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J.P. Magué & B. Ménard



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[1]  arXiv:1409.5120 [pdf, ps, other]
Title: A new prescription for the random magnetic field of the Milky Way
Comments: 8 pages, 10 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

We present a new prescription for the small-scale magnetic field of the Milky Way and complement existing models for the total Galactic magnetic field. In particular, we extend the random and striated magnetic field components of the Jansson & Farrar (JF12) model and investigate the characteristics of random magnetic fluctuations. Thereby the small-scale magnetic field is modelled by Gaussian random fields using a random magnetic field power spectrum. We update the spatial distribution of Galactic cosmic ray electron density by a recent GALPROP model.
We derive full-sky projections of the total and polarized synchrotron intensity as well as the Faraday rotation measure distribution of our model and compare to real data. We obtain good agreement to the WMAP7 22 GHz polarized and total intensity emission maps and we retrieve improved fits to Galactic foreground rotation measure maps and power spectra of Oppermann et al. Our new prescription significantly complements previous models of the GMF and reveals implications for future studies on the deflection of ultra high energy cosmic rays (UHECR).

[2]  arXiv:1409.5121 [pdf, ps, other]
Title: Formation and evolution of nuclear star clusters with in-situ star-formation: Nuclear cores and age segregation
Comments: Comments are welcome
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Nuclear stellar cluster (NSCs) are known to exist around massive black holes (MBHs) in galactic nuclei. Two formation scenarios were suggested for their origin: (1) Build-up of NSCs from consecutive infall of stellar cluster and (2) Continuous in-situ star-formation. Though the cluster-infall scenario has bees extensively studied in recent years, the in-situ formation scenario have been hardly explored. Here we use Fokker-Planck (FP) calculations to study the effects of star formation on the build-up of NSCs and its implications for their long term evolution and their resulting structure. We use the FP equation to describe the evolution of several stellar populations, and add appropriate source terms to account for the effects of newly formed stars. We show that continuous star-formation even 1-2 pc away from the MBH can lead to the build-up of an NSC with properties similar to those of the Milky-way NSC. We also find that the general structure of the old stellar population in the NSC with in-situ star-formation could be very similar to the steady-state Bahcall-Wolf cuspy structure. However, its younger stellar population do not yet achieve a steady state. In particular, formed/evolved NSCs with in-situ star-formation contain differential age-segregated stellar populations which are not yet fully mixed. Younger stellar populations formed in the outer regions of the NSC have a cuspy structure towards the NSC outskirts, while showing a core-like distribution inwards; with younger populations having larger core sizes. In principal, such a structure can give rise to an apparent core-like radial distribution of younger (up to 2-3 Gyrs) stars, as observed in the Galactic center. Such an NSC still preserves an underlying stellar cusp of older stars, that can be potentially be missed by current observations of red-giants.

[3]  arXiv:1409.5122 [pdf, ps, other]
Title: The host galaxies of X-ray selected Active Galactic Nuclei to z=2.5: Structure, star-formation and their relationships from CANDELS and Herschel/PACS
Comments: 25 pages (double-column), 17 Figures, under review at A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We study the relationship between the structure and star-formation rate (SFR) of X-ray selected low and moderate luminosity active galactic nuclei (AGNs) in the two Chandra Deep Fields, using Hubble Space Telescope imaging from the Cosmic Assembly Near Infrared Extragalactic Legacy Survey (CANDELS) and deep far-infrared maps from the PEP+GOODS-Herschel survey. We derive detailed distributions of structural parameters and FIR luminosities from carefully constructed control samples of galaxies, which we then compare to those of the AGNs. At z~1, AGNs show slightly diskier light profiles than massive inactive (non-AGN) galaxies, as well as modestly higher levels of gross galaxy disturbance (as measured by visual signatures of interactions and clumpy structure). In contrast, at z~2, AGNs show similar levels of galaxy disturbance as inactive galaxies, but display a red central light enhancement, which may arise due to a more pronounced bulge in AGN hosts or due to extinguished nuclear light. We undertake a number of tests of these alternatives, but our results do not strongly favour one interpretation over the other. The mean SFR and its distribution among AGNs and inactive galaxies are similar at z>1.5. At z<1, however, clear and significant enhancements are seen in the SFRs of AGNs with bulge-dominated light profiles. These trends suggest an evolution in the relation between nuclear activity and host properties with redshift, towards a minor role for mergers and interactions at z>1.5.

[4]  arXiv:1409.5124 [pdf, ps, other]
Title: Binary Black Hole Accretion During Inspiral and Merger
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present the results of 2D, moving mesh, viscous hydrodynamical simulations of accretion onto merging supermassive black hole (SMBH) binaries. We include viscous heating, shock heating, and radiative cooling, and simulate the transition from the "pre-decoupling" epoch, where the inspiral timescale is longer than the viscous timescale, to the "post-decoupling" epoch, where the inspiral timescale is shorter than the viscous timescale. We find that there is no abrupt halt to the accretion at decoupling, but rather the accretion shows a slow decay, with significant accretion well after the expected decoupling. Moreover, we find that the luminosity in X-rays is significantly higher prior to the merger, as orbital energy from the SMBH binary is converted to heat via strong shocks inside the cavity, and radiated away. Following the merger, the cavity refills viscously and the accretion rate relaxes to the Shakura-Sunyaev value, while the X-ray luminosity drops as the shocks quickly dissipate.

[5]  arXiv:1409.5126 [pdf, ps, other]
Title: Formation of S0 galaxies through mergers. Bulge-disc structural coupling resulting from major mergers
Comments: 23 pages, accepted for publication in Astronomy and Astrophysics
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Observations reveal a strong structural coupling between bulge and disc in S0 galaxies, which seems difficult to explain if they have formed from supposedly catastrophic events such as major mergers. We face this question by quantifying the bulge-disc coupling in dissipative simulations of major and minor mergers that result in realistic S0s. We have studied the dissipative N-body binary merger simulations from the GalMer database that give rise to realistic, relaxed E/S0 and S0 remnants (67 major and 29 minor mergers). We simulate surface brightness profiles of these S0-like remnants in the K-band, mimicking typical observational conditions, to perform bulge-disc decompositions analogous to those carried out in real S0s. The global bulge-disc structure of these remnants has been compared with real data, and they distribute in the B/T - r_e - h_d parameter space consistently with real bright S0s, where B/T is the bulge-to-total luminosity ratio, r_e is the bulge effective radius, and h_d is the disc scalelength. Major mergers can rebuild a bulge-disc coupling in the remnants after having destroyed the structures of the progenitors, whereas minor mergers directly preserve them. Remnants exhibit B/T and r_e/h_d spanning a wide range of values, and their distribution is consistent with observations. Many remnants have bulge Sersic indices ranging 1<n<2, flat appearance, and contain residual star formation in embedded discs, a result which agrees with the presence of pseudobulges in real S0s. Contrary to the popular view, mergers (and in particular, major events) can result in S0 remnants with realistically coupled bulge-disc structures in less than ~3 Gyr. In conclusion, the bulge-disc coupling and the presence of pseudobulges in real S0s cannot be used as an argument against the possible major-merger origin of these galaxies.

[6]  arXiv:1409.5128 [pdf, ps, other]
Title: Maximizing the ExoEarth Candidate Yield from a Future Direct Imaging Mission
Comments: Accepted for publication in ApJ; 47 pages, 17 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

ExoEarth yield is a critical science metric for future exoplanet imaging missions. Here we estimate exoEarth candidate yield using single visit completeness for a variety of mission design and astrophysical parameters. We review the methods used in previous yield calculations and show that the method choice can significantly impact yield estimates as well as how the yield responds to mission parameters. We introduce a method, called Altruistic Yield Optimization, that optimizes the target list and exposure times to maximize mission yield, adapts maximally to changes in mission parameters, and increases exoEarth candidate yield by up to 100% compared to previous methods. We use Altruistic Yield Optimization to estimate exoEarth candidate yield for a large suite of mission and astrophysical parameters using single visit completeness. We find that exoEarth candidate yield is most sensitive to telescope diameter, followed by coronagraph inner working angle, followed by coronagraph contrast, and finally coronagraph contrast noise floor. We find a surprisingly weak dependence of exoEarth candidate yield on exozodi level. Additionally, we provide a quantitative approach to defining a yield goal for future exoEarth-imaging missions.

[7]  arXiv:1409.5129 [pdf, ps, other]
Title: Johannes and the seven dwarfs: Kepler detection of low-level day-timescale periodic photometric variations in white dwarfs
Comments: MNRAS, submitted
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We make use of the high photometric precision of Kepler to search for periodic variations among 14 normal (DA- and DB-type, likely non-magnetic) hot white dwarfs (WDs) observed by the mission. In seven of the WDs, we detect periodic, ~2 hr to 10 d, variations, with semi-amplitudes of 40 to 2000 ppm, lower than ever seen in WDs. We consider various explanations for the observed variations: WD rotation combined with magnetic cool spots; rotation combined with magnetic dichroism; rotation combined with hot spots from an interstellar-medium accretion flow, channeled onto weak magnetic poles; transits by size ~50-200 km objects; relativistic beaming due to reflex motion caused by a cool companion WD; or reflection/re-radiation of the primary WD light by a brown-dwarf companion, or by a giant planet of about Jupiter radius, undergoing illumination phases as it orbits the WD. Each of these mechanisms could be behind some of the variable WDs, but could not be responsible for all seven variable cases. Alternatively, the periodicity may arise from UV metal-line opacity, associated with accretion of rocky material, a phenomenon seen in ~50% of hot WDs. Slightly non-uniform UV opacity, combined with WD rotation and fluorescent optical re-emission of the absorbed UV energy, could potentially explain our findings. Even if reflection of the WD light by a planet is the cause in only a few of the seven cases, it would imply that hot Jupiters are very common around WDs. Alternatively, if some of the rotation-related mechanisms are at work, it would indicate that normal WDs rotate as slowly as do peculiar WDs, the only kind for which precise rotation measurements have been possible to date. Followup observations for this sample, and the larger numbers of additional WDs now being monitored as part of the K2 Kepler mission extension, will soon discriminate among these possibilities.

[8]  arXiv:1409.5130 [pdf, ps, other]
Title: The impact of spurious shear on cosmological parameter estimates from weak lensing observables
Comments: 18 pages, 12 figures, 8 tables. Submitted to PRD
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Residual errors in shear measurements, after corrections for instrument systematics and atmospheric effects, can impact cosmological parameters derived from weak lensing observations. Here we combine convergence maps from our suite of ray-tracing simulations with random realizations of spurious shear with a power spectrum estimated for the LSST instrument. This allows us to quantify the errors and biases of the triplet $(\Omega_m,w,\sigma_8)$ derived from the power spectrum (PS), as well as from three different sets of non-Gaussian statistics of the lensing convergence field: Minkowski functionals (MF), low--order moments (LM), and peak counts (PK). Our main results are: (i) We find an order of magnitude smaller biases from the PS than in previous work. (ii) The PS and LM yield biases much smaller than the morphological statistics (MF, PK). (iii) For strictly Gaussian spurious shear with integrated amplitude as low as its current estimate of $\sigma^2_{sys}\approx 10^{-7}$, biases from the PS and LM would be unimportant even for a survey with the statistical power of LSST. However, we find that for surveys larger than $\approx 100$ deg$^2$, non-Gaussianity in the noise (not included in our analysis) will likely be important and must be quantified to assess the biases. (iv) The morphological statistics (MF,PK) introduce important biases even for Gaussian noise, which must be corrected in large surveys. The biases are in different directions in $(\Omega_m,w,\sigma_8)$ parameter space, allowing self-calibration by combining multiple statistics. Our results warrant follow-up studies with more extensive lensing simulations and more accurate spurious shear estimates.

[9]  arXiv:1409.5132 [pdf, ps, other]
Title: Spectroscopic Study of the Open Cluster NGC 6811
Comments: 18 pages, 11 tables, 7 figures, accepted for MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The NASA space telescope Kepler has provided unprecedented time-series observations which have revolutionised the field of asteroseismology, i.e. the use of stellar oscillations to probe the interior of stars. The Kepler-data include observations of stars in open clusters, which are particularly interesting for asteroseismology. One of the clusters observed with Kepler is NGC 6811, which is the target of the present paper. However, apart from high-precision time-series observations, sounding the interiors of stars in open clusters by means of asteroseismology also requires accurate and precise atmospheric parameters as well as cluster membership indicators for the individual stars. We use medium-resolution (R~25,000) spectroscopic observations, and three independent analysis methods, to derive effective temperatures, surface gravities, metallicities, projected rotational velocities and radial velocities, for 15 stars in the field of the open cluster NGC 6811. We discover two double-lined and three single-lined spectroscopic binaries. Eight stars are classified as either certain or very probable cluster members, and three stars are classified as non-members. For four stars, cluster membership could not been assessed. Five of the observed stars are G-type giants which are located in the colour-magnitude diagram in the region of the red clump of the cluster. Two of these stars are surely identified as red clump stars for the first time. For those five stars, we provide chemical abundances of 31 elements. The mean radial-velocity of NGC 6811 is found to be +6.68$\pm$0.08 km s$^{-1}$ and the mean metallicity and overall abundance pattern are shown to be very close to solar with an exception of Ba which we find to be overabundant.

[10]  arXiv:1409.5134 [pdf, ps, other]
Title: Deep Thermal Infrared Imaging of HR 8799 bcde: New Atmospheric Constraints and Limits on a Fifth Planet
Comments: 18 pages, 6 Tables, and 9 Figures. Fig. 1a is the key figure. Accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We present new $L^\prime$ (3.8 $\mu m$) and Br-$\alpha$ (4.05 $\mu m$) data and reprocessed archival $L^\prime$ data for the young, planet-hosting star HR 8799 obtained with Keck/NIRC2, VLT/NaCo and Subaru/IRCS. We detect all four HR 8799 planets in each dataset at a moderate to high signal-to-noise (SNR $\gtrsim$ 6-15). We fail to identify a fifth planet, "HR 8799 f", at $r$ $<$ 15 $AU$ at a 5-$\sigma$ confidence level: one suggestive, marginally significant residual at 0.2" is most likely a PSF artifact. Assuming companion ages of 30 $Myr$ and the Baraffe (Spiegel \& Burrows) planet cooling models, we rule out an HR 8799 f with mass of 5 $M_{J}$ (7 $M_{J}$), 7 $M_{J}$ (10 $M_{J}$), and 12 $M_{J}$ (13 $M_{J}$) at $r_{proj}$ $\sim$ 12 $AU$, 9 $AU$, and 5 $AU$, respectively. All four HR 8799 planets have red early T dwarf-like $L^\prime$ - [4.05] colors, suggesting that their SEDs peak in between the $L^\prime$ and $M^\prime$ broadband filters. We find no statistically significant difference in HR 8799 cde's colors. Atmosphere models assuming thick, patchy clouds appear to better match HR 8799 bcde's photometry than models assuming a uniform cloud layer. While non-equilibrium carbon chemistry is required to explain HR 8799 bc's photometry/spectra, evidence for it from HR 8799 de's photometry is weaker. Future, deep IR spectroscopy/spectrophotometry with the Gemini Planet Imager, SCExAO/CHARIS, and other facilities may clarify whether the planets are chemically similar or heterogeneous.

[11]  arXiv:1409.5136 [pdf, ps, other]
Title: Detailed modelling of a large sample of Herschel sources in the Lockman Hole: identification of cold dust and of lensing candidates through their anomalous SEDs
Authors: Michael Rowan-Robinson (Imperial College), Lingyu Wang (Durham University), Julie Wardlow (University of Copenhagen), Duncan Farrah (Virginia Tech), Seb Oliver (Sussex University), Jamie Bock (JPL), Charlotte Clarke (Caltech), David Clements (Imperial College), Edo Ibar (Universidad de Valparaiso), Eduardo Gonzalez-Solares (IoA Cambridge), Lucia Marchetti (Open University), Douglas Scott (University of British Columbia), Anthony Smith (Sussex University), Mattia Vaccari (University of Western Cape), Ivan Valtchanov (European Space Science Centre Madrid)
Comments: 18 pages, 46 figures, accepted for publication MNRAS. arXiv admin note: text overlap with arXiv:1006.0120
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We have studied in detail a sample of 967 SPIRE sources with 5-sigma detections at 350 and 500 micron and associations with Spitzer-SWIRE 24 micron galaxies in the HerMES-Lockman survey area, fitting their mid- and far-infrared, and submillimetre, SEDs in an automatic search with a set of six infrared templates. For almost 300 galaxies we have modelled their SEDs individually to ensure the physicality of the fits. We confirm the need for the new cool and cold cirrus templates, and also of the young starburst template, introduced in earlier work. We also identify 109 lensing candidates via their anomalous SEDs and provide a set of colour-redshift constraints which allow lensing candidates to be identified from combined Herschel and Spitzer data. The picture that emerges of the submillimetre galaxy population is complex, comprising ultraluminous and hyperluminous starbursts, lower luminosity galaxies dominated by interstellar dust emission, lensed galaxies and galaxies with surprisingly cold (10-13K) dust. 11 % of 500$\mu$m selected sources are lensing candidates. 70 % of the unlensed sources are ultraluminous infrared galaxies and 26 % are hyperluminous. 34 % are dominated by optically thin interstellar dust ('cirrus') emission, but most of these are due to cooler dust than is characteristic of our Galaxy. At the highest infrared luminosities we see SEDs dominated by M82, Arp220 and young starburst types, in roughly equal proportions.

[12]  arXiv:1409.5137 [pdf, ps, other]
Title: An Improved Determination of the Lithium Depletion Boundary Age of Blanco 1 and a First Look on the Effects of Magnetic Activity
Comments: 25 pages, 12 figures, 3 tables
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The Lithium Depletion Boundary (LDB) is a robust method for accurately determining the ages of young clusters, but most pre-main-sequence models used to derive LDB ages do not include the effects of magnetic activity on stellar properties. In light of this, we present results from our spectroscopic study of the very low-mass members of the southern open cluster Blanco~1 using the Gemini-North telescope, program IDs: GN-2009B-Q-53 and GN-2012B-Q-96. We obtained GMOS spectra at intermediate resolution for cluster candidate members with $I$$\approx$13--20 mag. From our sample of 43 spectra, we find 14 probable cluster members by considering proximity to the cluster sequence in an $I/I-K\rm_s$ color-magnitude diagram, agreement with the cluster's systemic radial velocity, and magnetic activity as a youth indicator. We systematically analyze the H$\alpha$ and Li features and update the LDB age of Blanco~1 to be $126^{+13}_{-14}$ Myr. Our new LDB age for Blanco 1 shows remarkable coevality with the benchmark Pleiades open cluster. Using available empirical activity corrections, we investigate the effects of magnetic activity on the LDB age of Blanco~1. Accounting for activity, we infer a corrected LDB age of $114^{+9}_{-10}$ Myr. This work demonstrates the importance of accounting for magnetic activity on LDB inferred stellar ages, suggesting the need to re-investigate previous LDB age determinations.

[13]  arXiv:1409.5148 [pdf, ps, other]
Title: The Turbulent Origin of Spin-Orbit Misalignment in Planetary Systems
Comments: 11 pages, 8 figures. Submitted to MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The turbulent environment from which stars form leads to misalignment between the stellar spin and the remnant protoplanetary disk. By using hydrodynamic and magnetohydrodynamic simulations, we demonstrate that a wide range of stellar obliquities are produced as a by-product of forming a star within a turbulent environment. We present a simple semi-analytic model that reveals this connection between the turbulent motions and the orientation of a star and its disk. Our results are consistent with the observed obliquity distribution of hot Jupiters. Migration of misaligned hot Jupiters may, therefore, be due to tidal dissipation in the disk, rather than tidal dissipation of the star-planet interaction.

[14]  arXiv:1409.5150 [pdf, ps, other]
Title: The Size of Star Clusters Accreted by the Milky Way
Comments: 7 pages, 6 figures, Accepted for publication MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We perform N-body simulations of a cluster that forms in a dwarf galaxy and is then accreted by the Milky Way to investigate how a cluster's structure is affected by a galaxy merger. We find that the cluster's half mass radius will respond quickly to this change in potential. When the cluster is placed on an orbit in the Milky Way with a stronger tidal field the cluster experiences a sharp decrease in size in response to increased tidal forces. Conversely, when placed on an orbit with a weaker tidal field the cluster expands since tidal forces decrease and stars moving outwards due to internal effects remain bound at further distances than before. In all cases, we find that the cluster's half mass radius will eventually be indistinguishable from a cluster that has always lived in the Milky Way on that orbit. These adjustments occur within 1-2 half mass relaxation times of the cluster in the dwarf galaxy. We also find this effect to be qualitatively independent of the time that the cluster is taken from the dwarf galaxy. In contrast to the half mass radius, we show the core radius of the cluster is not affected by the potential the cluster lives in. Our work suggests that structural properties of accreted clusters are not distinct from clusters born in the Milky Way. Other cluster properties, such as metallicity and horizontal branch morphology, may be the only way to identify accreted star clusters in the Milky Way.

[15]  arXiv:1409.5152 [pdf, ps, other]
Title: Two New Catalogues of Superclusters of Abell/ACO Galaxy Clusters out to redshift 0.15
Comments: 15 pages, 8 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present two new catalogues of superclusters of galaxies out to a redshit of z = 0.15, based on the Abell/ACO cluster redshift compilation maintained by one of us (HA). The first of these catalogues, the all-sky Main SuperCluster Catalogue (MSCC), is based on only the rich (A-) Abell clusters, and the second one, the Southern SuperCluster Catalogue (SSCC), covers declinations delta < -17 deg and includes the supplementary Abell S-clusters. A tunable Friends-of-Friends (FoF) algorithm was used to account for the cluster density decreasing with redshift and for different selection functions in distinct areas of the sky. We present the full list of Abell clusters used, together with their redshifts and supercluster memberships and including the isolated clusters. The SSCC contains about twice the number of superclusters than MSCC for delta < -17 deg, which we found to be due to: (1) new superclusters formed by A-clusters in their cores and surrounded by S-clusters (50%), (2) new superclusters formed by S-clusters only (40%), (3) redistribution of member clusters by fragmentation of rich (multiplicity m > 15) superclusters (8%), and (4) new superclusters formed by the connection of A-clusters through bridges of S-clusters (2%). Power-law fits to the cumulative supercluster multiplicity function yield slopes of alpha = -2.0 and alpha = -1.9 for MSCC and SSCC respectively. This power-law behavior is in agreement with the findings for other observational samples of superclusters, but not with that of catalogues based on cosmological simulations.

[16]  arXiv:1409.5153 [pdf, ps, other]
Title: Gravitational waves from the evolution of magnetic field after electroweak epoch
Comments: 21 pages, 1 figure
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

It was recently demonstrated that the evolution of helical magnetic field in the primordial plasma at temperatures $T\gtrsim10$ MeV is affected by the phenomenon of chiral quantum anomaly in the electroweak model, leading to a possibility of self-sustained existence of magnetic field and chiral asymmetry in the electronic distribution. This may serve as a mechanism for generating primordial magnetic field in the early universe. Violent magnetic-field generation may lead to production of gravitational waves which, regardless of the fate of magnetic field itself, survive until today. We estimate the threshold value of the initial chiral asymmetry above which the generated gravitational waves would affect the big-bang nucleosynthesis and would show up in the current and future experiments on gravitational-wave detection.

[17]  arXiv:1409.5160 [pdf, ps, other]
Title: Environmental Influences on the LIGO Gravitational Wave Detectors during the 6th Science Run
Comments: 18 pages
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We describe the influence of environmental noise on LIGO detectors in the sixth science run (S6), from July 2009 to October 2010. We show results from experimental investigations testing the coupling level and mechanisms for acoustic, electromagnetic/magnetic and seismic noise to the instruments. We argument the sensors' importance for vetoes of false positive detections, report estimates of the noise sources' contributions to the detector background, and discuss the ways in which environmental coupling should be reduced in the LIGO upgrade, Advanced LIGO.

[18]  arXiv:1409.5183 [pdf, ps, other]
Title: The Galaxy Cosmological Mass Function
Authors: Amanda R. Lopes (1), Alvaro Iribarrem (1), Marcelo B. Ribeiro (2), William R. Stoeger (3) ((1) Observatório do Valongo, Universidade Federal do Rio de Janeiro, (2) Instituto de Física, Universidade Federal do Rio de Janeiro, (3) Vatican Observatory Research Group, Steward Observatory, University of Arizona)
Comments: In memory of William R. Stoeger (1943-2014). LaTeX, 8 pages, 7 figures. To appear in "Astronomy and Astrophysics"
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

We study the galaxy cosmological mass function (GCMF) in a semi-empirical relativistic approach using observational data provided by galaxy redshift surveys. Starting from the theory of Ribeiro & Stoeger (2003, arXiv:astro-ph/0304094) between the mass-to-light ratio, the selection function obtained from the luminosity function (LF) data and the luminosity density, the average luminosity $L$ and the average galactic mass $\mathcal{M}_g$ are computed in terms of the redshift. $\mathcal{M}_g$ is also alternatively estimated by a method that uses the galaxy stellar mass function (GSMF). Comparison of these two forms of deriving the average galactic mass allows us to infer a possible bias introduced by the selection criteria of the survey. We used the FORS Deep Field galaxy survey sample of 5558 galaxies in the redshift range $0.5 < z < 5.0$ and its LF Schechter parameters in the B-band, as well as this sample's stellar mass-to-light ratio and its GSMF data. Assuming ${\mathcal{M}_{g_0}} \approx 10^{11} \mathcal{M}_\odot$ as the local value of the average galactic mass, the LF approach results in $L_{B} \propto (1+z)^{(2.40 \pm 0.03)}$ and $\mathcal{M}_g \propto (1+z)^{(1.1\pm0.2)}$. However, using the GSMF results produces $\mathcal{M}_g \propto (1+z)^{(-0.58 \pm 0.22)}$. We chose the latter result as it is less biased. We then obtained the theoretical quantities of interest, such as the differential number counts, to calculate the GCMF, which can be fitted by a Schechter function. The derived GCMF follows theoretical predictions in which the less massive objects form first, being followed later by more massive ones. In the range $0.5 < z < 2.0$ the GCMF has a strong variation that can be interpreted as a higher rate of galaxy mergers or as a strong evolution in the star formation history of these galaxies.

[19]  arXiv:1409.5197 [pdf, ps, other]
Title: A theoretical estimate of intrinsic ellipticity bispectra induced by angular momenta alignments
Authors: Philipp M. Merkel (ITA/ZAH, Heidelberg), Bjoern Malte Schaefer (ARI/ZAH, Heidelberg)
Comments: 12 pages, 6 figures, MNRAS accepted
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Intrinsically aligned galaxy shapes are one of the most important systematics in cosmic shear measurements. So far theoretical studies of intrinsic alignments almost exclusively focus on their statistics at the two-point level. Results from numerical simulations, however, suggest that third-order measures might be even stronger affected. We therefore investigate the (angular) bispectrum of intrinsic alignments. In our fully analytical study we describe intrinsic galaxy ellipticities by a physical alignment model, which makes use of tidal torque theory. We derive expressions for the various combinations of intrinsic and gravitationally induced ellipticities, i.e. III-, GII- and GGI-alignments, and compare our results to the shear bispectrum, the GGG-term. The latter is computed using hyper-extended perturbation theory. Considering equilateral and squeezed configurations we find that for a Euclid-like survey intrinsic alignments (III-alignments) start to dominate on angular scales smaller than 20 arcmin and 13 arcmin, respectively. This sensitivity to the configuration-space geometry may allow to exploit the cosmological information contained in both the intrinsic and gravitationally induced ellipticity field. On smallest scales (l ~ 3000) III-alignments exceed the lensing signal by at least one order of magnitude. The amplitude of the GGI-alignments is the weakest. It stays below that of the shear field on all angular scales irrespective of the wave-vector configuration.

[20]  arXiv:1409.5227 [pdf, ps, other]
Title: First analysis of eight Algol-type systems: V537 And, GS Boo, AM CrB, V1298 Her, EL Lyn, FW Per, RU Tri, and WW Tri
Authors: P. Zasche
Comments: 15 pages, 10 pages of online-only data tables. Published in New Astronomy, Volume 34, p. 253-261, 2015
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Analyzing available photometry from the Super WASP and other databases, we performed the very first light curve analysis of eight eclipsing binary systems V537 And, GS Boo, AM CrB, V1298 Her, EL Lyn, FW Per, RU Tri, and WW Tri. All of these systems were found to be detached ones of Algol-type, having the orbital periods of the order of days. 722 new times of minima for these binaries were derived and presented, trying to identify the period variations caused by the third bodies in these systems.

[21]  arXiv:1409.5228 [pdf, ps, other]
Title: The physical origin of the universal accretion history of dark matter halos
Comments: 21 pages, 19 figures, 3 tables. Submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Understanding the universal accretion history of dark matter halos is the first step towards determining the origin of their universal structure. In this work, we begin by using the extended Press-Schechter (EPS) formalism to show that the halo mass accretion history is determined by the growth rate of initial density perturbations, and that it follows the expression M(z)=M0(1+z)^{af(M0)}e^{-f(M0)z}, where M0=M(z=0), a depends on cosmology and f(M0) depends only on the matter power spectrum. We then explore the relation between the structure of the inner dark matter halo and halo mass history using a suite of cosmological, hydrodynamical simulations. We confirm that the formation time, defined as the time when the virial mass of the main progenitor equals the mass enclosed within the scale radius, correlates strongly with concentration. We provide a fitting formula for the relation between concentration and formation time, from which we show analytically that the scatter in formation time determines the scatter in concentration. Based on our analytic and numerical work, we conclude that the concentration is determined by the halo mass history, and show by simple modeling that one can be determined from the other. Since halo concentrations are characterized by their mass histories, and the latter are described by the initial density perturbations and the growth rate, we have therefore established the physical link between halo concentrations and the initial density perturbation field. Finally, we model the halo mass history as M(z)=M0(1+z)^{alpha}e^{beta z} and find a direct correlation between the parameters alpha, beta and concentration. We provide fitting formulas for the halo mass history and accretion rate as a function of halo mass, and demonstrate how halo mass history changes according to the adopted mass definition and cosmology.

[22]  arXiv:1409.5234 [pdf, ps, other]
Title: Characteristics of bright ab-type RR Lyrae stars from the ASAS and WASP surveys
Authors: Marek Skarka
Comments: 15 pages, 16 figures, 5 tables. Accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In this paper we present results based on high-density, high-precision WASP light curves supplemented with lower-precision photometry from ASAS for 268 RR Lyrae stars (176 regular, 92 Blazhko). Light curves were Fourier-decomposed, and coefficients from WASP were transformed to the ASAS standard using 24 common stars. Coefficients were then compared with similar data from Galactic globular clusters, the Galactic bulge, LMC, and SMC. Using Fourier coefficients we also calculated physical parameters via standard equations from the literature. We confirmed the results of previous authors, including lower amplitudes and longer rise times for Blazhko stars. It was found that in the $R_{21}$ vs. $R_{31}$ plot the location of a star depends mainly on its metallicity and that Blazhko stars prefer a different location than modulation-free stars. Field and globular-cluster RR Lyrae variables have a different $\phi_{21}$ and $\phi_{31}$ than stars in the LMC, SMC and in Galactic bulge. Although there are some weak indications that Blazhko stars could prefer a slightly lower metallicity and shorter periods, no convincing proof was found. The most interesting highlight is the identification of a very recently proposed new group of metal-rich RR Lyrae type stars. These low-luminous, metal-strong variables, which comprise both Blazhko and regular stars, have shorter periods and about a 180 K higher temperature at constant $(B-V)_{0}$ than the rest of the stars in the sample.

[23]  arXiv:1409.5247 [pdf, ps, other]
Title: A state-of-the-art analysis of the dwarf irregular galaxy NGC 6822
Comments: 9 pages, 11 figures, Accepted to A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a detailed photometric study of the dwarf irregular galaxy NGC 6822 aimed at investigating the properties of its stellar populations and, in particular, the presence of stellar radial gradients. Our goal is to analyse the stellar populations in six fields, which cover the whole bar of this dwarf galaxy. We derived the quantitative star formation history (SFH) of the six fields using the IAC method, involving IAC-pop/MinnIAC codes. The solutions we derived show an enhanced star formation rate (SFR) in Fields 1 and 3 during the past 500 Myr. The SFRs of the other fields are almost extinguished at very recent epochs and. We study the radial gradients of the SFR and consider the total mass converted into stars in two time intervals (between 0 and 0.5 Gyr ago and between 0.5 and 13.5 Gyr ago). We find that the scale lengths of the young and intermediate-to-old populations are perfectly compatible, with the exception of the young populations in Fields 1 and 3. The recent SF in these two fields is greater than in the other ones. This might be an indication that in these two fields we are sampling incipient spiral arms. Further evidence and new observations are required to prove this hypothesis. In addition, we derived the age-metallicity relations. As expected, the metallicity increases with time for all of the fields. We do not observe any radial gradient in the metallicity.

[24]  arXiv:1409.5258 [pdf, other]
Title: Time-series photometry of the O4 I(n)fp star zeta Puppis
Comments: MNRAS, in press
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We report a time-series analysis of the O4 I(n)fp star zeta Pup, based on optical photometry obtained with the SMEI instrument on the Coriolis satellite, 2003--2006. A single astrophysical signal is found, with P = (1.780938 \pm 0.000093) d and a mean semi-amplitude of (6.9 \pm 0.3) mmag. There is no evidence for persistent coherent signals with semi-amplitudes in excess of ca. 2~mmag on any of the timescales previously reported in the literature. In particular, there is no evidence for a signature of the proposed rotation period, ca. 5.1~days; zeta Pup is therefore probably not an oblique magnetic rotator. The 1.8-day signal varies in amplitude by a factor ca. 2 on timescales of 10--100d (and probably by more on longer timescales), and exhibits modest excursions in phase, but there is no evidence for systematic changes in period over the 1000-d span of our observations. Rotational modulation and stellar-wind variability appear to be unlikely candidates for the underlying mechanism; we suggest that the physical origin of the signal may be pulsation associated with low-l oscillatory convection modes.

[25]  arXiv:1409.5261 [pdf, ps, other]
Title: Photosphere emission in the X-Ray Flares of Swift Gamma-Ray Bursts and Implications for the Fireball Properties
Comments: 31 pages, 8 figures, and 4 tables. Accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

X-ray flares of gamma-ray bursts (GRBs) are usually observed in the soft X-ray range and the spectral coverage is limited. In this paper, we present an analysis of 32 GRB X-ray flares that are simultaneously observed by both BAT and XRT on board the Swift mission, so a joint spectral analysis with a wider spectral coverage is possible. Our results show that the joint spectra of 19 flares are fitted with the absorbed single power-law or the Band function models. More interestingly, the joint spectra of the other 13 X-ray flares are fitted with the absorbed single power-law model plus a black body (BB) component. Phenomenally, the observed spectra of these 13 flares are analogous to several GRBs with a thermal component, but only with a much lower temperature of $kT=1\sim 3$ keV. Assuming that the thermal emission is the photosphere emission of the GRB fireball, we derive the fireball properties of the 13 flares that have redshift measurements, such as the bulk Lorentz factor $\Gamma_{\rm ph}$ of the outflow. The derived $\Gamma_{\rm ph}$ range from $50$ to $150$ and a relation of $\Gamma_{\rm ph}$ to the thermal emission luminosity is found. It is consistent with the $\Gamma_0-L_{\rm iso}$ relation that are derived for the prompt gamma-ray emission. We discuss the physical implications of these results within the content of jet composition and radiation mechanism of GRBs and X-ray flares.

[26]  arXiv:1409.5266 [pdf]
Title: Instrumentation for the detection and characterization of exoplanets
Comments: Review article for Nature Insight on exoplanets. (Published version available at: this http URL)
Journal-ref: Nature 513, 358-366 (2014)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

In no other field of astrophysics has the impact of new instrumentation been as substantial as in the domain of exoplanets. Before 1995 our knowledge about exoplanets was mainly based on philosophical and theoretical considerations. The following years have been marked, instead, by surprising discoveries made possible by high-precision instruments. More recently the availability of new techniques moved the focus from detection to the characterization of exoplanets. Next-generation facilities will produce even more complementary data that will lead to a comprehensive view of exoplanet characteristics and, by comparison with theoretical models, to a better understanding of planet formation.

[27]  arXiv:1409.5268 [pdf, other]
Title: On the diversity of magnetic interactions in close-in star-planet systems
Comments: 18 pages, 11 figures, 4 tables, accepted for publication in The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Magnetic interactions between close-in planets and their host star can play an important role in the secular orbital evolution of the planets, as well as the rotational evolution of their host. As long as the planet orbits inside the Alfv\'en surface of the stellar wind, the magnetic interaction between the star and the planet can modify the wind properties and also lead to direct angular momentum transfers between the two. We model these star-planet interactions using compressible magneto-hydrodynamic (MHD) simulations, and quantify the angular momentum transfers between the star, the planet, and the stellar wind. We study the cases of magnetized and non-magnetized planets and vary the orbital radius inside the Alfv\'en surface of the stellar wind. Based on a grid of numerical simulations, we propose general scaling laws for the modification of the stellar wind torque, for the torque between the star and the planet, and for the planet migration associated with the star-planet magnetic interactions. We show that when the coronal magnetic field is large enough and the star is rotating sufficiently slowly, the effect of the magnetic star-planet interaction is comparable to tidal effects and can lead to a rapid orbital decay.

[28]  arXiv:1409.5300 [pdf, ps, other]
Title: Foreground removal for SKA EoR with the Correlated Component Analysis
Comments: 12 pages, 15 figures, submitted to MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We apply the Correlated Component Analysis (CCA) method on simulated data of the Square Kilometre Array, with the aim of accurately cleaning the 21 cm reionization signal from diffuse foreground contamination. The CCA has been developed for the Cosmic Microwave Background, but the application of the Fourier-domain implementation of this method to the reionization signal is straightforward.
The CCA is a parametric method to estimate the frequency behaviour of the foregrounds from the data by using second-order statistics. We test its performance on foreground simulations of increasing complexity, designed to challenge the parametric models adopted. We also drop the assumption of spectral smoothness that most of the methods rely upon. We are able to clean effectively the simulated data across the explored frequency range (100-200 MHz) for all the foreground simulations. This shows that the CCA method is very promising for EoR component separation.

[29]  arXiv:1409.5336 [pdf, ps, other]
Title: New Analysis Indicates No Thermal Inversion in the Atmosphere of HD 209458b
Comments: 8 pages, 5 figures; accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

An important focus of exoplanet research is the determination of the atmospheric temperature structure of strongly irradiated gas giant planets, or hot Jupiters. HD 209458b is the prototypical exoplanet for atmospheric thermal inversions, but this assertion does not take into account recently obtained data or newer data reduction techniques. We re-examine this claim by investigating all publicly available Spitzer Space Telescope secondary-eclipse photometric data of HD 209458b and performing a self-consistent analysis. We employ data reduction techniques that minimize stellar centroid variations, apply sophisticated models to known Spitzer systematics, and account for time-correlated noise in the data. We derive new secondary-eclipse depths of 0.119 +/- 0.007%, 0.123 +/- 0.006%, 0.134 +/- 0.035%, and 0.215 +/- 0.008% in the 3.6, 4.5, 5.8, and 8.0 micron bandpasses, respectively. We feed these results into a Bayesian atmospheric retrieval analysis and determine that it is unnecessary to invoke a thermal inversion to explain our secondary-eclipse depths. The data are well-fitted by a temperature model that decreases monotonically between pressure levels of 1 and 0.01 bars. We conclude that there is no evidence for a thermal inversion in the atmosphere of HD 209458b.

[30]  arXiv:1409.5339 [pdf, other]
Title: HIP 3678: a hierarchical triple stellar system in the centre of the planetary nebula NGC 246
Authors: C. Adam, M. Mugrauer
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We report the detection of a new low-mass stellar companion to the white dwarf HIP 3678 A, the central star of the planetary nebula NGC 246. The newly found companion is located about 1 arcsec (at projected separation of about 500 au) north-east of HIP 3678 A, and shares a common proper motion with the white dwarf and its known comoving companion HIP 3678 B. The hypothesis that the newly detected companion is a non-moving background object can be rejected on a significance level of more than 8 $\sigma$, by combining astrometric measurements from the literature with follow-up astrometry, obtained with Wild Field Planetary Camera 2/\textit{Hubble Space Telescope} and NACO/Very Large Telescope. From our deep NACO imaging data, we can rule out additional stellar companions of the white dwarf with projected separations between 130 up to 5500 au. In the deepest high-contrast NACO observation, we achieve a detection limit in the \textit{Ks} band of about 20 mag, which allows the detection of brown dwarf companions with masses down to 36$\,\rmn{M_{jup}}$ at an assumed age of the system of 260 Myr. To approximate the masses of the companions HIP 3678 B and C, we use the evolutionary Baraffe et al. models and obtain about 0.85\,M$_{\sun}$ for HIP 3678 B and about 0.1 M$_{\sun}$ for HIP 3678 C. According to the derived absolute photometry, HIP 3678 B should be a early to mid-K dwarf (K2--K5), while HIP 3678 C should be a mid-M dwarf with a spectral type in the range between M5 and M6.

[31]  arXiv:1409.5357 [pdf, ps, other]
Title: X-ray emission from an FU Ori star in early outburst: HBC 722
Comments: to appear in Astronomy & Astrophysics Letters
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Aims: We conducted the first X-ray observations of the newly erupting FU~Ori-type outburst in HBC~722 (V2493 Cyg) with the aim to characterize its X-ray behavior and near-stellar environment during early outburst. Methods: We used data from the \XMM\ and \CXO\ X-ray observatories to measure X-ray source temperatures and luminosities as well as the gas column densities along the line of sight toward the source. Results: We report a \CXO\ X-ray detection of HBC~722 with an X-ray luminosity of $L_{\rm X}\approx 4\times 10^{30}~\mathrm{ergs~s}^{-1}$. The gas column density exceeds values expected from optical extinction and standard gas-to-dust ratios. We conclude that dust-free gas masses are present around the star, such as strong winds launched from the inner disk, or massive accretion columns. A tentative detection obtained by \XMM\ two years earlier after an initial optical peak revealed a fainter X-ray source with only weak absorption.

[32]  arXiv:1409.5389 [pdf]
Title: Theoretical Estimates of Integrated Sachs-Wolfe Effect Detection through EMU-ASKAP Survey with Confusion, Position Uncertainty, Shot Noise and SNR analysis
Comments: 23 pages,12 figures, Published in Just-in Issue of Canadian Journal of Physics on 10 September 2014
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The paper discusses ISW estimates through EMU-ASKAP survey.
The main ideas this paper covers include:
1- Discussion on source distribution, confusion, position accuracy and shotnoise (with discussion focusing on SN ratios).
2- Selection of maximum redshift and maximum 'l' ranges in relation with SN ratios.
Note: Complete abstract is available in the document.

[33]  arXiv:1409.5395 [pdf, ps, other]
Title: Time variability of the $γ$-ray binary HESS J0632+057
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We study changes in the $\gamma$--ray intensity at very high energies observed from the $\gamma$--ray binary HESS J0632+057. Publicly available data collected by Cherenkov telescopes were examined by means of a simple method utilizing solely the number of source and background events. Our results point to time variability in signal from the selected object consistent with periodic modulation of the source intensity.

[34]  arXiv:1409.5398 [pdf, ps, other]
Title: On the prospects of Near Earth Asteroid orbit triangulation using the Gaia satellite and Earth-based observations
Comments: Article accepted for publication in the proceedings of the International Symposium on Orbit Propagation and Determination held in Lille, France, 2011, to be published in 2014
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

Accurate measurements of osculating orbital elements are essential in order to understand and model the complex dynamic behavior of Near Earth Asteroids (NEAs). ESA's Gaia mission promises to have great potential in this respect. In this article we investigate the prospects of constraining orbits of newly discovered and known NEAs using nearly simultaneous observations from the Earth and Gaia. We find that observations performed simultaneously from two sites can effectively constrain preliminary orbits derived via statistical ranging. By linking discoveries stored in the Minor Planet Center databases to Gaia astrometric alerts one can identify nearly simultaneous observations of Near Earth Objects and benefit from improved initial orbit solutions at no additional observational cost.

[35]  arXiv:1409.5406 [pdf, other]
Title: The HI Chronicles of LITTLE THINGS BCDs II: The Origin of IC 10's HI Structure
Comments: 36 pages, 17 figures, accepted for publication in The Astronomical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA)

In this paper we analyze Very Large Array (VLA) telescope and Green Bank Telescope (GBT) atomic hydrogen (HI) data for the LITTLE THINGS(1) blue compact dwarf galaxy IC 10. The VLA data allow us to study the detailed HI kinematics and morphology of IC 10 at high resolution while the GBT data allow us to search the surrounding area at high sensitivity for tenuous HI. IC 10's HI appears highly disturbed in both the VLA and GBT HI maps with a kinematically distinct northern HI extension, a kinematically distinct southern plume, and several spurs in the VLA data that do not follow the general kinematics of the main disk. We discuss three possible origins of its HI structure and kinematics in detail: a current interaction with a nearby companion, an advanced merger, and accretion of intergalactic medium. We find that IC 10 is most likely an advanced merger or a galaxy undergoing accretion.
1:Local Irregulars That Trace Luminosity Extremes, The HI Nearby Galaxy Survey; https://science.nrao.edu/science/surveys/littlethings

[36]  arXiv:1409.5409 [pdf, ps, other]
Title: Fractal analysis of the galaxy distribution in the redshift range 0.45 < z < 5.0
Authors: G. Conde-Saavedra (1), A. Iribarrem (1), Marcelo B. Ribeiro (2) ((1) Observatório do Valongo, Universidade Federal do Rio de Janeiro, (2) Instituto de Física, Universidade Federal do Rio de Janeiro)
Comments: LaTex, 15 pages, 28 figures, 4 tables. To appear in "Physica A"
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

Evidence is presented that the galaxy distribution can be described as a fractal system in the redshift range of the FDF galaxy survey. The fractal dimension $D$ was derived using the FDF galaxy volume number densities in the spatially homogeneous standard cosmological model with $\Omega_{m_0}=0.3$, $\Omega_{\Lambda_0}=0.7$ and $H_0=70 \; \mbox{km} \; {\mbox{s}}^{-1} \; {\mbox{Mpc}}^{-1}$. The ratio between the differential and integral number densities $\gamma$ and $\gamma^\ast$ obtained from the red and blue FDF galaxies provides a direct method to estimate $D$, implying that $\gamma$ and $\gamma^\ast$ vary as power-laws with the cosmological distances. The luminosity distance $d_{\scriptscriptstyle L}$, galaxy area distance $d_{\scriptscriptstyle G}$ and redshift distance $d_z$ were plotted against their respective number densities to calculate $D$ by linear fitting. It was found that the FDF galaxy distribution is characterized by two single fractal dimensions at successive distance ranges. Two straight lines were fitted to the data, whose slopes change at $z \approx 1.3$ or $z \approx 1.9$ depending on the chosen cosmological distance. The average fractal dimension calculated using $\gamma^\ast$ changes from $\langle D \rangle=1.4^{\scriptscriptstyle +0.7}_{\scriptscriptstyle -0.6}$ to $\langle D \rangle=0.5^{\scriptscriptstyle +1.2}_{\scriptscriptstyle -0.4}$ for all galaxies, and $D$ decreases as $z$ increases. Small values of $D$ at high $z$ mean that in the past galaxies were distributed much more sparsely and the large-scale galaxy structure was then possibly dominated by voids. Results of Iribarrem et al. (2014, arXiv:1401.6572) indicating similar fractal features with $\langle D \rangle =0.6 \pm 0.1$ in the far-infrared sources of the Herschel/PACS evolutionary probe (PEP) at $1.5 \lesssim z \lesssim 3.2$ are also mentioned.

[37]  arXiv:1409.5413 [pdf, other]
Title: An in situ measurement of the radio-frequency attenuation in ice at Summit Station, Greenland
Comments: 7 pages, 7 figures, submitted to Journal of Glaciology
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Experiment (hep-ex)

We report an in situ measurement of the electric field attenuation length at radio frequencies for the bulk ice at Summit Station, Greenland, made by broadcasting radio-frequency signals vertically through the ice and measuring the relative power in the return ground bounce signal. We find the depth-averaged field attenuation length to be 947 +92/-85 meters at 75 MHz. While this measurement has clear radioglaciological applications, the radio clarity of the ice also has implications for the detection of ultra-high energy (UHE) astrophysical particles via their radio emission in dielectric media such as ice. The measured attenuation length at Summit Station is comparable to previously measured radio-frequency attenuation lengths at candidate particle detector sites around the world, and strengthens the case for Summit Station as the most promising northern site for UHE neutrino detection.

[38]  arXiv:1409.5416 [pdf, ps, other]
Title: Crowded-field image simulator for WSO-UV/ISSIS: first functional version developed by the Glendama team
Comments: 5 pages, 4 figures, accepted for publication in ApSS (Special Issue UV Astronomy 3). The Crowded-field Image Simulator (CIS) for ISSIS is freely available at this http URL (see also this http URL for simulations of gravitationally lensed AGN)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We are developing a web-based interactive software to simulate crowded-field imaging with the Imaging and Slitless Spectrograph Instrument for Surveys (ISSIS) on board the future World Space Observatory - Ultraviolet (WSO-UV). This new tool is aimed to prepare WSO-UV/ISSIS proposals to observe multicomponent targets and dense fields. For a given combination of UV channel, filters and exposure time, the user creates a set of point-like and extended sources (source model). This source model produces a final image, which takes into account a pixelated field of view, a realistic conversion between physical flux and counts per second, the convolution with the expected point spread function, a sky background and noise fluctuations. The current version of the simulator is available at the Gravitational LENses and DArk MAtter (Glendama) website, and it allows users to specify all relevant parameters of each point-like or extended source, drag-and-drop sources by using a mouse or a fingertip/stylus on a touchscreen, change the frame size or the brightness scale, etc.

[39]  arXiv:1409.5428 [pdf, ps, other]
Title: Connecting the interstellar magnetic field at the heliosphere to the Loop I superbubble
Comments: To be published in the proceedings of the 13th Annual International Astrophysics Conference: "Voyager, IBEX, and the Interstellar Medium"
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The local interstellar magnetic field affects both the heliosphere and the surrounding cluster of interstellar clouds (CLIC). Measurements of linearly polarized starlight provide the only test of the magnetic field threading the CLIC. Polarization measurements of the CLIC magnetic field show multiple local magnetic structures, one of which is aligned with the magnetic field traced by the center of the "ribbon" of energetic neutral atoms discovered by the Interstellar Boundary Explorer (IBEX). Comparisons between the bulk motion of the CLIC through the local standard of rest, the magnetic field direction, the geometric center of Loop I, and the polarized dust bridge extending from the heliosphere toward the North Polar Spur direction all suggest that the CLIC is part of the rim region of the Loop I superbubble.