1811.00605
The nature of fast radio bursts
Pen
Physical constraints on the sources of fast radio bursts are few, and therefore viable theoretical models are many. However, no one model can match all the available observational characteristics, meaning that these radio bursts remain one of the most mysterious phenomena in astrophysics.
1811.00637
Constraining the mass density of free-floating black holes using razor-thin lensing arcs
Banik, van den Bosch, et al
SL of AGNs in the radio can result in razor-thin arcs, with a thickness of less than a milli-arcsecond, if observed at the resolution achievable with very-long baseline interferometry (VLBI). Such razor-thin arcs provide a unique window on the coarseness of the matter distribution between source and observer. In this paper, investigate to what extent such razor-thin arcs can constrain the number density and mass function of 'free-floating' black holes, defined as black holes that do not, or no longer, reside at the center of a galaxy. These can be either primordial in origin or arise as by-products of the evolution of super-massive black holes in galactic nuclei. When sufficiently close to the line-of-siight, free-floating BHs cause kink-like distortions in the arcs, which are detectable by eye in the VLBI images as longs the BH mass exceeds ~1000 Msun. Using a crude estimate for the detectability of such distortions, analytically compute constraints on the matter density of free-floating BHs resulting from null-detections of distortions along a realistic, fiducial arc, and find them to be comparable to those from quasar milli-lensing. Also use predictions from a large hydrodynamical simulation for the demographics of free-floating BHs that are not primordial in origin, and show that their predicted mass density is roughly four orders of magnitude below the constraints achievable with a single razor-thin arc.
1811.01139
Weak lensing reveals a tight connection between dark matter halo mass and the distribution of stellar mass in massive galaxies
Huang, Leauthaud, Hearin, Behroozi, et al
Using deep images from HSC survey and taking advantage of its unprecedented weak lensing capabilities, reveal a remarkably tight connection between the stellar mass distribution of massive central galaxies and their host dark matter halo mass. Massive galaxies with more extended stellar mass distributions tend to live in more massive dark matter haloes. Explain this connection with a phenomenological model that assumes, (1) a tight relation between the halo mass and the total stellar content in the halo, (2) that the fraction of in-situ and ex-situ mass at r<10 kpc depends on halo mass. This model provides an excellent description of the SMF of total stellar mass M_star^Max and stellar mass within inner 10 kpc (Mstar^10) and also reproduces the HSC WL signals of massive galaxies with different stellar mass distributions. The best-fit model shows that halo mass varies significantly at fixed total stellar mass (as much as 0.4 dex) with a clear dependence on M_star^10. The two-parameter Mstar^Max - MStar^10 description provides a more accurate picture of the galaxy-halo connection at the high-mass end than the simple stellar-halo mass relation (SHMR) and opens a new window to connect the assembly history of haloes with those of central galaxies. The model also predicts that the ex-situ component dominates the mass profiles of galaxies at r<10 kpc for log Mstar >= 11.7. The code used for this paper is available online: https://github.com/dr-guangtou/asap.
1811.01679
Magnifications of paired micro-images emerging from a micro-lensing critical curve: breakdown of the inverse square root approximation
Weisenbach, Schlechter, Wambsganss
Studies of the inner regions of micro-lensed AGN during caustic crossing events have often relied upon the approximation that the magnification near a fold caustic is inversely proportional to the square root of the source-caustic distance. Examine here the behavior of the magnifications of individual micro-images, specifically micro-minima, for a point source near fold caustics. Find that there are often already noticeable deviations between actual magnifications and approximation at distances (rendered dimensionless by the 'flux factor', or caustic strength) of 0.1. Present some statistics on the behavior of the magnifications of the micro-minima examined. Additionally, provide statistics on values of the caustic strength for images C and D of WSO 2237+0305. Finally, suggest an alternative approximation for the magnification near fold caustics and show how it alters the magnification profile of a uniform disc from that of the standard approximation.
1811.01809
Brightest cluster galaxy alignments in merging clusters
Wittman, Foote, Golovich
The orientations of brightest cluster galaxies (BCGs) and their host clusters then to be aligned, but the mechanism driving this is not clear. To probe the role of cluster mergers in this process, quantify alignments of BCGs in clusters undergoing major mergers (up to ~1 Gyr after first pericenter). Find alignments entirely consistent with those of clusters in general. This suggests that alignments are robust against major cluster mergers. If, conversely, major mergers actually help orient the BCG, such a process is acting quickly because the orientation is in place within ~1 Gyr after fist pericenter.
1811.01962
Revisiting the size-luminosity relation the era of ultra diffuse galaxies
Danieli, van Dokkum
Galaxies are generally found to follow a relation between their size and luminosity, such that luminous galaxies typically have large sizes. The recent identification of a significant population of galaxies with large sizes but low luminosities ('ultra diffuse galaxies', or UDGs) raises the question whether the inverse is also true, thetas, whether large galaxies typically have high luminosities. Here, address this question by studying a size-limited sample of galaxies in the Coma cluster. Sleect red cluster galaxies with sizes r_eff>2kpc down to M_g~-13 mag in an area of 9 deg^2, using carefully-filtered CHFT images. The sample is complete to a central surface brightness of mu_g,0 ~ 25.0 mag arcsec^{-2} and includes 90% of Dragonfly-discovered UDGs brighter than this limit. Unexpectedly, find that red, large galaxies have a fairly uniform distribution in the size-luminosity plane: there is no peak at the absolute magnitude implied by the canonical size-luminosity relation. The number of galaxies within ±0.5 magnitudes of the canonical peak (M_g=-19.69 for 2<r_eff<3 kpc) is a factor of ~9 smaller than the number of fainter galaxies with -19<M_g<-13. Large, faint galaxies such as UDGs are far more common than large galaxies that are on the size-luminosity relation. An implication is that, for large galaxies, size is not an indicator of halo mass. Finally, show that the structure of faint large galaxies is different from that of bright large galaxies: at fixed large size, the Sersic index decreases with magnitude following the relation log10 n ~ -0.067 M_g - 0.989.
1811.02368
The PAU Survey: Operation and orchestration of multi-band survey data
Tonello, et al
The Physics of the Accelerating Universe (PAU) Survey is an international project for the study of cosmological parameters associated with Dark Energy. PAU's 18-CCD camera (PAUCam), installed at the prime focus on the Willam Herschel Telescope at the Roque de los Muchachos Observatory (La Palma, canary Islands), scans parts of the northern sky, to collect low resolution spectral information of millions of galaxies with its unique set of 40 narrow-band filters in the optical range from 450 nm to 850 nm, and a set of 6 standard board band filters. The PAU data management (PAUdm) team is in charge of treating the data, including at a transfer from the observatory to the PAU Survey data center, hosted at Port d'Informació Clientífica (PIC). PAUdm is also in charge of the storage, data reduction and, finally, of making the results available to the scientific community. Describe the technical solutions adopted to cover different aspects of the PAU Survey data management, from the computing infrastructure to support the operations, to the software tools and web services for the data process orchestration and exploration. In particular, focus on the PAU database, developed for the coordination of the different PAUdm tasks, and to preserve and guarantee the consistence of data and metadata.
1811.02374
First cosmology results using Type Ia Spernovae from the Dark Energy Survey: Constraints on cosmological parameters
Abbott, et al
Present the first cosmological parameter constraints using measurements of SNe Ia from DES Supernova Program (DES-SN). The analysis uses a subsample of 207 spectroscopically confirmed SNe Ia from the first 3 years of DES-SN, combined with a low-redshift same of 122 SNe from the literature. The "DES-SN3YR" result from these 329 SNe Ia is based on a series of companion analyses covering SN Ia discovery, spectroscopic selection, photometry, calibration, distance bias corrections, and evaluation of systematic uncertainties. For a flat LCDM model, find a matter density Omega_m=0.331±0.038. For a flat wCDM model, and combining the SNIa constraints with those form the CMB, find a dark energy equation of state w=-0.978±0.059, and Omega_m=0.321±0.018. Fo a flat w0waCDM model, and combining probes from SN Ia, CMB and BAO, find w0=-0.885±0.114 and wa=0.387±0.430. These results are in agreement with a cosmological constant and with previous constraints using SNe Ia (Pantheon, JLA).
1811.02375
Cosmological constraints from multiple probes in the Dark Energy Survey
DES collaboration, et al
The combination of multiple observational probes has long been advocated as a powerful way to constrain cosmological parameters, in particular DE. DES has measured 207 spectroscopically-confirmed Type Ia SN lighcurves; the BAO feature; WL; and galaxy clustering. Present combined results from these probes, deriving constraints on the equation of state, w, of DE and its energy density in the Universe. Independently of other experiments, such as those that measure the CMB, the probes from this single photometric survey rule out a Universe with no dark energy, finding w=-0.80+0.09-0.11. The geometry is shown to be consistent with a spatially flat Universe, and report a constrain on the baryon density of Omega_b=0.069+0.009-0.012 that is independent of early Universe measurements. These results demonstrate the potential power of large multi-probe photometric surveys and pave the way for order of magnitude advances in the constraints on properties of DE and cosmology over the next decade.
1811.02376
First cosmological results using Type Ia Supernovae from the Dark Energy Survey: measurement of the Hubble Constant
Macaulay, et al
Present an improved measurement of H0 using the 'inverse distance ladder' method, which adds the information from 207 SNe Ia from DES at 0.018<z<0.85 to existing distance measurements of 122 low-z (<0.07) SNe Ia (Low-z) and measurements of BAOs. Whereas traditional measurements of H0 with SNe Ia use a distance ladder of parallax and Cepheid variable stars, the inverse distance ladder relies on absolute distance measurements from the BAOs to calibrate the intrinsic magnitude of the SNe Ia. Find H0=67.77±.13 km/s/Mpc (statistics and systematic uncertainties, 68% confidence). The measurement makes minimal assumptions about the underlying cosmological model, and the analysis was blinded to reduce confirmation bias. Examine possible systematic uncertainties and all are presently below the statistical uncertainties. The H0 value is consistent with estimate derived from CMB assuming a LCDM universe (Planck+2018).
1811.02518
Luminous red galaxies in the Kilo Degree Survey: Selection with broad-band photometry and weak lensing measurements
Vakili, et al
Use the overlap between multi band photometry of the KiDS and spectroscopic data based on SDSS and GAMA to infer the color-magnitude relation of red-sequence galaxies. Use this inferred relation to select LRGs in the range 0.1<z<0.7 over the entire KiDS DR3 footprint. Construct two samples of galaxies with different constant comoving densities and different luminosity thresholds. The selected red galaxies have photometric redshifts with typical photo-z errors of sigma_z~0.014 (1+z) that are nearly uniform with respect to observational systematics. This makes them an ideal set of galaxies for lensing and clustering studies. As an example, use the KiDS-450 cosmic shear catalogue to measure the mean tangential shear signal around the selected LERGs. Detect a significant WL signal for lenses out to z~0.7.
1811.02862
Atlas of cosmic ray-induced astrochemistry
Albertsson, Kaufmann, Menten
Cosmic-rays are the primary initiators of interstellar chemistry, and getting a better understanding of the varying impact they have on the chemistry of interstellar clouds throughout the MW will not only expand the understanding of interstellar medium chemistry in our own galaxy, but also aid in extra-galactic studies. This work uses the ALCHEMIC astrochemical modeling code to perform numerical simulations of chemistry for a range of ionization rates. Study the impact of variations in the cosmic ray ionization rate on molecular abundances under idealized conditions, given by constant temperatures and a fixed density of 1e4 cm^{-3}. As part of this study, examine whether observations of molecular abundances can be used to infer the cosmic ray ionization rate in such a simplified case. Find that intense cosmic-ray ionization results in molecules, in particular the large and complex ones, being largely dissociated, and the medium becoming increasingly atomic. Individual species have limitations in their use as probes of the cosmic ray ionization rate. At early time (<1 Myrs) ions such as N2H+ and HOC+ make the best probes, while at later times, neutral species such as HNCO and SO stand out, in particular due to their large abundance variations. It is however by combining species into pairs that the best probes are found. Molecular ions such as N2H+ combined with different neutral species can provide probe candidates that outmatch individual species, in particular N2H+/C4H, N2H+/C2H, HOC+/O and HOC+/HNCO. These still have limitations to their functional range, but are more functional as probes than individual species previously used.
1811.02976
Failures of Halofit model for computation of Fisher matrices
Reimberg, Bernaudeau, Nishimichi, Rizzato
Use a simple cosmo model with two parameters (A_s, n_s) to illustrate the impact of using Halofit on error forecast based on Fisher information matrix for a h^{-3} Gpc^3 volume survey. Show that Halofit fails to reproduce well the derivatives of the power spectrum with respect to the cosmo parameters despite the good fit produced for its amplitude. Argue that the poor performance on the derivatives prediction is a general feature of this model and exhibit the response function for th Halofit to show how it compares with the same quantity measured on simulations. The analytic structure of the Halofit response function points towards the origin of its weak performance at reproducing the derivatives of the non-linear power spectrum, which translate into unreliable Fisher information matrices.
1811.03095
Constraints on the existence of dark matter haloes by the M81 group and the Hickson compact groups of galaxies
Oehm, Kroupa
According to the standard model of cosmology the visible, baryonic matter of galaxies is embedded in DM haloes, thus extending the mass and the size of galaxies by one or two orders of magnitude. Taking into account dynamical friction between the DM haloes, the nearby located M81 group of galaxies as well as the Hickson compact groups of galaxies are here investigated with regard to their dynamical behavior. The results of the employment of the Markov Chain Monte Carlo method and the genetic algorithm show statistically substantial merger rates between galaxies, and long living constellations without merging galaxies comprise - apart from very few instances - initially unbound systems only. This results is derived based on three- and four-body calculations for model of rigid Navaroo-Frenk-White profiles for the DM haloes, but verified by the comparison to randomly chosen individual solutions for the M81 galaxy group with high-resolution simulations of live self-consistent systems (N-body calculations). In consequence, the observed compact confirmations of major galaxies are a very unlikely occurrence if DM haloes exist.
1811.03624
Inferences of $H_0$ in presence of a non-standard recombination
Chiang, Slosar
Measurements of the Hubble parameter from the distance ladder are in tension with indirect measurements based on the CMB data and the inverse distance ladder measurements at 3-4 sigma level. Consider phenomenological modification to the timing and width of the recombination process and show that they can significantly affect this tension. This possibility is appealing, because such modification affects both the distance to the last scattering surface and the calibration of the BAO ruler. Moreover, because only a very small fraction of the most energetic photons keep the early universe in the plasma state, it is possible that such modification could occur without affecting the energy density budget of the universe or being incompatible with the era tight limits on the departure from the black-body spectrum of CMB. In particular, find that under this simplified model, with a conservative subset of Planck data alone, H0=73.44-6.77+5.50 km/s/Mpc and in combination with BAO data H0=68.86-1.35+1.31 km/s/Mpc, decreasing the tension to ~2 sigma level. However, when combined with Planck lensing reconstruction and high-ell polarization data, the tension climbs back to ~2.7 sigma, despite the uncertainty on non-ladder H0 measurement more than doubling.
1811.03625
Observational determination of the galaxy bias from cosmic variance with a random pointing survey: clustering of z~2 galaxies from Hubble's BoRG survey
Cameron, Trenti, Livermore, van der Velden
Gravitational clustering broadens the count-in-cells distribution of galaxies for surveys along uncorrelated (well-separated) lines of sight beyond Poisson noise. A number of methods have proposed to measure this excess "cosmic" variance to constrain the galaxy bias (i.e. the strength of clustering) independently of the 2pt correlation function. Here, present an observational application of these methods using data from 141 uncorrelated fields (~700 arcmin^2 total) from Hubble's Brightest of Reionizing Galaxies (BoRG) survey. Use BoRG's broad-band imaging in optical and near infrared to identify N~1000 photometric candidates at z~2 through a combination of color selection and photometric z determination, building a magnitude-limited sample with m_AB<=24.5 in F160W. Detect a clear excess in the variance of the galaxy number counts distribution compared to Poisson expectations, from which galaxy bias b~3.63±0.57 is estimated. When divided by SED-fit classification into ~400 early-type and ~600 late-type candidates, estimate biases of b_early~4.06±0.67 and b_late~2.98±0.98 respectively. These estimates are consistent with previous measurements of the bias from the 2pt correlation function, and demonstrate that with N>~100 sight-lines, each containing N>~5 objects, the count-in-cell analysis provides a robust measurement of the bias. This implies that the method can be applied effectively to determine clustering properties (and characteristic dark-matter halo masses) of z~6-9 galaxies from a pure-parallel JWST survey similar in design to Hubble's BoRG survey.
1811.03631
The Spur and the Gap in GD-1: Dynamical evidence for a dark substructure in the Milky Way halo
Bonaca, Hogg, Price-Whelan, Conroy
Present a model for they interaction of the GD-1 stellar stream with a massive perturber that naturally explains many of the observed stream features, including a gap and an off-stream spur of stars. The model involves an impulse by a fast encounter, after which the stream grows a loop of stars at different orbital energies. At specific viewing angles, this loop appears offset from the stream track. The configuration-space observations are sensitive to the mass, age, impact parameter, and total velocity of the encounter, and future velocity observations will constrain the full velocity vector of the perturber. A quantitative comparison of the spur and gap features prefers models where the perturber is in the mass range of 1e6 Msun to 1e8 Msun. Orbital integrations back in time show that the stream encounter could not have been caused by any known globular cluster or dwarf galaxy, and mass, size and impact-parameter arguments show that it could not have been caused by a DM substructure, like those predicted to populate galactic haloes in LCDM cosmology. However, the expected densities of LCDM sub haloes in this mass range and in this part of the MW are 2-3 sigma lower than the inferred high density of the GD-1 perturber. This observation opens up the possibility that detailed observations of streams could measure the mass spectrum of DM substructures and even identify individual substructures and their orbits in the Galactic halo.
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