are crucial to providing the performance for reconstructing wavefronts with the required precision for ELT scale AO. Here, we demonstrate that the Xeon Phi KNL is capable of performing ELT scale single conjugate AO real-time control computation at over 1.0 kHz with less than 20 {\mu}s RMS jitter. We have also shown that with a wavefront sensor camera attached the KNL can process the real-time control loop at up to 966 Hz, the maximum frame-rate of the camera, with jitter remaining below 20 {\mu}s RMS. Future studies will involve exploring the use of a cluster of Xeon Phis for the real-time control of the MCAO and MOAO regimes of AO. We find that the Xeon Phi is highly suitable for ELT AO real time control.

--  arXiv:1805.07257v1 [pdf, other] Score: Unrated
White dwarfs with a surface electrical charge distribution: Equilibrium and stability
Comments: This is a preprint. The original paper will be published in EPJC

The equilibrium configuration and the radial stability of white dwarfs composed of charged perfect fluid are investigated. These cases are analyzed through the results obtained from the solution of the hydrostatic equilibrium equation. We regard that the fluid pressure and the fluid energy density follow the relation of a fully degenerate electron gas. For the electric charge distribution in the object, we consider that it is centralized only close to the white dwarfs' surfaces. We obtain larger and more massive white dwarfs when the total electric charge is increased. To appreciate the effects of the electric charge in the structure of the star, we found that it must be in the order of $10^{20}\,[{\rm C}]$ with which the electric field is about $10^{16}\,[{\rm V/cm}]$. For white dwarfs with electric fields close to the Schwinger limit, we obtain masses around $2\,M_{\odot}$. We also found that in a system constituted by charged static equilibrium configurations, the maximum mass point found on it marks the onset of the instability. This indicates that the necessary and sufficient conditions to recognize regions constituted by stable and unstable equilibrium configurations against small radial perturbations are respectively $dM/d\rho_c>0$ and $dM/d\rho_c<0$.

--  arXiv:1805.07268v1 [pdf, other] Score: Unrated
Models for Type Ia supernovae and related astrophysical transients
Comments: 20 pages, 2 figures, review published in Space Science Reviews as part of the topical collection on supernovae

We give an overview of recent efforts to model Type Ia supernovae and related astrophysical transients resulting from thermonuclear explosions in white dwarfs. In particular we point out the challenges resulting from the multi-physics multi-scale nature of the problem and discuss possible numerical approaches to meet them in hydrodynamical explosion simulations and radiative transfer modeling. We give examples of how these methods are applied to several explosion scenarios that have been proposed to explain distinct subsets or, in some cases, the majority of the observed events. In case we comment on some of the successes and shortcoming of these scenarios and highlight important outstanding issues.

--  arXiv:1805.07287v1 [pdf, other] Score: Unrated
Multifractality Signatures in Quasars Time Series. I. 3C 273
Comments: 12 pages, 51 figures, 1 table, accepted for publication in MNRAS. arXiv admin note: text overlap with arXiv:1312.3434, arXiv:1506.00586, arXiv:1506.08847 by other authors

The presence of multifractality in a time series shows different correlations for different time scales as well as intermittent behaviour that cannot be captured by a single scaling exponent. The identification of a multifractal nature allows for a characterization of the dynamics and of the intermittency of the fluctuations in non-linear and complex systems. In this study, we search for a possible multifractal structure (multifractality signature) of the flux variability in the quasar 3C 273 time series for all electromagnetic wavebands at different observation points, and the origins for the observed multifractality. This study is intended to highlight how the scaling behaves across the different bands of the selected candidate which can be used as an additional new technique to group quasars based on the fractal signature observed in their time series and determine whether quasars are non-linear physical systems or not. The Multifractal Detrended Moving Average algorithm (MFDMA) has been used to study the scaling in non-linear, complex and dynamic systems. To achieve this goal, we applied the backward ({\theta} = 0) MFDMA method for one-dimensional signals. We observe weak multifractal (close to monofractal) behaviour in some of the time series of our candidate except in the mm, UV and X-ray bands. The non-linear temporal correlation is the main source of the observed multifractality in the time series whereas the heaviness of the distribution contributes less.

--  arXiv:1805.07305v1 [pdf, other] Score: Unrated
Cloud-Cloud Collision Induced Star Formation in IRAS 18223-1243
Comments: 18 pages, 11 figures, 2 tables, Accepted for publication in The Astrophysical Journal

In the direction of l = 17.6 - 19 deg, the star-forming sites Sh 2-53 and IRAS 18223-1243 are prominently observed, and seem to be physically detached from each other. Sh 2-53 has been investigated at the junction of the molecular filaments, while a larger-scale environment of IRAS 18223-1243 remains unexplored. The goal of this paper is to investigate the star formation processes in the IRAS site (area ~0.4 deg x 0.4 deg). Based on the GRS 13CO line data, two molecular clouds, peaking at velocities of 45 and 51 km/s, are found. In the position-velocity plots, a relatively weak 13CO emission is detected at intermediate velocities (i.e. 47.5 - 49.5 km/s) between these two clouds, illustrating a link between two parallel elongated velocity structures. These clouds are physically connected in both space and velocity. The MAGPIS data at 20 cm trace free-free continuum emission toward the IRAS 18223-1243 source. Using the Spitzer and UKIDSS photometric data, we have identified infrared-excess young stellar objects (YSOs), and have observed their groups toward the intersection zones of the clouds. IRAS 18223-1243 is also spatially seen at an interface of the clouds. Considering these observational findings, we propose the onset of the collision of two clouds in the IRAS site about 1 Myr ago, which triggered the birth of massive star(s) and the YSO groups. A non-uniform distribution of the GPIPS H-band starlight mean polarization angles is also observed toward the colliding interfaces, indicating the impact of the collision on the magnetic field morphology.

--  arXiv:1805.07318v1 [pdf, other] Score: Unrated
The fraction of ionizing radiation from massive stars that escapes to the intergalactic medium
Comments: 31 pages

The part played by stars in the ionization of the intergalactic medium remains an open question. A key issue is the proportion of the stellar ionizing radiation that escapes the galaxies in which it is produced. Spectroscopy of gamma-ray burst afterglows can be used to determine the neutral hydrogen column-density in their host galaxies and hence the opacity to extreme ultra-violet radiation along the lines-of-sight to the bursts. Thus, making the reasonable assumption that long-duration GRB locations are representative of the sites of massive stars that dominate EUV production, one can calculate an average escape fraction of ionizing radiation in a way that is independent of galaxy size, luminosity or underlying spectrum. Here we present a sample of NH measures for 138 GRBs in the range 1.6<z<6.7 and use it to establish an average escape fraction at the Lyman limit of <fesc>~0.005, with a 98% confidence upper limit of ~0.015. This analysis suggests that stars provide a small contribution to the ionizing radiation budget of the IGM at z<5, where the bulk of the bursts lie. At higher redshifts, z>5, firm conclusions are limited by the small size of the GRB sample, but any decline in average HI column-density seems to be modest. We also find no indication of a significant correlation of NH with galaxy UV luminosity or host stellar mass, for the subset of events for which these are available. We discuss in some detail a number of selection effects and potential biases. Drawing on a range of evidence we argue that such effects, while not negligible, are unlikely to produce systematic errors of more than a factor ~2, and so would not affect the primary conclusions. Given that many GRB hosts are low metallicity, high specific star-formation rate, dwarf galaxies, these results present a particular problem for the hypothesis that such galaxies dominated the reionization of the universe.

--  arXiv:1805.07328v1 [pdf, other] Score: Unrated
Ground-based optical transmission spectroscopy of the small, rocky exoplanet GJ 1132b
Comments: 18 pages, 9 figures, accepted for publication by AJ

Terrestrial Solar System planets either have high mean molecular weight atmospheres, as with Venus, Mars, and Earth, or no atmosphere at all, as with Mercury. We do not have sufficient observational information to know if this is typical of terrestrial planets or a phenomenon unique to the Solar System. The bulk of atmospheric exoplanet studies have focused on hot Jupiters and Neptunes, but recent discoveries of small, rocky exoplanets transiting small, nearby stars provide targets that are amenable to atmospheric study. GJ 1132b has a radius of 1.2 Earth radii and a mass of 1.6 Earth masses, and orbits an M-dwarf 12 parsecs away from the Solar System. We present results from five transits of GJ 1132b taken with the Magellan Clay Telescope and the LDSS3C multi-object spectrograph. We jointly fit our five data sets when determining the best-fit transit parameters both for the white light curve and wavelength-binned light curves. We bin the light curves into 20 nm wavelength bands to construct the transmission spectrum. Our results disfavor a clear, 10x solar metallicity atmosphere at 3.7 sigma confidence and a 10% H2O, 90% H2 atmosphere at 3.5 sigma confidence. Our data are consistent with a featureless spectrum, implying that GJ 1132b has a high mean molecular weight atmosphere or no atmosphere at all, though we do not account for the possible presence of aerosols. This result is in agreement with theoretical work which suggests that a planet of GJ 1132b's mass and insolation should not be able to retain a H2 envelope.

--  arXiv:1805.07342v1 [pdf, other] Score: Unrated
Gravitino Decay in High Scale Supersymmetry with R-parity Violation
Comments: 27 pages, 4 figures

We consider the effects of R-parity violation due to the inclusion of a bilinear $\mu^\prime L H_u$ superpotential term in high scale supersymmetric models with an EeV scale gravitino as dark matter. Although the typical phenomenological limits on this coupling (e.g. due to lepton number violation and the preservation of the baryon asymmetry) are relaxed when the supersymmetric mass spectrum is assumed to be heavy (in excess of the inflationary scale of $3 \times 10^{13}$ GeV), the requirement that the gravitino be sufficiently long-lived so as to account for the observed dark matter density, leads to a relatively strong bound on $\mu^\prime \lesssim 20$ GeV. The dominant decay channels for the longitudinal component of the gravitino are $Z \nu, W^\pm l^\mp$, and $h\nu$. To avoid an excess neutrino signal in IceCube, our limit on $\mu'$ is then strengthened to $\mu' \lesssim 50$ keV. When the bound is saturated, we find that there is a potentially detectable flux of mono-chromatic neutrinos with EeV energies.

--  arXiv:1805.07347v1 [pdf, other] Score: Unrated
Organic chemistry in a CO2 rich early Earth atmosphere
Comments: No comment found

The emergence of life on the Earth has required a prior organic chemistry leading to the formation of prebiotic molecules. The origin and the evolution of the organic matter on the early Earth is not yet firmly understood. Several hypothesis, possibly complementary, are considered. They can be divided in two categories: endogenous and exogenous sources. In this work we investigate the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the early Earth where the significant VUV contribution of the young Sun involved an efficient formation of reactive species. We address the issue whether this chemistry can lead to the formation of complex organic compounds with CO2 as only source of carbon in an early atmosphere made of N2, CO2 and H2, by mimicking experimentally this type of chemistry using a low pressure plasma reactor. By analyzing the gaseous phase composition, we strictly identified the formation of H2O, NH3, N2O and C2N2. The formation of a solid organic phase is also observed, confirming the possibility to trigger organic chemistry in the upper atmosphere of the early Earth. The identification of Nitrogen-bearing chemical functions in the solid highlights the possibility for an efficient ionospheric chemistry to provide prebiotic material on the early Earth.

--  arXiv:1805.07348v1 [pdf, other] Score: Unrated
Saving Early Disk Formation of Young Stellar Objects from the Magnetic Braking Catastrophe
Comments: 12 pages, submitted to ApJL

Previous observations and ideal magneto-hydrodynamic (MHD) simulations have reported that magnetic fields aligned with the rotation axis, often the bipolar outflow direction, in the youngest protostellar systems prevent a rotationally supported disk from being formed due to efficient magnetic braking, which is known as the magnetic braking catastrophe. We carried out polarimetric observations of the Atacama Large Millimeter/submillimeter Array (ALMA) toward the youngest protostellar system L1448 IRS 2, which is a proto-binary embedded within a flattened, rotating structure, and for which a hint of a central disk has been suggested, but whose magnetic fields are aligned with the bipolar outflow. Our high sensitivity observations show a beautiful hourglass morphology of magnetic fields in the protostellar system, with a toroidal field at the center, which is strong evidence for a circumstellar disk. We have also found a relationship between polarization fractions and intensities, which has various slopes that can be understood through multiple polarization mechanisms, optical depth effects, and depolarization due to field changes. In addition, we found clumpy strips crossing the center perpendicular to the bipolar outflow. Moreover, the magnetic field strength estimated by the Davis-Chandrasekhar-Fermi method is strong enough to hinder formation of a rotationally supported disk, which is inconsistent with the central toroidal field. We conclude that in this source the magnetic braking is not so catastrophic and that non-ideal MHD effects should be considered for a better understanding of early disk and companion star formation in young stellar objects.

--  arXiv:1805.07350v1 [pdf, other] Score: Unrated
A Gaia DR~2 and VLT/FLAMES search for new satellites of the LMC
Comments: 12 pages, 9 figures, 3 tables, submitted to A&A, comments welcome

A wealth of tiny galactic systems populates the surroundings of the Milky Way. However, some of these objects might actually have their origin as former satellites of the Magellanic Clouds, in particular the LMC. An example of the importance of understanding how many systems are genuine satellites of the Milky Way or the LMC are the implications that the number and luminosity/mass function of satellites around hosts of different mass have for dark matter theories and treatment of baryonic physics in simulations of structure formation. Here we aim at deriving the bulk motions and estimates of the internal velocity dispersion and metallicity properties in four recently discovered southern dwarf galaxies, Columba~I, Reticulum~III, Phoenix~II and Horologium~II. We combine Gaia DR2 astrometric measurements and photometry to new FLAMES/GIRAFFE intermediate resolution spectroscopic data in the region of the nearIR Ca~II triplet lines; such combination is essential for finding potential member stars in these low luminosity systems. We find very likely member stars in all four satellites and are able to determine (or place limits on) the systems bulk motions and average internal properties. The systems are found to be very metal-poor, in agreement with dwarf galaxies and dwarf galaxy candidates of similar luminosity. Among the four systems, the only one that we can place in the category of dwarf galaxies is Phoenix~II given its resolved large velocity dispersion ($7.1_{-1.1}^{+1.5}\,$ km/s) and intrinsic metallicity spread (0.34$\,$dex). The orbital pole of Phoenix~II is well constrained and close to the orbital pole of the LMC, suggesting a prior association. The uncertainty on the orbital poles of the other systems are presently very large, and in the case of Horologium~II dependent on the sample of members adopted, making an association not impossible.

--  arXiv:1805.07352v1 [pdf, other] Score: Unrated
Quantitative Spectroscopy of Supergiants in the Local Group Dwarf Galaxy IC 1613: Metallicity and Distance
Comments: 12 pages, 9 figures, 1 table. Accepted for publication in ApJ. For a brief video explaining this paper, see

We present the spectral analysis of 21 blue supergiant stars of spectral type late B to early A within the Local Group dwarf galaxy IC 1613 based on VLT-FORS2 low resolution spectra. Combining our results with studies of early B type blue supergiants we report a wide bi-modal distribution of metallicities with two peaks around [Z] $\sim -0.50$ dex and [Z] $\sim -0.85$ dex. The bi-modal distribution correlates with spatial location, when compared with column densities of neutral hydrogen in IC 1613. While the low [Z] objects appear in regions of relatively high ISM HI column densities or close to them, the high [Z] supergiants are found in the central HI hole almost devoid of hydrogen. This suggests varied chemical evolution histories of the young stellar populations in IC 1613. Utilizing the Flux-Weighted Gravity-Luminosity Relation (FGLR), we determine IC 1613's distance modulus as $m - M$ = 24.39 $\pm$ 0.11 mag. This value is in agreement within previous distance measurements using the near-infrared period-luminosity relationship of Cepheids and the tip of the red giant branch.