Day 927

Friday.


1507.04353
Detection of satellite remnants in the Galactic halo with Gaia III. Detection limits for Ultra Faint Dwarf Galaxies
Antoja, et al

Present a method to identify UFDG candidates in the halo of the MW using the future Gaia catalogue and explore its detection limits and completeness.  The method is based on the Wavelet Transform and searches for over-densities in the combined space of sky coordinates and proper motions, using kinematics in the search for the first time.  Test the method with a Gaia mock catalogue that has the Gaia Universe Model Snapshot (GUMS) as a background, and use a library of around 30k UFDGs simulated as Plummer spheres with a single stellar population.  For the UFDGs, use a wide range of structural and orbital parameters that go beyond the range spanned by real systems, where some UFDGs may remain undetected.  Characterize the detection limits as function of the number of observable stars by Gaia in the UFDGs with respect to that of the background and their apparent sizes in the sky and proper motion planes.  Find that the addition of proper motions in the search improved considerably the detections compared to a photometric survey at the same magnitude limit.  The experiments suggest that Gaia will be able to detect UFDGs that are similar to some of the known UFDGs even if the limit of Gaia is around 2 mags brighter than that of SDSS, with the advantage of having full-sky catalogue.  Also see that Gaia could even find some UFDGs that have lower surface brightness than the SDSS limit.


1507.04356
Clustering properties of $g$-selected galaxies at $z\sim0.8$
Favole, et al

Current and future large redshift surveys, as SDSS IV eBOSS or DESI, will use emission line galaxies (ELG) to probe cosmological models by mapping the LSS of the universe in 0.6<z<1.7.  With current data, explore the halo-galaxy connection by measuring 3 clustering properties of g-selected ELGs as matter tracers in the range 0.6<z<1: (i) the z-space 2PCF using spectroscopic redshifts from the BOSS ELG sample and VIPERS; (ii) the angular 2PCF on the footprint of the CFHT-LS; (iii) the gg lensing signal around the ELGs using the CFHTLenS.  Interpret these observations by mapping them onto the latest high-resolution MultiDark Planck N-body simulation, using a novel (Sub)Halo-Abundance Matching technique that accounts for the ELG incompleteness.  ELGs at z~0.8 live in halos of (1±0.5)e12Msun/h and 22.5±2.5% of them are satellites belonging to a larger halo.  The halo occupation distribution of ELGs indicates that the sampled galaxies are those in which stars form in the most efficient way, according to their stellar-to-halo mass ratio.


1507.04362
An origin for multi-phase gas in galactic winds and halos
Thompson, Quataert, Zhang, Weinberg

The origin of high velocity cool gas seen in galactic winds remains unknown.  Following Wang 1995, argue that rapid radiative cooing in initially host (1e7-8 K) thermally-driven outflows can produce fast neutral atomic and photoionzed cool gas.  Outflows with hot gas mass-loading factor relative to star formation rate of beta>0.5 cool on scales ranging form the size of the host to tens of kpc.  Provide scalings for the cooling radius r_cool, density, column density, emission measure, radiative efficiency, and cool gas velocity.  At r_cool, the gas produces X-ray and then UV/optical line emission at velocities of hundreds to thousands of km/s with a total power bounded from above by the energy injection rate 0.01 L_star if the flow is powered by steady-state star formation with luminosity L_star.  The wind is thermally and convectively unstable at and beyond r_cool.  Thermal instability can amplify density fluctuations by a factor of ~100, potentially leading to a multi-phase medium.  Cooled winds can decelerate in the extended gravitational potential of galaxies and may explain the prevalence of cool gas in galactic halos.  Forward a picture of winds whereby cool clouds are initially accelerated from the host by ram pressure of the hot flow, but are rapidly shredded and incorporated into the hot flow by the Kelvin-Helmholtz instability.  This increases the hot wind mass loading, seeding radiative and thermal instability and cool gas rebirth.  Show that if the cooled wind re-shocks as it sweeps up the circumgalactic medium that its cooling time is short, thus depositing cool gas far out into the halo. Finally, show that conduction can dominate energy transport in low-beta hot galactic winds, leading to much flatter temperature profiles compared to the nominal expectation from adabaticity, potentially consistent with X-ray observations of some local starbursts (Abridged)


1507.04363
Probing cosmology and gravity with redshift-space distortions around voids
Hamaus, Sutter, Laaux, Wandelt

Cosmic voids in the LSS of the universe affect the peculiar motions of objects in their vicinity.  Although these motions are difficult to observe directly, the clustering pattern of their surrounding tracers in z space is influenced in a unique way.  This allows to investigate the interplay between densities and velocities around voids, which is solely dictated by the laws of gravity.  With the help of N-body simulations and derived mock-galaxy catalogs, calculate the average density fluctuations inside and outside voids identified with a watershed algorithm in z-space and compare the results with the expectation from general relativity and the LCDM model of cosmology.  Find that simple linear-theory predictions work remarkably well in describing the dynamics of voids even on relatively small scales.  Adopting a Bayesian inference framework, determine the full posterior probability distribution of the model parameters and forecast the achievable accuracy on measurements of the growth rate of structure and the geometric distortion through the Alcock-Paczynski effect.  Their relative uncertainties in galaxy surveys with number densities comparable to the SDSS MAIN (CMASS) sample that probe a volume of 1(Gpc/h)^3 yield sigma_f/b/(f/b)~40%(60%) and sigma_DAH/D_AH ~ 5% (8%), respectively.  The presented method is highly model independent; its viability lies in the underlying assumption of statistical isotropy of the universe.


1507.04365
What is the optimal way to measure the galaxy power spectrum?
Smith, Marian

Measurements of the galaxy power spectrum contain a wealth of information about the Universe.  Its optimal extraction is vital if we are to truly understand the micro-physical nature of DM and DE.  In Smith&Marian2015, they generalized the PS methodology of Feldman+94 to take into account the key tenets of galaxy formation: galaxies form and reside exclusively in DM haloes; a given DM halo may host galaxies of various luminosities; galaxies inherit the LS bias associated with their host halo.  In this paradigm, derive the optimal weighting and reconstruction scheme for maximizing the S/N on a given band power estimate.  For a future all-sky flux-limited galaxy redshift survey of depth b_J~22, now demonstrate that the optimal weighting scheme does indeed provide improved S/N at the level of ~20% when compared to Feldman+94 and ~60% relative to Percival+2003, for scales of order k~0.5 Mpc/h [inverse?].  Using a Fisher matrix approach, show that the cosmological information yield is also increased relative to these alternate methods - especially the primordial PS amplitude and dark energy equation of state.


1507.04376
LoCuSS: exploring the selection of faint blue background galaxies for cluster weak-lensing
Ziparo, Smith, Okabe, Haines, Pereira, Egami

Cosmological constraints from galaxy clusters rely on accurate measurements of mass and internal structure of clusters.  An important source of systematic uncertainty in cluster mass and structure measurements is the secure selection of background galaxies that are gravitationally lensed by clusters.  This issue has been shown to be particularly severe for faint blue galaxies.  Therefore explore the selection of faint blue background galaxies, by reference to photometric redshift catalogs derived from the COSMOS survey and the observations of massive galaxy clusters at z~0.2.  Show that methods relying on photometric redshifts of galaxies in/behind clusters based on observations through five filters, and on deep 30-band COSMOS photometric redshifts are both inadequate to identify safely faint blue background galaxies.  This is due to the small number of filters used by the former, and absence of massive galaxy clusters at redshifts of interest in the latter.  Therefore develop a pragmatic method to combine both sets of photometric redshifts to select a population of blue galaxies based purely on photometric analysis.  This sample yields stacked WL results consistent with the previously published results based on red galaxies.  Also show that the stacked cluster centric number density profile of these faint blue galaxies is consistent with expectation from consideration of the lens magnification signal of the clusters.  Indeed, the observed number density of blue background galaxies changes by ~10-30% across the radial range over which other surveys assume it to be flat.


1507.04385
CLASH: joint analysis of strong-lensing, weak-lensing shear and magnification data for 20 galaxy clusters
Umetsu, Zitrin, Gruen, Merten, Donahue, Postman

Present a comprehensive analysis of SL, WL shear and magnification data for a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters selected form the CLASH survey.  The analysis combines constraints from 16-band HST observations and wide-field multi-color imaging taken primarily with Subaru/Suprime-Cam.  Reconstruct surface mass density profiles of individual clusters from a joint analysis of the full lensing constraints, and determine masses and concentrations for all clusters.  Find internal consistency of the ensemble mass calibration to be <5±6% by comparison with the CLASH WL-only measurements of Umetsu+.  For the X-ray selected subsample, examine the concentration-mass relation and its intrinsic scatter using a Bayesian regression approach.  The model yields a mean concentration of c(z=0.34)=3.95±0.35 at M_200c~14e14Msun and an intrinsic scatter of sigma(ln c_200c) = 0.13±0.06, in excellent agreement with LCDM predictions when the CLASH selection function based on X-ray morphological regularity and the projection effects are taken into account.  Also derive an ensemble-averaged surface mass density profile for the X-ray selected subsample by stacking their individual profiles.  The stacked mass profile is well described by a family of density profiles predicted for cusp DM-dominated halos, namely, the NFW, Einasto, and DARKexp models, whereas the single power-law, cored isothermal and Burkert density profiles are disfavored by the data.  Show that cusp halo models that include the two-halo term provide improved agreement with the data.  For the NFW halo model, measure a mean concentration of c_200c=3.79±0.30 at M_200c=14.1±1.0e14 Msun, demonstrating robust consistency between complementary analysis methods.


1507.04493
LoCuSS: weak-lensing mass calibration of galaxy clusters
Okabe, Smith

Present WL mass measurements of 50 X-ray luminous galaxy clusters at 0.15<z<0.3, based on high quality observations with Suprime-Cam counted on the 8.2m Subaru telescope.  Pay close attention to possible systematic biases, aiming to control them at the <4% level.  The dominant source of systematic bias in WL measurements of the mass of individual galaxy clusters is contamination of background galaxy catalogues by faint cluster and foreground galaxies.  Extend the conservative method for selecting background galaxies with (V-i') colors redder than the red sequence of cluster members to use a color-cut that depends on cluster-centric radius.  This allows definition of background galaxy samples that suffer <1% contamination, and comprise 13 galaxies per square arc minute.  Thanks to the purity of the background galaxy catalogue, the largest systematic in the measurement is a shape measurement bias of  3%, that using custom-made simulations that probe weak shears up to g=0.3.  The individual cutler mass and concentration measurements are in excellent agreement with predictions of the mass-concentration relation.  Equally, the stacked shear profile is in excellent agreement with the NFW profile.  The new LoCuSS mass measurements are consistent with the CCCP and CLASH surveys, and in tension with the Weighing the Giants (WtG) at ~2sigma significance.