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J.P. Magué & B. Ménard

[1]
Title: Star Formation Histories of the LEGUS dwarf galaxies. II. Spatially resolved star formation history of the Magellanic irregular NGC 4449
Comments: 16 pages, 25 figures. Accepted for publication in the Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a detailed study of the Magellanic irregular galaxy NGC 4449 based on both archival and new photometric data from the Legacy Extragalactic UV Survey, obtained with the Hubble Space Telescope Advanced Camera for Surveys and Wide Field Camera 3. Thanks to its proximity ($D=3.82\pm 0.27$ Mpc) we reach stars 3 magnitudes fainter than the tip of the red giant branch in the F814W filter. The recovered star formation history spans the whole Hubble time, but due to the age-metallicity degeneracy of the red giant branch stars, it is robust only over the lookback time reached by our photometry, i.e. $\sim 3$ Gyr. The most recent peak of star formation is around 10 Myr ago. The average surface density star formation rate over the whole galaxy lifetime is $0.01$ M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$. From our study it emerges that NGC 4449 has experienced a fairly continuous star formation regime in the last 1 Gyr with peaks and dips whose star formation rates differ only by a factor of a few. The very complex and disturbed morphology of NGC 4449 makes it an interesting galaxy for studies of the relationship between interactions and starbursts, and our detailed and spatially resolved analysis of its star formation history does indeed provide some hints on the connection between these two phenomena in this peculiar dwarf galaxy.

[2]
Title: Very Massive Stars: a metallicity-dependent upper-mass limit, slow winds, and the self-enrichment of Globular Clusters
Authors: Jorick S. Vink (Armagh Observatory and Planetarium)
Comments: 9 pages, 3 figures. Accepted by Astronomy & Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

One of the key questions in Astrophysics concerns the issue of whether there exists an upper-mass limit to stars, and if so, what physical mechanism sets this limit, which might also determine if the upper-mass limit is metallicity (Z) dependent. We argue that mass loss by radiation-driven winds mediated by line opacity is one of the prime candidates setting the upper-mass limit. We present mass-loss predictions (dM/dt_wind) from Monte Carlo radiative transfer models for relatively cool (Teff = 15kK) inflated very massive stars (VMS) with large Eddington Gamma factors in the mass range 100-1000 Msun as a function of metallicity down to 1/100 Z/Zsun. We employ a hydrodynamic version of our Monte Carlo method, allowing us to predict the rate of mass loss (dM/dt_wind) and the terminal wind velocity (vinf) simultaneously. Interestingly, we find wind terminal velocities (vinf) that are low (100-500 km/s) over a wide Z-range, and we propose that the slow winds from VMS are an important source of self-enrichment in globular clusters. We also find mass-loss rates (dM/dt_wind), exceeding the typical mass-accretion rate (dM/dt_accr) of 0.001 Msun/yr during massive-star formation. We express our mass-loss predictions as a function of mass and Z, finding log dM/dt = -9.13 + 2.1 log(M/Msun) + 0.74 log(Z/Zsun) (Msun/yr). Even if stellar winds would not directly halt & reverse mass accretion during star formation, if the most massive stars form by stellar mergers stellar wind mass loss may dominate over the rate at which stellar growth takes place. We therefore argue that the upper-mass limit is effectively Z-dependent due to the nature of radiation-driven winds. This has dramatic consequences for the most luminous supernovae, gamma-ray bursts, and other black hole formation scenarios at different Cosmic epochs.

[3]
Title: Spectropolarimetry of Galactic stars with anomalous extinction sightlines
Comments: accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Highly reddened type Ia Supernovae (SNe Ia) with low total-to-selective visual extinction ratio values, $R_V$, also show peculiar linear polarization wavelength dependencies with peak polarizations at short wavelengths ($\lambda_{max} \lesssim 0.4 \mu m$). It is not clear why sightlines to SNe Ia display such different continuum polarization profiles from interstellar sightlines in the Milky Way with similar $R_V$ values. We investigate polarization profiles of a sample of Galactic stars with low $R_V$ values, along anomalous extinction sightlines, with the aim to find similarities to the polarization profiles that we observe in SN Ia sightlines. We undertook spectropolarimetry of 14 stars, and used archival data for three additional stars, and run dust extinction and polarization simulations to infer a simple dust model that can reproduce the observed extinction and polarization curves. Our sample of Galactic stars with low $R_V$ values and anomalous extinction sightlines displays normal polarization profiles with an average $\lambda_{max} \sim 0.53 {\mu m}$, and is consistent within 3$\sigma$ to a larger coherent sample of Galactic stars from literature. Despite the low $R_V$ values of dust towards the stars in our sample, the polarization curves do not show any similarity to the continuum polarization curves observed towards SNe Ia with low $R_V$ values. There is a correlation between the best-fit Serkowski parameters $K$ and $\lambda_{max}$, but we did not find any significant correlation between $R_V$ and $\lambda_{max}$. Our simulations show that the $K-\lambda_{max}$ relationship is an intrinsic property of polarization. Furthermore, we have shown that in order to reproduce polarization curves with normal $\lambda_{max}$ and low $R_V$ values, a population of large (a $\geq 0.1 \mu m$) interstellar silicate grains must be contained in the dust's composition.

[4]
Title: Star-forming galaxies at low-redshift in the SHARDS survey
Comments: Accepted for publication in Astronomy & Astrophysics. 17 pages, 17 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The physical processes driving the evolution of star formation (SF) in galaxies over cosmic time still present many open questions. Recent galaxy surveys allow now to study these processes in great detail at intermediate redshift. In this work, we build a complete sample of star-forming galaxies and analyze their properties, reaching systems with low stellar masses and low star formation rates (SFRs) at intermediate-to-low redshift. We use data from the SHARDS multiband survey in the GOODS-North field. Its depth (up to magnitude $\langle m_{3\sigma}\rangle\sim26.5$) and its spectro-photometric resolution ($R\sim50$) provides us with an ideal dataset to search for emission line galaxies (ELGs). We develop a new algorithm to identify low-redshift ($z$<0.36) ELGs by detecting the [OIII]5007 and $H\alpha$ emission lines simultaneously. We fit the spectral energy distribution (SED) of the selected sample, using a model with two single stellar populations. We find 160 star-forming galaxies with equivalent widths (EWs) as low as 12 {\AA}, with median values for the sample of $\sim$ 35 {\AA} in [OIII]5007 and $\sim$ 56 {\AA} in $H\alpha$, respectively. Results from the SED fitting show a young stellar population with low median metallicity (36% of the solar value) and extinction ($A_V \sim$ 0.37), with median galaxy stellar mass $\sim$ 10$^{8.5}$ M$_{\odot}$. Gas-phase metallicities measured from available spectra are also low. ELGs in our sample present bluer colors in the UVJ plane than the median color-selected star-forming galaxy in SHARDS. We suggest a new (V-J) color criterion to separate ELGs from non-ELGs in blue galaxy samples. In addition, several galaxies present high densities of O-type stars. Robust fits to the full SEDs can only be obtained including an old stellar population, suggesting the young component is built up by a recent burst of SF in an otherwise old galaxy.

[5]
Title: Millisecond Pulsars, TeV Halos, and Implications For The Galactic Center Gamma-Ray Excess
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

Observations by HAWC indicate that many young pulsars (including Geminga and Monogem) are surrounded by spatially extended, multi-TeV emitting regions. It is not currently known, however, whether TeV emission is also produced by recycled, millisecond pulsars (MSPs). In this study, we perform a stacked analysis of 24 MSPs within HAWC's field-of-view, finding between 2.6-3.2 sigma evidence that these sources are, in fact, surrounded by TeV halos. The efficiency with which these MSPs produce TeV halos is similar to that exhibited by young pulsars. This result suggests that several dozen MSPs will ultimately be detectable by HAWC, including many "invisible" pulsars without radio beams oriented in our direction. The TeV halos of unresolved MSPs could also dominate the TeV-scale diffuse emission observed at high galactic latitudes. We also discuss the possibility that TeV and radio observations could be used to constrain the population of MSPs that is present in the inner Milky Way, thereby providing us with a new way to test the hypothesis that MSPs are responsible for the Galactic Center GeV excess.

[6]
Title: Gravitational waves from asymmetric oscillon dynamics?
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

It has been recently suggested that oscillons produced in the early universe from certain asymmetric potentials continue to emit gravitational waves for a number of $e$-folds of expansion after their formation, leading to potentially detectable gravitational wave signals. We revisit this claim by conducting a convergence study using GPU-accelerated lattice simulations and show that numerical errors accumulated with time are significant in low-resolution scenarios, or in scenarios where the run-time causes the resolution to drop below the relevant scales in the problem. Our study suggests that the dominant, growing high frequency peak of the gravitational wave signals in the fiducial "hill-top model" [arXiv:1607.01314] is a numerical artifact.

[7]
Title: Hidden in plain sight: a massive, dusty starburst in a galaxy protocluster at z=5.7 in the COSMOS field
Comments: 15 pages, 7 figures, 4 tables, submitted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We report the serendipitous discovery of a dusty, starbursting galaxy at z=5.667 (called CRLE hereafter), in close physical association to the "normal" Main Sequence galaxy HZ10 at z=5.654. CRLE was identified by detection of [CII], [NII] and CO(2-1) line emission, making it the highest redshift, most luminous starburst in the COSMOS field. This massive, dusty galaxy appears to be forming stars at a rate of at least 1500$\,M_\odot$ yr$^{-1}$ in a compact region only ~3 kpc in diameter. The dynamical and dust emission properties of CRLE suggest an ongoing merger driving the starburst, in a potentially intermediate stage relative to other known dusty galaxies at the same epoch. The ratio of [CII] to [NII] may suggest that an important contribution to the [CII] emission comes from a diffuse ionized gas component, which could be more extended than the dense, starbursting gas. CRLE appears to be located in a significant galaxy overdensity at the same redshift, potentially associated with a large scale cosmic structure recently identified in a Lyman Alpha Emitter survey. This overdensity suggests that CRLE and HZ10 reside in a protocluster environment, offering the tantalizing opportunity to study the effect of a massive starburst on protocluster star formation. Our findings support the interpretation that a significant fraction of the earliest galaxy formation may occur from the inside-out, within the central regions of the most massive halos, while rapidly evolving into the massive galaxy clusters observed in the local Universe.

[8]
Title: BCG Mass Evolution in Cosmological Hydro-Simulations
Comments: 11 pages, 9 figures, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We analyze the stellar growth of Brightest Cluster Galaxies (BCGs) produced by cosmological zoom-in hydrodynamical simulations of the formation of massive galaxy clusters. The evolution of the stellar mass content is studied considering different apertures, and tracking backwards either the main progenitor of the $z=0$ BCG or that of the cluster hosting the BCG at $z=0$. Both methods lead to similar results up to $z \simeq 1.5$. The simulated BCGs masses at $z=0$ are in agreement with recent observations. In the redshift interval from z=1 to z=0 we find growth factors 1.3, 1.6 and 3.6 for stellar masses within 30kpc, 50kpc and 10% of R_{500} respectively. The first two factors, and in general the mass evolution in this redshift range, are in agreement with most recent observations. The last larger factor is similar to the growth factor obtained by a semi-analytical model (SAM). Half of the star particles that end up in the inner 50 kpc was typically formed by redshift about 3.7, while the assembly of half of the BCGs stellar mass occurs on average at lower redshifts $\sim 1.5$. This assembly redshift correlates with the mass attained by the cluster at high $z \gtrsim 1.3$, due to the broader range of the progenitor clusters at high-z. The assembly redshift of BCGs decreases with increasing apertures. Our results are compatible with the inside-out scenario. Simulated BCGs could lack intense enough star formation (SF) at high redshift, while possibly exhibit an excess of residual SF at low redshift.

[9]
Title: Sub-photospheric fluctuations in magnetized radiative envelopes: contribution from unstable magnetosonic waves
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

We examine the excitation of unstable magnetosonic waves in the radiative envelopes of intermediate- and high-mass stars with a magnetic field of ~kG strength. Wind clumping close to the star and microturbulence can often be accounted for when including small-scale, sub-photospheric density or velocity perturbations. Compressional waves - with wavelengths comparable to or shorter than the gas pressure scale height - can be destabilized by the radiative flux in optically-thick media when a magnetic field is present, in a process called the Radiation-Driven Magneto-Acoustic Instability (RMI). The instability does not require radiation or magnetic pressure to dominate over gas pressure, and acts independently of sub-surface convection zones. Here we evaluate the conditions for the RMI to operate on a grid of stellar models covering a mass range $3-40M_\odot$ at solar metallicity. For a uniform 1kG magnetic field, fast magnetosonic modes are unstable down to an optical depth of a few tens, while unstable slow modes extend beyond the depth of the iron convection zone. The qualitative behavior is robust to magnetic field strength variations by a factor of a few. When combining our findings with previous results for the saturation amplitude of the RMI, we predict velocity fluctuations in the range ~0.1-10 km/s. These amplitudes are a monotonically increasing function of the ratio of radiation to gas pressure, or alternatively, of the zero-age main sequence mass.

[10]
Title: A quartet of black holes and a missing duo: probing the low-end of the Mbh - sigma relation with the adaptive optics assisted integral-field spectroscopy
Comments: 36 pages, 23 figures (slightly degraded, full resolution can be found see this https URL ); accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present mass estimates of supermassive black holes in six nearby fast rotating early-type galaxies (NGC4339, NGC4434, NGC4474, NGC4551, NGC4578 and NGC4762) with effective stellar velocity dispersion around 100 km/s. We use near-infrared laser-guide adaptive optics observations with the GEMINI/NIFS to derive stellar kinematics in the galactic nuclei, and SAURON observations from the ATLAS3D Survey for large-scale kinematics. We build axisymmetric Jeans Anisotropic Models and axisymmetric Schwarzschild dynamical models. Both modelling approaches recover consistent orbital anisotropies and black hole masses within 1-2sigma confidence level, except for one galaxy for which the difference is just above the 3sigma level. Two black holes (NGC4339 and NGC4434) are amongst the largest outliers from the current black hole mass - velocity dispersion relation, with masses of $(4.3^{+4.8}_{-2.3})\times10^7$ and $(7.0^{+2.0}_{-2.8})\times10^7$ M$_\odot$, respectively ($3\sigma$ confidence level). The black holes in NGC4578 and NGC4762 lie on the scaling relation with masses of $(1.9^{+0.6}_{-1.4})\times10^7$ and $(2.3^{+0.9}_{-0.6})\times10^7$ M$_\odot$, respectively (3sigma confidence level). For two galaxies (NGC4474 and NGC4551) we are able to place upper limits on their black holes masses ($<7\times10^6$ and $<5\times10^6$ M$_\odot$, respectively, $3\sigma$ confidence level). The kinematics for these galaxies clearly indicate central velocity dispersion drops within a radius of 35 pc and 80 pc, respectively. These drops cannot be associated with cold stellar structures and our data do not have the resolution to exclude black holes with masses an order of magnitude smaller than the predictions. Parametrising the orbital distribution in spherical coordinates, the vicinity of the black holes is characterised by isotropic or mildly tangential anisotropy.

[11]
Title: Structural and Dynamical Properties of Galaxies in a Hierarchical Universe: Sizes and Specific Angular Momenta
Comments: 26 pages, 14 figures, 2 appendices. Submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We study the size and the specific angular momentum of galaxies in a state-of-the-art semi-analytic model. Our model includes a specific treatment for the exchange of angular momentum between different galactic components. Disk scale radii are estimated from the angular momentum of the gaseous/stellar disk, while bulge sizes are estimated using energy conservation arguments. The predicted size-mass and angular momentum-mass relations are in good agreement with observational measurements in the local Universe, provided a treatment for gas dissipation during major mergers is included. Our treatment for disk instability leads to unrealistically small radii of bulges formed predominantly through disk instability, and predicts an offset between the size-mass relations predicted for central and satellite early-type galaxies, that is not observed in real samples. The model reproduces well the observed dependence on morphology, and predicts a strong correlation between the specific angular momentum of galaxies and their cold gas content. We find that this correlation is a natural consequence of galaxy evolution: gas-rich galaxies form in smaller halos, and form stars gradually until present day, while gas-poor ones reside in large halos, and form most of their stars at early epochs, when the angular momentum of their parent halos is low. The dynamical and structural properties of galaxies in the local Universe can be strongly affected by a different treatment for stellar feedback, as this would modify the star formation history of model galaxies. A higher angular momentum for gas accreted through rapid mode does not affect significantly the properties of massive galaxies today, but has a more important effect on low-mass galaxies and at higher redshift.

[12]
Title: Resolution Convergence in Cosmological Hydrodynamical Simulations Using Adaptive Mesh Refinement
Comments: 23 pages, 22 figures, 1 table, accepted for publication in MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We have explored the evolution of gas distributions from cosmological simulations carried out using the RAMSES adaptive mesh refinement (AMR) code, to explore the effects of resolution on cosmological hydrodynamical simulations. It is vital to understand the effect of both the resolution of initial conditions and the final resolution of the simulation. Lower initial resolution simulations tend to produce smaller numbers of low mass structures. This will strongly affect the assembly history of objects, and has the same effect of simulating different cosmologies. The resolution of initial conditions is an important factor in simulations, even with a fixed maximum spatial resolution. The power spectrum of gas in simulations using AMR diverges strongly from the fixed grid approach - with more power on small scales in the AMR simulations - even at fixed physical resolution and also produces offsets in the star formation at specific epochs. This is because before certain times the upper grid levels are held back to maintain approximately fixed physical resolution, and to mimic the natural evolution of dark matter only simulations. Although the impact of hold back falls with increasing spatial and initial-condition resolutions, the offsets in the star formation remain down to a spatial resolution of 1 kpc. These offsets are of order of 10-20%, which is below the uncertainty in the implemented physics but are expected to affect the detailed properties of galaxies. We have implemented a new grid-hold-back approach to minimize the impact of hold back on the star formation rate.

[13]
Title: Gaian bottlenecks and planetary habitability maintained by evolving model biospheres: The ExoGaia model
Comments: Accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The search for habitable exoplanets inspires the question - how do habitable planets form? Planet habitability models traditionally focus on abiotic processes and neglect a biotic response to changing conditions on an inhabited planet. The Gaia hypothesis postulates that life influences the Earth's feedback mechanisms to form a self-regulating system, and hence that life can maintain habitable conditions on its host planet. If life has a strong influence, it will have a role in determining a planet's habitability over time. We present the ExoGaia model - a model of simple 'planets' host to evolving microbial biospheres. Microbes interact with their host planet via consumption and excretion of atmospheric chemicals. Model planets orbit a 'star' which provides incoming radiation, and atmospheric chemicals have either an albedo, or a heat-trapping property. Planetary temperatures can therefore be altered by microbes via their metabolisms. We seed multiple model planets with life while their atmospheres are still forming and find that the microbial biospheres are, under suitable conditions, generally able to prevent the host planets from reaching inhospitable temperatures, as would happen on a lifeless planet. We find that the underlying geochemistry plays a strong role in determining long-term habitability prospects of a planet. We find five distinct classes of model planets, including clear examples of 'Gaian bottlenecks' - a phenomenon whereby life either rapidly goes extinct leaving an inhospitable planet, or survives indefinitely maintaining planetary habitability. These results suggest that life might play a crucial role in determining the long-term habitability of planets.

[14]
Title: Sunstardb: a database for the study of stellar magnetism and the solar-stellar connection
Authors: Ricky Egeland
Comments: 10 pages, 2 figures, 1 table. Accepted for publication in ApJS special issue "Data: Insights and Challenges in a Time of Abundance." Project URL: this https URL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Instrumentation and Methods for Astrophysics (astro-ph.IM)

The "solar-stellar connection" began as a relatively small field of research focused on understanding the processes that generate magnetic field in stars and which sometimes lead to a cyclic pattern of long-term variability in activity, as demonstrated by our Sun. This area of study has recently become more broadly pertinent to questions of exoplanet habitability and exo-space weather, as well as stellar evolution. In contrast to other areas of stellar research, individual stars in the solar-stellar connection often have a distinct identity and character in the literature, due primarily to the rarity of the decades-long time series that are necessary for studying stellar activity cycles. Furthermore, the underlying stellar dynamo is not well understood theoretically, and is thought to be sensitive to several stellar properties, e.g. luminosity, differential rotation, and depth of the convection zone, which in turn are often parameterized by other more readily available properties. Relevant observations are scattered throughout the literature and existing stellar databases, and consolidating information for new studies is a tedious and laborious exercise. To accelerate research in this area I developed sunstardb, a relational database of stellar properties and magnetic activity proxy time series keyed by individual named stars. The organization of the data eliminates the need for problematic catalog cross matching operations inherent when building an analysis dataset from heterogeneous sources. In this article I describe the principles behind sunstardb, the data structures and programming interfaces, as well as use cases from solar-stellar connection research.

[15]
Title: Chandra X-rays from the redshift 7.54 quasar ULAS J1342+0928
Comments: Accepted for publication in the Astrophysical Journal Letters
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a 45 ks Chandra observation of the quasar ULAS J1342+0928 at z=7.54. We detect 14.0^{+4.8}_{-3.7} counts from the quasar in the observed-frame energy range 0.5-7.0 keV (6-sigma detection), representing the most distant non-transient astronomical source identified in X-rays to date. The present data are sufficient only to infer rough constraints on the spectral parameters. We find an X-ray hardness ratio of HR = -0.51^{+0.26}_{-0.28} between the 0.5-2.0 keV and 2.0-7.0 keV ranges and derive a power-law photon index of Gamma = 1.95^{+0.55}_{-0.53}. Assuming a typical value for high-redshift quasars of Gamma = 1.9, ULAS J1342+0928 has a 2-10 keV rest-frame X-ray luminosity of L_{2-10} = 11.6^{+4.3}_{-3.5} x 10^{44} erg/s. Its X-ray-to-optical power-law slope is alpha_{OX}=-1.67^{+0.16}_{-0.10}, consistent with the general trend indicating that the X-ray emission in the most bolometrically powerful quasars is weaker relative to their optical emission.

[16]
Title: Constraints for the Progenitor Masses of Historic Core-Collapse Supernovae
Comments: 12 pages, 4 tables, 4 figures, accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We age-date the stellar populations associated with 12 historic nearby core-collapse supernovae (CCSNe) and 2 supernova impostors, and from these ages, we infer their initial masses and associated uncertainties. To do this, we have obtained new HST imaging covering these CCSNe. Using these images, we measure resolved stellar photometry for the stars surrounding the locations of the SNe. We then fit the color-magnitude distributions of this photometry with stellar evolution models to determine the ages of any young existing populations present. From these age distributions, we infer the most likely progenitor mass for all of the SNe in our sample. We find ages between 4 and 50 Myr, corresponding to masses from 7.5 to 59 solar masses. There were no SNe that lacked a young population within 50~pc. Our sample contains 4 type Ib/c SNe; their masses have a wide range of values, suggesting that the progenitors of stripped-envelope SNe are binary systems. Both impostors have masses constrained to be $\lesssim$7.5 solar masses. In cases with precursor imaging measurements, we find that age-dating and precursor imaging give consistent progenitor masses. This consistency implies that, although the uncertainties for each technique are significantly different, the results of both are reliable to the measured uncertainties. We combine these new measurements with those from our previous work and find that the distribution of 25 core-collapse SNe progenitor masses is consistent with a standard Salpeter power-law mass function, no upper mass cutoff, and an assumed minimum mass for core-collapse of 7.5~M$_{\odot}$.

[17]
Title: Constraints on mass, spin and magnetic field of microquasar H~1743-322 from observations of QPOs
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The study of quasi-periodic oscillations (QPOs) of X-ray flux observed in many microquasars can provide a powerful tool for testing of the phenomena occurring in strong gravity regime. QPOs phenomena can be well related to the oscillations of charged particles in accretion disks orbiting Kerr black holes immersed in external large-scale magnetic fields. In the present paper we study the model of magnetic relativistic precession and provide estimations of the mass and spin of the central object of the microquasar H~1743-322 which is a candidate for a black hole. Moreover, we discuss the possible values of external magnetic field and study its influence on the motion of charged particles around rotating black hole.

[18]
Title: Detection of the closest Jovian exoplanet in the Epsilon Indi triple system
Comments: 9 pages, 6 figures, submitted to MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We confirm the trend in the radial velocity data for Epsilon Indi A suggesting a long-period planetary companion and find significant curvature is present, sufficient to quantify Epsilon Indi Ab as a cold Jupiter with a minimum mass of $2.71_{-0.44}^{+2.19}~M_{\rm Jup}$ on a nearly circular orbit with a semi-major axis of $12.82_{-0.71}^{+4.18}$ au and an orbital period of $52.62_{-4.12}^{+27.70}$ yr. We also identify other significant signals in the radial velocity data. We investigate a variety of spectral diagnostics and interpret these signals as arising from activity-induced radial velocity variations. In particular, the 2500 and 278 d signals are caused by magnetic cycles. While a planetary signal might be present in the 17.8 d signal, the origin of 17.8 and 11 d signals are most easily interpreted as arising in the rotation of the star with a period of about 35 d. We find that traditional activity indicators have a variety of sensitivities. In particular, the sodium lines and CaHK index are sensitive to all activity-induced signals. The line bisector measurement is sensitive to stellar rotation signal while H$\alpha$ is sensitive to the secondary magnetic cycle. In general, because of their different sensitivities these activity indicators introduce extra noise if included in the noise model whereas differential RVs provide a robust proxy to remove wavelength-dependent noise efficiently. Based on these analyses, we propose an activity diagnostics procedure for the detection of low amplitude signals in high precision radial velocity data. Thus the Epsilon Indi system comprises of at least Epsilon Indi A, Ab as well as a long period brown dwarf binary Ba and Bb; so it provides a benchmark case for our understanding of the formation of gas giants and brown dwarfs.

[19]
Title: Clear and Cloudy Exoplanet Forecasts for JWST: Maps, Retrieved Composition and Constraints on Formation with MIRI and NIRCam
Comments: Submitted to AAS Journals, 17 pages
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The James Webb Space Telescope (JWST) will measure exoplanet transmission and eclipse spectroscopy at un-precedented precisions to better understand planet structure, dynamics, chemistry and formation. These are essential tools on the march towards biosignatures searches on potentially habitable planets. We explore a range of exoplanet atmospheric conditions and forecast the expected results with JWST. We take realistic CHIMERA models that match existing Spitzer and HST results and simulate the spectra achievable with the JWST MIRI + NIRCam Guaranteed Time Observations (GTO) survey. We then retrieve atmospheric parameters from these spectra to estimate the precision to which the planets' atmospheric compositions can be measured. We find that emission spectra have well-constrained unimodal solutions but transmission spectra near 10X solar abundance and solar C/O ratios can suffer from bimodal solutions. Broad wavelength coverage as well as higher precision data can resolve bimodal solutions and provide dramatically better atmospheric parameter constraints. We find that metallicities can be measured to within 20% to 170%, which approaches the precisions on Solar System planets, and C/O ratios can be constrained to ~10% to 60%, assuming that observers can leverage short wavelength data to select the correct solution from the bimodal posteriors. These compositional precisions are sufficient to validate or refute predictions from disk formation models on final atmospheric abundances as long as their history is not erased by planet evolution processes. We also show the extent to which eclipse mapping with JWST is possible on our brightest system HD 189733 b.

[20]
Title: Development of a Mach-Zehnder Modulator Photonic Local Oscillator Source
Comments: IEEE Transactions on Microwave Theory and Techniques, July 2013
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

This paper describes the development of a photonic local oscillator (LO) source based on a 3-stage Mach-Zehnder modulator (MZM) device. The MZM laser synthesizer demonstrates the feasibility of providing the photonic reference LO for the Atacama Large Millimeter Array telescope located in Chile. This MZM approach to generating an LO by radio RF modulation of a monochromatic optical source provides the merits of wide frequency coverage of 4-130 GHz, tuning speed of about 0.2 seconds, and residual integrated phase noise performance of 0.3 degrees RMS at 100 GHz.

[21]
Title: Limits on turbulent propagation of energy in cool-core clusters of galaxies
Comments: 5 pages, 3 figures, Accepted for publication in MNRAS Letters
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA)

We place constraints on the propagation velocity of bulk turbulence within the intracluster medium of three clusters and an elliptical galaxy. Using Reflection Grating Spectrometer measurements of turbulent line broadening, we show that for these clusters, the 90% upper limit on turbulent velocities when accounting for instrumental broadening is too low to propagate energy radially to the cooling radius of the clusters within the required cooling time. In this way, we extend previous Hitomi-based analysis on the Perseus cluster to more clusters, with the intention of applying these results to a future, more extensive catalog. These results constrain models of turbulent heating in AGN feedback by requiring a mechanism which can not only provide sufficient energy to offset radiative cooling, but resupply that energy rapidly enough to balance cooling at each cluster radius.

[22]
Title: The Zeldovich approximation and wide-angle redshift-space distortions
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The contribution of line-of-sight peculiar velocities to the observed redshift of objects breaks the translational symmetry of the underlying theory, modifying the predicted 2-point functions. These wide angle effects' have mostly been studied using linear perturbation theory in the context of the multipoles of the correlation function and power spectrum. In this work we present the first calculation of wide angle terms in the Zeldovich approximation, which is known to be more accurate than linear theory on scales probed by the next generation of galaxy surveys. We present the exact result for dark matter and perturbatively biased tracers as well as the small angle expansion of the configuration- and Fourier-space two-point functions and the connection to the multi-frequency angular power spectrum. We compare different definitions of the line-of-sight direction and discuss how to translate between them. We show that wide angle terms can reach tens of percent of the total signal in a measurement at low redshift in some approximations, and that a generic feature of wide angle effects is to slightly shift the Baryon Acoustic Oscillation scale.

[23]
Title: Distortion of Magnetic Fields in a Starless Core III: Polarization--Extinction Relationship in FeSt 1-457
Comments: Accepted to the Astrophysical Journal (ApJ)
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The relationship between dust polarization and extinction was determined for the cold dense starless molecular cloud core FeSt 1-457 based on the background star polarimetry of dichroic extinction at near-infrared wavelengths. Owing to the known (three-dimensional) magnetic field structure, the observed polarizations from the core were corrected by considering (a) the subtraction of the ambient polarization component, (b) the depolarization effect of inclined distorted magnetic fields, and (c) the magnetic inclination angle of the core. After these corrections, a linear relationship between polarization and extinction was obtained for the core in the range up to $A_V \approx 20$ mag. The initial polarization vs. extinction diagram changed dramatically after the corrections of (a) to (c), with the correlation coefficient being refined from 0.71 to 0.79. These corrections should affect the theoretical interpretation of the observational data. The slope of the finally obtained polarization--extinction relationship is $P_H / E_{H-K_s} = 11.00 \pm 0.72$ $\%$ ${\rm mag}^{-1}$, which is close to the statistically estimated upper limit of the interstellar polarization efficiency (Jones 1989). This consistency suggests that the upper limit of interstellar polarization efficiency might be determined by the observational viewing angle toward polarized astronomical objects.

[24]
Title: Low-Frequency Carbon Recombination Lines in the Orion Molecular Cloud Complex
Comments: This paper is accepted for publication in PASA
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We detail tentative detections of low-frequency carbon radio recombination lines from within the Orion molecular cloud complex observed at 99-129 MHz. These tentative detections include one alpha transition and one beta transition over three locations and are located within the diffuse regions of dust observed in the infrared at 100umm, the Halpha emission detected in the optical, and the synchrotron radiation observed in the radio. With these observations, we are able to study the radiation mechanism transition from collisionally pumped to radiatively pumped within the HII regions of the Orion molecular cloud complex.

[25]
Title: Implementing Tidal and Gravitational Wave Energy Losses in Few-body Codes: A Fast and Easy Drag Force Model
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present a drag force model for evolving chaotic few-body interactions with the inclusion of orbital energy losses, such as tidal dissipation and gravitational wave (GW) emission. The main effect from such losses is the formation of two-body captures, that for compact objects result in GW mergers, and for stars lead to either compact binaries, mergers or disruptions. Studying the inclusion of energy loss terms in few-body interactions is therefore likely to be important for modeling and understanding the variety of transients that soon will be observed by current and upcoming surveys. However, including especially tides in few-body codes has been shown to be technically difficult and computationally heavy, which has lead to very few systematic tidal studies. In this paper we derive a drag force term that can be used to model the effects from tidal, as well as other, energy losses in few-body interactions, if the two-body orbit averaged energy loss is known a priori. This drag force model is very fast to evolve, and gives results in agreement with other approaches, including the impulsive and affine tide approximations.

[26]
Title: A WISE Survey of New Star Clusters in the Central Plane Region of the Milky Way
Comments: 29 pages, 16 figures, accepted to ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the discovery of new star clusters in the central plane region ($|l|<30\deg$ and $|b|<6\deg$) of the Milky Way. In order to overcome the extinction problem and the spatial limit of previous surveys, we use the Wide-field Infrared Survey Explorer (WISE) data to find clusters. We also use other infrared survey data in the archive for additional analysis. We find 923 new clusters, of which 202 clusters are embedded clusters. These clusters are concentrated toward the Galactic plane and show a symmetric distribution with respect to the Galactic latitude. The embedded clusters show a stronger concentration to the Galactic plane than the non-embedded clusters. The new clusters are found more in the first Galactic quadrant, while previously known clusters are found more in the fourth Galactic quadrant. The spatial distribution of the combined sample of known clusters and new clusters is approximately symmetric with respect to the Galactic longitude. We estimate reddenings, distances, and relative ages of the 15 class A clusters using theoretical isochrones. Ten of them are relatively old (age $>800$ Myr) and five are young (age $\approx4$ Myr).

[27]
Title: Galaxy interactions in loose galaxy groups: KAT-7 and VLA HI Observations of the IC 1459 group
Comments: 4 pages. Submitted to Astronomy and Astrophysics Letters
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We report on the results from deep HI observations, performed with the Karoo Array Telescope and with the Karl G. Jansky Very Large Array of the loose galaxy group centred on the early-type galaxy IC 1459. The main result from our observations is the detection of a nearly continuous, 500-kpc long HI tail which crosses the entire group. Earlier observations with the Australia Telescope Compact Array had shown the presence of a large HI tail in this galaxy group, but because of the much larger coverage of the new data, the full extent of this tail is now visible. The HI mass of this structure is 3.1 +- 0.3 10^9 Msun . Based on its morphology and kinematics, we conclude that the tail consists of gas stripped from NGC 7418 through tidal interactions, with ram-pressure affects playing at most a minor role. Optical images of the IC 1459 group do not show many indications that galaxy interactions are common in this group. The HI data reveal a very different picture and show that almost all gas-rich galaxies in the IC 1459 group have a distorted HI distribution indicating that many interactions are occurring in this group. This high number of interactions shows that the processes that drive galaxy transformation are also occurring in fairly loose galaxy groups.

[28]
Title: Rotation and magnetism in intermediate mass stars
Comments: 13 pages, 16 figures, accepted by MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Rotation and magnetism are increasingly recognized as important phenomena in stellar evolution. Surface magnetic fields from a few to $20{,}000\,$G have been observed and models have suggested that magnetohydrodynamic transport of angular momentum and chemical composition could explain the peculiar composition of some stars. Stellar remnants such as white dwarfs have been observed with fields from a few to more than $10^{9}\,$G. We investigate the origin of and the evolution, on thermal and nuclear rather than dynamical time-scales, of an averaged large-scale magnetic field throughout a star's life and its coupling to stellar rotation. Large-scale magnetic fields sustained until late stages of stellar evolution with conservation of magnetic flux could explain the very high fields observed in white dwarfs. We include these effects in the Cambridge stellar evolution code using three time-dependant advection-diffusion equations coupled to the structural and composition equations of stars to model the evolution of angular momentum and the two components of the magnetic field. We present the evolution in various cases for a $3\rm\,M_{\odot}$ star from the beginning to the late stages of its life. Our particular model assumes that turbulent motions, including convection, favour small-scale field at the expense of large-scale field. As a result the large-scale field concentrates in radiative zones of the star and so is exchanged between the core and the envelope of the star as it evolves. The field is sustained until the end of the asymptotic giant branch, when it concentrates in the degenerate core.

[29]
Title: Superconformal Subcritical Hybrid Inflation
Authors: Koji Ishiwata
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

We consider D-term hybrid inflation in the framework of superconformal supergravity. In part of the parameter space, inflation continues for subcritical inflaton field value. Consequently, a new type of inflation emerges, which gives predictions for the scalar spectral index and the tensor-to-scalar ratio that are consistent with the Planck 2015 results. The potential in the subcritical regime is found to have a similar structure to one in the simplest class of superconformal alpha attractors.

[30]
Title: Transition region bright dots in active regions observed by the Interface Region Imaging Spectrograph
Comments: 4 pages, 4 figures, publication in AIP Conference Proceedings
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The Interface Region Imaging Spectrograph (IRIS) reveals numerous small-scale (sub-arcsecond) brightenings that appear as bright dots sparkling the solar transition region in active regions. Here, we report a statistical study on these transition region bright dots. We use an automatic approach to identify 2742 dots in a Si IV raster image. We find that the average spatial size of the dots is 0.8 arcsec$^2$ and most of them are located in the faculae area. Their Doppler velocities obtained from the Si IV 1394 {\AA} line range from -20 to 20 km/s. Among these 2742 dots, 1224 are predominantly blue-shifted and 1518 are red-shifted. Their nonthermal velocities range from 4 to 50 km/s with an average of 24 km/s. We speculate that the bright dots studied here are small-scale impulsive energetic events that can heat the active region corona.

[31]
Title: Bayesian Inference on the Radio-quietness of Gamma-ray Pulsars
Comments: 14 pages, 6 figures, 1 table, accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We demonstrate for the first time using a robust Bayesian approach to analyse the populations of radio-quiet (RQ) and radio-loud (RL) gamma-ray pulsars. We quantify their differences and obtain their distributions of the radio-cone opening half-angle $\delta$ and the magnetic inclination angle $\alpha$ by Bayesian inference. In contrast to the conventional frequentist point estimations that might be non-representative when the distribution is highly skewed or multi-modal, which is often the case when data points are scarce, Bayesian statistics displays the complete posterior distribution that the uncertainties can be readily obtained regardless of the skewness and modality. We found that the spin period, the magnetic field strength at the light cylinder, the spin-down power, the gamma-ray-to-X-ray flux ratio, and the spectral curvature significance of the two groups of pulsars exhibit significant differences at the 99\% level. Using Bayesian inference, we are able to infer the values and uncertainties of $\delta$ and $\alpha$ from the distribution of RQ and RL pulsars. We found that $\delta$ is between $10^\circ$ and $35^\circ$ and the distribution of $\alpha$ is skewed towards large values.

[32]
Title: Relativistic jet feedback III: feedback on gas disks
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA)

We study the interactions of a relativistic jet with a dense turbulent gaseous disk of radius $\sim 2$ kpc. We have performed a suite of simulations with different mean density, jet power and orientation. Our results show that: A) the relativistic jet couples strongly with the gas in the inner kpc, creating a cavity and launching outflows. B) The high pressure bubble inflated by the jet and its back-flow compresses the disk at the outer edges, driving inflows within the disk. C) Jets inclined towards the disk couple more strongly with the disk and launch sub-relativistic, wide-angle outflows along the minor axis. D) Shocks driven directly by the jet and the jet-driven energy bubble raise the velocity dispersion throughout the disk by several times its initial value. E) Compression by the jet-driven shocks can enhance the star formation rate in the disk, especially in a ring-like geometry close to the axis. However, enhanced turbulent dispersion in the disk also leads to quenching of star formation. Whether positive or negative feedback dominates depends on jet power, ISM density, jet orientation with respect to the disc, and the time-scale under consideration. Qualitatively, our simulations compare favourably with kinematic and morphological signatures of several observed galaxies such as NGC 1052, NGC 3079, 3C 326 and 3C 293.

[33]
Title: A Statistical Study of the Magnetic Imprints of X-Class Flares using SDO/HMI Vector Magnetograms
Comments: 8 pages, 4 figures, 1 table, submitted to The Astrophysical Journal Letters (ApJL)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

Magnetic imprints, the rapid and irreversible evolution of photospheric magnetic fields as a feedback from flares in the corona, have been confirmed by many previous studies. These studies showed that the horizontal field will permanently increase near the polarity inversion line (PIL) after eruptions, indicating that a more horizontal topology of photospheric magnetic field will be reconstructed. In this study, we analyze 17 near-disk X-class flares in 13 active regions (ARs) with heliographic angle no greater than 45 degrees since the launch of the Solar Dynamics Observatory (SDO). We find that confined flares without or with very weak CMEs tend to show very weak magnetic imprints on the photosphere. The imprint regions of the horizontal field could locate not only near the PIL but also near sunspot umbrae with strong vertical fields. Making use of the observed CME mass and speed, we find that the CMEs with larger momentums will bring into stronger magnetic imprints. Furthermore, a linear relationship, with a confidence coefficient 0.82, between the CME momentum and the change of Lorentz force is revealed. Based on that, we quantify the back reaction time to be 336 s, which could be further applied to independently estimate the CME mass.

[34]
Title: Predicting the Neutral Hydrogen Content of Galaxies From Optical Data Using Machine Learning
Comments: 16 pages, 11 figures, 1 table
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We develop a machine learning-based framework to predict the HI content of galaxies using more straightforwardly observable quantities such as optical photometry and environmental parameters. We train the algorithm on z=0-2 outputs from the Mufasa cosmological hydrodynamic simulation, which includes star formation, feedback, and a heuristic model to quench massive galaxies that yields a reasonable match to a range of survey data including HI. We employ a variety of machine learning methods (regressors), and quantify their performance using the root mean square error ({\sc rmse}) and the Pearson correlation coefficient (r). Considering SDSS photometry, 3$^{rd}$ nearest neighbor environment and line of sight peculiar velocities as features, we obtain r $> 0.8$ accuracy of the HI-richness prediction, corresponding to {\sc rmse}$<0.3$. Adding near-IR photometry to the features yields some improvement to the prediction. Compared to all the regressors, random forest shows the best performance, with r $>0.9$ at $z=0$, followed by a Deep Neural Network with r $>0.85$. All regressors exhibit a declining performance with increasing redshift, which limits the utility of this approach to $z\la 1$, and they tend to somewhat over-predict the HI content of low-HI galaxies which might be due to Eddington bias in the training sample. We test our approach on the RESOLVE survey data. Training on a subset of RESOLVE data, we find that our machine learning method can reasonably well predict the HI-richness of the remaining RESOLVE data, with {\sc rmse}$\sim0.28$. When we train on mock data from Mufasa and test on RESOLVE, this increases to {\sc rmse}$\sim0.45$. Our method will be useful for making galaxy-by-galaxy survey predictions and incompleteness corrections for upcoming HI 21cm surveys such as the LADUMA and MIGHTEE surveys on MeerKAT, over regions where photometry is already available.

[35]
Title: Treatment of isomers in nucleosynthesis codes
Journal-ref: International Journal of Modern Physics A, Vol. 33 (2018) 1843011 (open access)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)

The decay properties of long-lived excited states (isomers) can have a significant impact on the destruction channels of isotopes under stellar conditions. In sufficiently hot environments, the population of isomers can be altered via thermal excitation or de-excitation. If the corresponding lifetimes are of the same order of magnitude as the typical time scales of the environment, the isomers have to be the treated explicitly. We present a general approach to the treatment of isomers in stellar nucleosynthesis codes and discuss a few illustrative examples. The corresponding code is available online at this http URL

[36]
Title: Detection of Alpha Centauri at radio wavelengths: chromospheric emission and search for star-planet interaction
Comments: Submitted to MNRAS, 9 pages, 8 Figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

At radio wavelengths, solar type stars emit thermal free-free and gyroresonance, gyrosynchrotron, and impulsive coherent emission. Thermal free-free emission originates at layers where the optical depth is close to unit, while high brightness temperature, variable emission, can be due to flares via gyrosynchrotron emission. We observed the alf Cen system with the Australian Telescope Compact Array at 2 GHz for three days and 17 GHz for one day. Both stars have been detected at 17 GHz, while only an upper limit has been obtained at low frequency despite the longest integration time. The brightness temperatures are consistent with the temperature of the upper chromosphere of the Sun. Inverting the formulae of the free-free emission, the average electron density of the plasma has been inferred. The same procedure was applied to the data in the millimetre recently taken with ALMA. A comparison with the atmospheric solar models reveals a higher level of activity in alf Cen B, even if still at quiescent level. The non detection at low frequency allow us to put a lower limit in the filling factor of active regions. The claimed detection of an Earth size planet in close orbit to alf Cen B, although doubtful, open the opportunity to check the existence of Star-Planet Magnetic Interaction (SPMI). This could trigger Auroral Radio Emission due to Electron Cyclotron Maser in the stellar corona, similar to the Jupiter-Io interaction, which is very intense, polarized and highly beamed. However, no hints of SPMI has been found.

[37]
Title: Searching for a dipole anisotropy on acceleration scale with 147 rotationally supported galaxies
Comments: 12 pages, 3 figures, 1 table
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We report a dipole anisotropy on acceleration scale $g_{\dag}$ in local universe with 147 rotationally supported galaxies. We find that a monopole and dipole correction for the radial acceleration relation can better describe the SPARC data set. The monopole term is negligible but the dipole magnitude is significant. It is also found that the dipole anisotropy is mostly induced by spatial variation of the acceleration scale. The magnitude of $g_{\dag}$-dipole reaches up to $0.25\pm0.04$, and its direction is aligned to $(l,b) = (171.40^{\circ}\pm7.34^{\circ}, -15.30^{\circ}\pm4.82^{\circ})$, which is very close to the maximum anisotropy direction from the hemisphere comparison method. Furthermore, robust check shows that the dipole anisotropy couldn't be reproduced by isotropic mock data set. If the anisotropy signal is real, it may provide a new method to test the cosmological anisotropy.

[38]
Title: NuSTAR Detection of X-Ray Heating Events in the Quiet Sun
Comments: Accepted for publication in ApJL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

The explanation of the coronal heating problem potentially lies in the existence of nanoflares, numerous small-scale heating events occuring across the whole solar disk. In this paper, we present the first imaging spectroscopy X-ray observations of three quiet Sun flares during the NuSTAR solar campaigns on 2016 July 26 and 2017 March 21, concurrent with SDO/AIA observations. Two of the three events showed time lags of a few minutes between peak X-ray and extreme ultraviolet (EUV) emissions. Isothermal fits with rather low temperatures in the range $3.2-4.1$ MK and emission measures of $(0.6-15)\times10^{44} \textrm{ cm}^{-3}$ describe their spectra well, resulting in thermal energies in the range $(2-6)\times10^{26}\textrm{ ergs}$. NuSTAR spectra did not show any signs of a nonthermal or higher temperature component. However, since the estimated upper limits of (hidden) nonthermal energy are comparable to the thermal energy estimates, the lack of a nonthermal component in the observed spectra is not a constraining result. The estimated GOES classes from the fitted values of temperature and emission measure fall between $1/1000 \textrm{ and } 1/100$ A class level, making them 8 orders of magnitude fainter in soft X-ray flux than the largest solar flares.

[39]
Title: The Propagation of Cosmic Rays from the Galactic Wind Termination Shock: Back to the Galaxy?
Comments: 16 pages, 16 figures, 1 table, submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Although several theories for the origin of cosmic rays in the region between the spectral knee' and ankle' exist, this problem is still unsolved. A variety of observations suggest that the transition from Galactic to extragalactic sources occurs in this energy range. In this work we examine whether a Galactic wind which eventually forms a termination shock far outside the Galactic plane can contribute as a possible source to the observed flux in the region of interest. Previous work by Bustard et al. (2017) estimated that particles can be accelerated up to energies above the knee' up to $R_\mathrm{max} = 10^{16}$ eV for parameters drawn from a model of a Milky Way wind (Everett et al. 2017). A remaining question is whether the accelerated cosmic rays can propagate back into the Galaxy. To answer this crucial question, we simulate the propagation of the cosmic rays using the low energy extension of the CRPropa framework, based on the solution of the transport equation via stochastic differential equations. The setup includes all relevant processes, including three-dimensional anisotropic spatial diffusion, advection, and corresponding adiabatic cooling. We find that, assuming realistic parameters for the shock evolution, a possible Galactic termination shock can contribute significantly to the energy budget in the `knee' region and above. We estimate the resulting produced neutrino fluxes and find them to be below measurements from IceCube and limits by KM3NeT.

[40]
Title: Observations contradict galaxy size and surface brightness predictions that are based on the expanding universe hypothesis
Authors: Eric J. Lerner
Journal-ref: Monthly Notices of the Royal Astronomical Society, sty728 (March 22, 2018)
Subjects: Astrophysics of Galaxies (astro-ph.GA)

In a non-expanding universe surface brightness is independent of distance or redshift, while in an expanding universe it decreases rapidly with both. Similarly, for objects of the same luminosity, the angular radius of an object in a non-expanding universe declines with redshift, while in an expanding universe this radius increases for redshifts z>1.25. The author and colleagues have previously shown that data for the surface brightness of disk galaxies are compatible with a static universe with redshift linearly proportional to distance at all z (SEU hypothesis). In this paper we examine the more conventional hypothesis that the universe is expanding, but that the actual radii of galaxies of a given luminosity increase with time (decrease with z), as others have proposed. We show that the radii data for both disk and elliptical galaxies are incompatible with any of the published size-evolution predictions based on an expanding universe. We find that all the physical mechanisms proposed for size evolution, such as galaxy mergers, lead to predictions that are in quantitative contradiction with either the radius data or other data sets, such as the observed rate of galaxy mergers. In addition, we find that when the effect of telescope resolution is taken into account, the r-z relationships for disk and elliptical galaxies are identical. Both are excellently fit by SEU predictions. An overall comparison of cosmological models requires examining all available data-sets, but for this data-set there is a clear contradiction of predictions based on an expanding universe hypothesis.

[41]
Title: The correlation between the total magnetic flux and the total jet power
Authors: E. Nokhrina
Comments: 12 pages, 2 figures, 1 table
Journal-ref: Frontiers in Astronomy and Space Sciences, 4, 63 (2017)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Magnetic field threading a black hole ergosphere is believed to play the key role in both driving the powerful relativistic jets observed in active galactic nuclei and extracting the rotational energy from a black hole via Blandford-Znajek process. The magnitude of magnetic field and the magnetic flux in the vicinity of a central black hole is predicted by theoretical models. On the other hand, the magnetic field in a jet can be estimated through measurements of either the core shift effect or the brightness temperature. In both cases the obtained magnetic field is in the radiating domain, so its direct application to the calculation of the magnetic flux needs some theoretical assumptions. In this paper we address the issue of estimating the magnetic flux contained in a jet using the measurements of a core shift effect and of a brightness temperature for the jets, directed almost at the observer. The accurate account for the jet transversal structure allow us to express the magnetic flux through the observed values and an unknown rotation rate of magnetic surfaces. If we assume the sources are in a magnetically arrested disk state, the lower limit for the rotation rate can be obtained. On the other hand, the flux estimate may be tested against the total jet power predicted by the electromagnetic energy extraction model. The resultant expression for power depends logarithmically weakly on an unknown rotation rate. We show that the total jet power estimated through the magnetic flux is in good agreement with the observed power. We also obtain the extremely slow rotation rates, which may be an indication that the majority of the sources considered are not in the magnetically arrested disk state.

[42]
Title: A fresh look into the interacting dark matter scenario
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The elastic scattering between dark matter particles and photons represents an attractive possibility to solve a number of discrepancies between observations and standard cold dark matter predictions, as the induced collisional damping would imply a suppression of small-scale structures. We consider this scenario and confront it with measurements of the ionization history of the Universe at several redshifts and with recent estimates of the counts of Milky Way satellite galaxies. We derive a a conservative upper bound on the dark matter-photon elastic scattering cross section of $\sigma_{\gamma \rm{DM}} < 8 \times 10^{-10} \, \sigma_T \, \left(m_{\rm DM}/{\rm GeV}\right)$ at $95\%$~CL, about one order of magnitude tighter than previous findings. Due to the strong degeneracies with astrophysical parameters, the bound on the dark matter-photon scattering cross section derived here is driven by the estimate of the number of Milky Way satellite galaxies. Finally, we also argue that future 21~cm probes could help in disentangling among possible non-cold dark matter candidates, such as interacting and warm dark matter scenarios.

[43]
Title: On the age of the Nele asteroid family
Comments: 11 pages, 12 figures, accepted for publication on MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The Nele group, formerly known as the Iannini family, is one of the youngest asteroid families in the main belt. Previously, it has been noted that the pericenter longitudes $\varpi$ and nodal longitudes $\Omega$ of its largest member asteroids are clustered at the present time, therefore suggesting that the collisional breakup of parent body must have happened recently. Here we verify this conclusion by detailed orbit-propagation of a synthetic Nele family and show that the current level of clustering of secular angles of the largest Nele family members requires an approximate age limit of $4.5$ Myr. Additionally, we make use of an updated and largely extended Nele membership to obtain, for the first time, an age estimate of this family using the Backward Integration Method (BIM). Convergence of the secular angles in a purely gravitational model and in a model including the non-gravitational forces caused by the Yarkovsky effect are both compatible with an age younger than $7$ Myr. More accurate determination of the Nele family age would require additional data about the spin state of its members.

[44]
Title: Opening PANDORA's box: APEX observations of CO in PNe
Comments: 24 pages, accepted for publication in the A&A Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Context. Observations of molecular gas have played a key role in developing the current understanding of the late stages of stellar evolution. Aims. The survey Planetary nebulae AND their cO Reservoir with APEX (PANDORA) was designed to study the circumstellar shells of evolved stars with the aim to estimate their physical parameters. Methods. Millimetre carbon monoxide (CO) emission is the most useful probe of the warm molecular component ejected by low- to intermediate-mass stars. CO is the second-most abundant molecule in the Universe, and the millimeter transitions are easily excited, thus making it particularly useful to study the mass, structure, and kinematics of the molecular gas. We present a large survey of the CO (J = 3 - 2) line using the Atacama Pathfinder EXperiment (APEX) telescope in a sample of 93 proto-planetary nebulae and planetary nebulae. Results. CO (J = 3 - 2) was detected in 21 of the 93 objects. Conclusions. CO (J = 3 - 2) was detected in all 4 observed pPNe (100%), 15 of the 75 PNe (20%), one of the 4 wide binaries (25%), and in 1 of the 10 close binaries (10%). Using the CO (J = 3 - 2) line, we estimated the column density and mass of each source.

[45]
Title: Current Constraints on Anisotropic and Isotropic Dark Energy Models Using Gaussian Processes
Comments: 9 pages, 13 figures, 6 tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We use Gaussian processes in combination with MCMC method to place constraints on cosmological parameters of three dark energy models including flat and curved FRW and Bianchi type I spacetimes. Recently compiled 36 measurements of the Hubble parameter $H(z)$ in the redshifts intermediate $0.07\leqslant z \leqslant 2.36$ have been used in our nonparametric reconstruction of the cosmological parameters. Moreover, we use these models to estimate the redshift of the deceleration-acceleration transition. We consider two Gaussian priors for current value of the Hubble constant i.e $H_{0}=73\pm1.74 (68\pm 2.8)$ km/s/Mpc to to investigate the effect of the assumed $H_{0}$ on our parameters estimations. For statistical analysis we use NUTS sampler which is an extension of Hamiltonian Monte Carlo algorithm to generate MCMC chains for parameters of dark energy models. In general, when we compared our results with 9 years WMAP as well as Planck 2016 Collaboration, we found that Bianchi type I model is slightly fits better to the observational Hubble data with respect to the flat FRW model.

[46]
Title: Weak lensing peak statistics in the era of large scale cosmological surveys
Weak lensing peak counts are a powerful statistical tool for constraining cosmological parameters. So far, this method has been applied only to surveys with relatively small areas, up to several hundred square degrees. As future surveys will provide weak lensing datasets with size of thousands of square degrees, the demand on the theoretical prediction of the peak statistics will become heightened. In particular, large simulations of increased cosmological volume are required. In this work, we investigate the possibility of using simulations generated with the fast Comoving-Lagrangian acceleration (COLA) method, coupled to the convergence map generator Ufalcon, for predicting the peak counts. We examine the systematics introduced by the COLA method by comparing it with a full TreePM code. We find that for a 2000 deg$^2$ survey, the systematic error is much smaller than the statistical error. This suggests that the COLA method is able to generate promising theoretical predictions for weak lensing peaks. We also examine the constraining power of various configurations of data vectors, exploring the influence of splitting the sample into tomographic bins and combining different smoothing scales. We find the combination of smoothing scales to have the most constraining power, improving the constraints on the $S_8$ amplitude parameter by at least 40% compared to a single smoothing scale, with tomography brining only limited increase in measurement precision.