Day 1266

Thursday.

1705.10852
Resolving the era of river-forming climates on Mars using stratigraphic logs of river-deposit dimensions
Kite, Howard, Lucas, Lewis

River deposits are one of the main lines of evidence that tell us that Mars once had a climate different from today, and so changes in river deposits with time tell us something about how Mars climate changed with time.  In this study, focus in on one sedimentary basin - Aeolis Dorsa - which contains an exceptionally high number of exceptionally well-preserved river deposits that appear to have formed over an interval of >0.5 Myr.  Use changes in the river deposits' scale with stratigraphic elevation as a proxy for changes in river paloedischarge.  Meander wavelengths tighten upwards and channel widths narrow upwards, and there is some evidence for a return to wide large-wavelength channels higher in the stratigraphy.  Meander wavelength and channel width covary with stratigraphic elevation.  The factor of 1.5-2 variations in paleochannel dimensions with stratigraphic elevation correspond to ~2.6-fold variability in bank-forming discharge (using standard wavelength-discharge scalings and width-discharge scalings).  Taken together with evidence from a marker bed for discharge variability at ~10m stratigraphic distances, the variation in the scale of river deposits indicates that bank-forming discharge varied at both 10m stratigraphic (1e2-1e6 yr) and ~100m stratigraphic (1e3 - 1e9 yr) scales.  Changing sediment input leading to a change in characteristic slopes and/or drainage area could be responsible, and another possibility is changing climate (±50 W/m^2 in peak energy available for snow/ice melt).


1705.11167
The ellipticity of galaxy cluster halos from satellite galaxies and weak lensing
Shin, Clampitt, Jain, Bernstein, Neil, Rozo, Rykoff

Study the ellipticity of galaxy cluster halos as characterized by the distribution of cluster galaxies and as measured with weak lensing.  Use monte-carol sims of projected, elliptical cluster density profiles to estimate and correct for several biases that arise in using cluster satellite galaxies.  The primary biases are Poisson noise bias (due to the finite number of satellites), edge bias (due to the cluster edge) and projection effects.  Correct these biases for clusters with different richness.  Apply the methodology to 10,428 SDSS clusters identified by the redMaPPer algorithm with richness above 20.  Find a mean ellipticity = 0.265±0.002 (stat) ±0.031 (syst.) corresponding to an axis ratio = 0.580±0.02(stat)±0.040(syst).  The dominant contribution to the systematic uncertainty comes from the uncertainty in the number of interlopers in the redMaPPer cluster sample.  Compare this ellipticity of the satellites to the halo shape, through a stacked lensing measurement using optimal estimators of the lensing quadrupole based on Clampitt and Jain (2016).  Find a best-fit axis ratio of 0.55±0.09, consistent with the satellite ellipticity.  Thus cluster galaxies trace the shape of the DM halo to within the estimated uncertainties.  Finally, restack the satellite and lensing ellipticity measurements along the major axis of the cluster central galaxy's light distribution.  From the lensing measurements, infer a misalignment angle with an RMS of 30 deg when stacking on the central galaxy.  Discuss applications of halo shape measurements to test the effects of the baryonic gas and AGN feedback, as well as DM and gravity.  The major improvements in S/N expected with the ongoing DES and future surveys from LSST, Euclid and WFIRST will make halo shapes a useful probe of these effects.

Day 1265

Wednesday.

1705.10321
Gas kinematics, morphology, and angular momentum in the FIRE simulations
El-Badry, et al

Study the z=0 gas kinematics, morphology, and angular momentum content of isolated galaxies in a suite of cosmological zoom-in simulations from the FIRE project spanning M*=1e6-10 Msun.  Gas becomes increasingly rotationally supported with increasing galaxy mass.  In the lowest-mass galaxies (M*<1e8 Msun), gas fails to form a morphological disk and is primarily dispersion and pressure supported.  At intermediate masses (M*=1e8-10 Msun), galaxies display a wide range of gas kinematics and morphologies, from thin, rotating disks, to irregular spheroids with negligible net rotation.  All the high-mass (M*=1e10-11 Msun) galaxies form rotationally supported gas disks.  Many of the halos whose galaxies fail to form disks harbor reservoirs of high angular momentum gas in their circumgalactic medium.  The ratio of the specific angular momentum of gas in the central galaxy to that of the DM halo increases significantly with galaxy mass, from j_gas/j_DM~0.1 to j_gas/j_DM~2 at M*=1e10-11 Msun.  The reduced rotational support in the lowest-mass galaxies owes to (a) stellar feedback and the UV background suppressing the accretion of high-angular momentum gas at late times, and (b) stellar feedback driving large non-circular gas motions.  Broadly reproduce the observed scaling relations between galaxy mass, gas rotation velocity, size and angular momentum, but may somewhat under predict the incidence of disky, high-angular momentum galaxies at the lowest masses (M*=1e6 to 2e7 Msun).  In the simulations, stars are uniformly less rotationally supported than gas.  The common assumption that stars follow the same rotation curve as gas thus substantially overestimates galaxies' stellar angular momentum, particularly at low masses.

Day 1264

Friday.  Monday.  Tuesday.

1705.10031
An evaluation of cosmological models from expansion and growth of structure measurements
Zhai, Blanton, Slosar, Tinker

Compare a large suite of theoretical cosmological models to observational data from the CMB, BAO measurements of expansion, Type Ia SNe measurements of expansion, z-space distortion measurements of the growth of structure, and the local Hubble constant. The theoretical models include parameterizations of DE as well as physical models of DE and modified gravity.  Determine the constraints on the model parameters, incorporating the z space distortion data directly in the analysis.  To determine whether models can be ruled out, evaluate the p value (the probability under the model of obtaining data as bad or worse than the observed data).  In the comparison, find the well known tension of H0 with the other data; no model resolves this tension successfully.  Among the models considered, the LS growth of structure data does not affect the modified gravity models as a category particularly differently than DE models; it matters for some modified gravity models but not others, and the same is true for DE models.  Compute predicted observables for each model under current observational constraints, and identify models for which future observational constraints will be particularly informative.


1705.10256
The extragalactic background might revisited and the cosmic photon-photon opacity
Franceschini, Rodighiero

In addition to its relevant astrophysical and cosmological significance, the Extragalactic Background Light (EBL) is a fundamental source of opacity for cosmic high energy photons, as well as a limitation for the propagation of high-energy particles in the Universe.  Review the previously published determinations of the EBL photon density in the Universe and its evolution with cosmic time, in the light of recent surveys of IR sources at long wavelengths.  Exploit deep survey observations by Herschel and Spitzer, matched to optical and NIR photometric and spectroscopic data, to re-estimate number counts and luminosity functions longwords of a few microns, and the contribution of resolved sources to the EBL.  These new data indicate slightly lower photon densities in the mid- and far-infrared and sub-millimeter compared to previous determinations.  This implies slightly lower cosmic opacity for photon-photon interactions.  The new data do not modify previously published EBL modeling in the UV-optical and near-IR up to several microns, while reducing the photon density at longer wavelengths.  This improved model of the EBL alleviates some tension that had emerged in the interpretation of the highest-energy TeV observations of local blazers, reducing the case for new physics beyond the standard model (e.g. violations of the Lorenz Invariance, LIV, at the highest particles energies), or for exotic astrophysics, that had sometimes been called for to explain it.  Applications of this improved EBL model on current data are considered, as well as perspectives for future instrumentation, the Cherenkov Telescope Array (CTA) in particular.

Day 1263

Wednesday.  Thursday.

1705.08513
Extensive globular cluster systems associated with ultra diffuse galaxies in the Coma cluster
van Dokkum, et al

Present HST imaging of 2 UDGs with measured stellar velocity dispersions in the Coma cluster.  The galaxies, Dragonfly 44 and DFX1, have effective radii of 4.7 kpc and 3.5 kpc and velocity dispersions of 47±8 km/s and 30±7 km/s, respectively.  Both galaxies are associated with a striking number of compact objects, tentatively identified as globular clusters: N_gc=74±18 for Dragonfly 44 and N_gc = 62±17 for DFX1.  The number of globular clusters is far higher than expected from the luminosities of the galaxies but is consistent with expectations from the empirical relation between dynamical mass and globular cluster count defined by other galaxies.  Combining the data for these 2 objects with previous HST observations of Coma UDGs, find that most have large globular cluster populations for their luminosities, in contrast to a recent study of a similar sample by Amorisco+2017, but consistent with earlier results for individual galaxies. The Harris+2017 relation between globular cluster count and DM halo mass implies a median halo mass of M_halo~1.5e11 Msun for the 16 Com UDGs that have been observed with HST so far, with the largest and brightest having M_halo~5e11 Msun.

Day 1262

Tuesday.

1705.07596
Galaxy and Mass Assembly: the evolution of the cosmic spectral energy distribution from z=1 to z=0
Andrews, Driver, et al

Present the evolution of the Cosmic Spectral Energy Distribution (CSED) from z=1-0.  The CSEDs originate from stacking individual SED fits based on panchromatic photometry from GAMA and COSMOS datasets in 10 redshift intervals with completeness corrections applied.  Below z=0.45, have credible SED fits from 100nm to 1mm.  Due to the relative low sensitivity of the far-infrared data, the far-infrared CSEDs contain a mix of predicted and measured fluxes above z=0.45.  The results include appropriate errors to highlight the impact of these corrections.  Show that the bolometric energy output of the Universe has declined by a  factor of roughly four -- from 5.1±1.0 at z~1 to 1.3±0.3e35 h_70 W Mpc^-3 at the current epoch.  Show that this decrease is robust to cosmic variance, SED modeling and other various types of error.  The CSEDs are also consistent with an increase in the mean age of stellar populations.  Also show that dust attenuation has decreased over the same period, with the photon escape fraction at 150 nm increasing from 16±3 at z~1 to 24±5% at the current epoch, equivalent to a decrease in A_FUV of 0.4 mag.  The CSEDs account for 68±12 and 61±13 % of the cosmic optical and IR backgrounds respectively as defined from integrated galaxy counts and are consistent with previous estimates of the cosmic infrared background with redshift.


1705.07843
Imprints of reionization in galaxy clustering
Schmidt, Beutler

Reionization, the only phase transition in the Universe since recombination, is a key event in the cosmic history of baryonic matter.  Derive, in the context of the LS bias expansion, the imprints of the epoch of reionization in the LS distribution of galaxies, and identify two contributions of particular importance.  Fist, the Compton scattering of CMB photons off the free electrons lead to a drag force on the baryon fluid.  This drag induces a relative velocity between baryons and CDM which is of the same order of magnitude as the primordially-induced relative velocity, and enters in the evolution of the relative velocity as calculated by Boltzmann codes.  This leads to a unique contribution to galaxy bias involving the matter velocity squared.  The second important effect is a modulation of the galaxy density by the ionizing radiation field through radiative transfer effects, which is captured in the bias expansion by so-called higher-derivative terms.  Constrain both of these imprints using the power spectrum of the BOSS DR12 galaxy sample.  While they do not lead to a shift in the baryon acoustic oscillation scale, including these terms is important for unbiased cosmology constraints from the shape of the galaxy power spectrum.

Day 1261

Monday.

1705.06745
The first-year shear catalog of the Subaru Hyper Suprime-Cam SSP Survey
Mandelbaum, Miyatake, Hamana, Oguri, Simet, Armstrong, Bosch, et al

Present and characterize the catalog of galaxy shape measurements that will be used for cosmological WL measurements in the Wide layer of the first year of HSC survey.  The catalog covers an area of 136.9 deg^2 split into 6 fields, with a mean i-band seeing of 0.58" and 5 sigma point-source depth of i~26.  Given conservative galaxy selection criteria for first year science, the depth and excellent image quality results in unweighted and weighted source number densities of 24.6 and 21.8 arcmin^-2, respectively.  PSF modeling is carried out on individual exposures, while galaxy shapes are measured in a linear coaddition.  Define the requirements for cosmological WL science with this catalog, characterize potential systematics in the catalog using a series of internal null tests for problems with PSF modeling, shear estimation, and other aspects of the image processing, and describe systematics tests using 2 different sets of image simulations.  Finally, discuss the dominant systematics and the planned algorithmic changes to reduce them in future data reductions.


1705.06766
The Hyper Suprime-Cam Software Pipeline
Bosch, Armstrong, et al

Describe the optical imaging data processing pipeline developed for HSC.  The HSC Pipeline builds on the prototype pipeline begin developed by LSST Data Management system, adding customization for HSC, LS processing capabilities, and novel algorithms that have since been reincorporated into the LSST codebase.  While designed primarily to reduce HSC SSP data, it is also the recommended pipeline for reducing general-observer HSC data.  The HSC pipeline includes high level processing steps that generate coadded images and science-read catalogs as well as low-level detrending and image characterizations.


1705.06792
Two- and three-dimensional wide-field weak lensing mass maps from the Hyper Suprime-Cam Subaru Strategic Program S16A data
Oguri, Miyazaki, Hikage, et al

Present wide-field (167 deg^2) weak lensing mass maps from the HSC-SSP.  Compare these WL based DM maps with maps of the distribution of the stellar mass associated with luminous red galaxies.  Find a strong correlation between these 2 maps with a correlation coefficient of rho=0.54±0.03 (for a smoothing size of 8').  This correlation is detected even with a smaller smoothing scale of 2' (rho-0.34±0.01).  This detection is made uniquely possible because of the high source density of the HSC-SSP WL survey (near~25 armin^-2).  Also present a variety of tests to demonstrate that the maps are not significantly affected by systematic effects.  By using the photometric redshift information associated with source galaxies, reconstruct a 3D mass map.  This 3D mass map is also found to correlate with the 3D galaxy mass map.  Cross-correlation tests presented in this paper demonstrate that the HSC-SSP WL mass maps are ready for further science analyses.


1705.06852
Multiwavelength study of X-ray Luminous Clusters i the Hyper Suprime-Cam Subaru Strategic Program S16A field
Miyaoka, et al

Present a joint X-ray, optical and WL analysis for X-ray luminous galaxy clusters selected within the MCXC cluster catalog in the HSC-SSP survey field with S16A data.  Measure hydrostatic equilibrium (H.E.) masses using XMM-Newton data for a sample of four MCXC clusters in the current coverage area.  Additionally analyze a non-MCXC cluster associated with one MCXC cluster to calibrate the X-ray analysis.  Show that H.E. masses for the MCXC clusters are correlated with cluster richness from the CAMIRA catalog (Oguri+2017), while that for the non-MCXC cluster deviates from the scaling relation.  The mass normalization of the relationship between the cluster richness and H.E. mass is compatible with one inferred by matching CAMIRA cluster abundance with a theoretical halo mass function.  The mean gas mass fraction based on H.E. masses for the MCXC clusters is <f_gas> = 0.126±0.010 at spherical overdensity Delta=500, which is ~80-90 % of the cosmic mean baryon fraction, Omega_b/Omega_m, measured by CMB experiments.  Find that the mean baryon fraction estimated from X-ray and HSC-SSP optical data is comparable to Omega_b/Omega_m.  A WL shear catalog of BG galaxies, combined with photo-z, is currently available only for 3 clusters in the sample.  Hydrostatic equilibrium masses roughly agree with WL masses, albeit with large uncertainty.  This study demonstrates that the multi wavelength study using X-ray, HSC-SSP optical and WL data will enable understanding of cluster physics and utilize cluster-based cosmology.

Day 1260

Friday.

1705.06347
The galaxy clustering crisis in abundance matching
Campbell, van den Bosch, Padmanabhan, et al

Galaxy clustering on small scales is significantly under-predicted by sub-halo abundance matching (SHAM) models that populate (sub-) haloes with galaxies based on peak halo mass, M_peak.  SHAM models based on the peak maximum circular velocity, V_peak, have had much better success.  The primary reason M_peak based models fail is the relatively low abundance of satellite galaxies produced in these models compared to those based on V_peak.  Despite success in predicting clustering, a simple V_peak based SHAM model results in predictions for galaxy growth that are at odds with observations.  Evaluate 3 possible remedies that could "save" mass-based SHAM: (1) SHAM models require a significant population of "orphan" galaxies as a realist of artificial disruption/merging of sub-haloes in modern high resolution DM simulations; (2) satellites must grow significantly after their accretion; and (3) stellar mass is significantly affected by halo assembly history.  No solution is entirely satisfactory.  However, regardless of the particulars, show that popular SHAM models based on M_peak cannot be complete physical models as presented.  Either V_peak truly is a better predictor of stellar mass at z~0 and it remains to be seen how the correlation between stellar mass and V_peak comes about, or SHAM models are missing vital component(s) that significantly affect galaxy clustering.

Day 1259

Thursday.

1705.05843
HICOSMO - Cosmology with a complete sample of galaxy clusters: II. Cosmological results
Schnellenberger, Reiprich

The growth of structure in the Universe is tightly correlated with the cosmological parameters.  Galaxy clusters as tracers of the LSS are the ideal objects to witness this evolution.  The X-ray bright, hot gas in the potential well of a galaxy cluster enables systematic X-ray studies of samples of galaxy clusters to constrain cosmological parameters.  HIFLUGCS consists of the 64 X-ray brightest clusters in the Universe, building up a local sample of galaxy clusters.  Here, utilize this sample to determine individual hydrostatic mass estimates for all the clusters of the sample, and by making use of the completeness of the sample, quantify constraints on the 2 interesting cosmological parameters, OmegaM and sigma8.  Paper I describes the data analysis procedure and the compares the individual mass estimates with other references.  Here, apply the total hydrostatic and gas mass estimates from the X-ray analysis to a Bayesian cosmological likelihood analysis and leave several parameters fee to be constrained.  Find OmegaM=0.30±0.01 and sigma8=0.79±0.03 (statistical uncertainties, 68% CL) using the default analysis strategy combining both, a mass function analysis and the gas mass fraction results.  The main sources of biases that also corrected here are (1) the influence of galaxy groups, (2) the hydrostatic mass bias, (3) the extrapolation of the total mass, (4) the theoretical halo mass function and (5) other physical effects.  Find that galaxy groups introduce a strong bias, since their number density seems to be overpredicted by the halo mass function.  On the other hand, baryonic effects as incorporated by recent hydrodynamical simulations do not result in a significant change in the constraints.  The total systematic uncertainties (20%) clearly dominate the statistical uncertainties on cosmological parameters.

Day 1258

Wednesday.

1705.05442
Optimized clustering estimators for BAO measurements accounting for significant redshift uncertainty
Ross, et al

Determine an optimized clustering statistic to be used for galaxy samples with significant redshift uncertainty, such as those that rely on photometric redshifts.  To do so, study the BAO information content as a function of the orientation of galaxy clustering modes with respect to their angle to the LOS.  The clustering along the LOS, as observed in a redshift-space with significant redshift uncertainty, has contributions from clustering modes with a range of orientations with respect to the true LOS.  For z uncertainty sigma_z>=0.02(1+z), find that while the BAO information is confined to transverse clustering modes in the true space, it is spread nearly evenly in the observed space.  Thus, measuring clustering in terms of the projected separation (regardless of the LOS) is an efficient and nearly lossless compression of the signal for sigma_z>=0.02(1+z).  For reduced z uncertainty, a more careful consideration is required.  Use more than 1700 realizations of galaxy simulations mimicking the DES Year1 sample to validate the analytic results and optimized analysis procedure.  Find that using the correlation function binned in projected separation, can achieve uncertainties that are within 10% of those predicted by Fisher matrix forecasts.  Predict that DES Y1 should achieve a 5% distance measurement using the optimized methods.  Expect the results presented here to be important for any future BAO measurements made using photo-z data.

Day 1257

Tuesday.

1507.05022
Efficient evaluation of cosmological angular statistics
Assassi, Simonović, Zaldarriaga

Angular statistics of cosmological observables are hard to compute.  The main difficulty is due to the presence of highly-oscillatory Bessel functions which need to be integrated over.  In this paper, provide a simple and fast method to compute the angular power spectrum and bispectrum of any observable.  The method is based on using an FFTlog algorithm to decompose the momentum-space statistics onto a basis of power-law functions.  For each power law, the integrals over Bessel functions have a simple analytical solution.  This allows efficient evaluations of these integrals, independently of the value of the multipole ell.  Apply this general method to the galaxy, lensing and CMB temperature angular power spectrum and bispectrum.

Day 1256

Monday.

1705.04327
The immitigable nature of assembly bias: the impact of halo definition on assembly bias
Villarreal, Zentner, et al

DM halo clustering depends not only on halo mass, but also on other properties such as concentration and shape.  This phenomenon is known broadly as assembly bias.  Explore the dependence of assembly bias on halo definition, parameterized by spherical overdensity parameter, Delta.  Summarize the strength of concentration-, shape- and spin-dependent halo clustering as a function of halo mass and halo definition.  Concentration-dependent clustering depends strongly on mass at all Delta.  For conventional halo definitions (Delta ~ 200m-600m), concentration-dependent clustering at low mass is driven by a population of haloes that is altered through interactions with neighboring haloes.  Concentraiton-dependent clustering can be greatly reduced through a mass-dependent halo definition with Delta ~ 20m-40m for haloes with M_200m<~1e12 Msun/h.  Smaller Delta implies larger radii and mitigates assembly bias at low mass by subsuming altered, so-called backsplash haloes into now larger host haloes.  At higher masses (M_200m.~1e13 Msun/h) larger over densities, Delta>~600m, are necessary.  Shape- and spin-dependent clustering are significant for all halo definitions that is explored and exhibit a relatively weaker mass dependence.  Generally, both the strength and the sense of assembly bias depend on halo definition, varying significantly even among common definitions.  Identify no halo definition that mitigates all manifestations of assembly bias.  A halo definition that mitigates assembly bias based on one halo property (e.g., concentration) must be mass dependent.  The halo definitions that best mitigate concentration-dependent halo clustering do not coincide with the expected average splash back radii at fixed halo mass.

Day 1255

Wednesday.  Thursday.  Friday.

1705.03888
Beyond assembly bias: exploring secondary halo biases for cluster-size halos
Mao, Zentner, Wechsler

Secondary halo bias, commonly known as "assembly bias," is the dependence of halo clustering on halo property other than mass. This prediction of the LCDM cosmology is essential to modeling the galaxy distribution to high precision and interpreting clustering measurements.  As the name suggests, different manifestations of secondary halo bias have been thought to originate from halo assembly histories.  Show conclusively that this is incorrect for cluster-size halos.  Present an up-to-date summary of secondary halo biases of high-mass haloes due to various halo properties including concentration, spin, several proxies of assembly history, and sub halo properties.  While concentration, spin and the abundance and radial distribution of sub haloes exhibit significant secondary biases, properties that directly quantify halo assembly history do not.  In fact, the entire assembly histories of haloes in pairs are nearly identical to those of isolated haloes.  In general, a global correlation between two halo properties does not predict whether or not these two properties exhibit similar secondary biases.  For example, assembly history and concentration (or sub halo abundance) are correlated for both paired and isolated haloes, but follow slightly different conditional distribution in these two cases.  This results in a secondary halo bias due to concentration (or sub halo abundance), despite the lack of assembly bias in the strict sense for cluster-size haloes.  Due to this complexity, caution must be exercised in using any one halo property as a proxy to study the secondary bias due to another property.


1705.04074
Galaxy and Mass Assembly (GAMA): The galaxy stellar mass function to $z=0.1$ from the r-band selected equatorial regions
Wright, Robotham, Driver, et al

Derive the low redshift galaxy stellar mass function (GSMF), inclusive of dust corrections, for the equatorial GAMA dataset covering 180 deg^2.  Construct the mass function using a density-corrects maximum volume method, using masses corrected for the impact of optically thick and thin dust.  Explore the galactic bivariate brightness plane (M*-mu), demonstrating that surface brightness effects do not systematically bias the mass function measurement above 1e7.5 Msun.  The galaxy distribution in the M-mu-plane appears well bounded, indicating that no substantial population of massive but diffuse or highly compact galaxies are systematically missed due to the GAMA selection criteria.  The GSMF is {fit with} a double Schechter function, with M*=1e10.78 Msun, phi1*=2.93e-3 h^3/Mpc^3, alpha1=-0.62, phi2*=0.63e-3 h^3/Mpc^3, and alpha2=-1.50.  Find the equivalent faint end slope as previously estimated using the GAMA-I sample, although find a higher value of M*.  Using the full GAMA-II sample, able to fit the mass function to masses as low as 1e7.5Msun, and assess limits to 1e6.5 Msun.  Combining GAMA-II with data from G10-COSMOS, able to comment qualitatively on the shape of the GSMF down to masses as low as 1e6 Msun.  Beyond the well known upturn seen in the GSMF at 1e9.5 the distribution appears to maintain a single power-law slope from 1e9 to 1e6.5.  Calculate the stellar mass density parameter given the best-estimate GSMF, finding Omega*=1.66e-3/h, inclusive of random and systematic uncertainties. [h == h_70, errorbars omitted]

Day 1254

Tuesday.

1705.02420
Reconstructing the gravitational field of the local universe
Desmond, Ferreira, Lavaux, Jasche

Tests of gravity at the galaxy scale are in their infancy.  As a first step to systematically uncovering the gravitational significance of galaxies, map 3 fundamental gravitational variables -- the Newtonian potential, acceleration and curvature -- over the galaxy environments of the local universe to a distance of approximately 200 Mpc.  The method combines the contributions from galaxies in an all-sky redshift survey, haloes from an N-body simulation hosting low-luminosity objects, and linear and quasi-linear modes of the density field.  Use the ranges of these variables to determine the extent to which galaxies expand the scope of generic tests of gravity and are capable of constraining specific classes of model for which they have special significance.  Finally, investigate the improvements afforded by upcoming galaxy surveys.


1705.02629
Testing the accuracy of clustering redshift with simulations
Scottez, Benoit-Lévy, Coupon, Ilbert, Mellier

Explore the accuracy of the clustering-based redshift inference within the MICE2 simulation.  This method uses the spatial clustering of galaxies between a spectroscopic reference sample and an unknown sample.  The goal of this study is to give a preview of the redshift accuracy one can reach with this method.  To do so, first highlight the requirements of this technique in terms of number of objects in both the reference and unknown samples.  Also confirm that this method does not require a representative spectroscopic sample for calibration.  Estimate that a density of spectroscopic objects of 1e-5 arcmin^-2 per redshift bin of width delta_z=0.01 over 9000 deg^2 allows to reach 0.1% accuracy in the man redshift for a galaxy density compatible with next generation of cosmological surveys.  This number is compatible with the density of QSOs in BOSS.  Second, demonstrate the ability to measure individual redshifts for galaxies independently from the photo-z procedure.  The resulting individual clustering redshifts have a bias =-0.001, an outlier fraction of eta=2.57% and a scatter of sigma=0.027 to i<25.  The advantage of this procedure is 3-fold: i) it allows the use of clustering redshifts for any field in astronomy, ii) it allows the possibility to combine photometric and clustering based z to get an improved redshift estimation, iii) it allows the use of cluster-z to define tomographic bins for weak lensing.  Finally, explore this last option and build 5 clustering z selected tomographic bins from redshift 0.2 to1.  Found a bias on the man redshift estimate of 0.002 per bin.

Day 1253

Monday.

1705.01988
Revisiting HOD model assumptions: the impact of AGN feedback and assembly bias
McCullagh, Norberg, Cole, Gonzalez-Perez, Baugh, Helly

The standard HOD models were originally developed based on results from semi-analytic and hydrodynamical galaxy formation models.  Those models have since progressed, in particular to include AGN feedback to match the galaxy luminosity function in a universe with the observed baryon fraction.  AGN feedback affects the relationship between galaxy stellar mass and luminosity, in particular making the relationship non-monotonic.  For matched number density samples, galaxies in luminosity-threshed samples occupy a different range of halo masses from those in stellar-mass-threshold samples.  Find that the shapes of the HODs of luminosity-threshold samples are slightly more complicated in semi-analytic galaxy formation models that include AGN feedback than are assumed by standard HOD models.  Also find that sub halo abundance matching (SHAM) does not preserve these non-standard shapes.  Show that catalogues created using SHAM and the semi-analytic model Galform that have the same large-scale 2-pt clustering by construction have different void probability functions (VPFs) in both real and redshift space.  Find that these differences arise from the different HOD shapes, as opposed to assembly bias, which indicates that the VPF could be used to test the suitability of an HOD model with real data.


1705.02071
Properties and origin of galaxy velocity bias in the Illustris simulation
Ye, Guo, Zheng, Zehavi

Use the hydrodynamical galaxy formation simulations from the ILlustris suite to study the origin and properties of galaxy velocity bias, i.e., the difference between the velocity distributions of galaxies and dark matter inside halos.  Find that galaxy velocity bias is a decreasing function of the ratio of galaxy stellar mass to host halo mass.  In general, central galaxies are not at rest with respect to dark matter halos or the core of halos, with a velocity dispersion above 0.04 times that of the DM.  The central galaxy velocity bias is found to be mostly caused by the close interactions between the central and satellite galaxies.  For satellite galaxies, the velocity bias is related to their dynamical and tidal evolution history after being accreted onto the host halos.  It depends on the time after the accretion and their distances from the halo centers, with massive satellites generally moving more slowly than the dark matter.  The results are in broad agreements with those inferred from modeling small-scale redshift-space galaxy clustering data, and the study can help improve models of z-space galaxy clustering.

Day 1252

Thursday.  Friday.

1705.01109
An unbiased estimator for the ellipticity from image moments
Tessore

An unbiased estimator for the ellipticity of an object in a noisy image is given in terms of the image moments.  Three assumptions are made: i) the pixel noise is normally distributed, although with arbitrary covariance matrix, ii) the image moments are taken about a fixed centre, and iii) the point-spread function is known.  The relevant combinations of image moments are then jointly normal and their covariance matrix can be computed.  A particular estimator for the ratio of the means of jointly normal variates is constructed and used to provide the unbiased estimator of the ellipticity.  Furthermore, an unbiased estimate of the covariance of the new estimator is also given.


1705.01599
Characterization and photometric performance of the Hyper Suprime-Cam Software Pipeline
Huang, et al

The Subaru Strategic Program (SSP) is an ambitious multi-band survey using HSC on Subaru telescope.  The Wide layer of the SSP is both wide and deep, reaching a detection limit of i~26.0 mag.  At these depths, it is challenging to achieve accurate, unbiased, and consistent photometry across all 5 bands.  The HSC data are reduced using a pipeline that builds on the prototype pipeline for the LSST.  Developed a Python-based, flexible framework to inject synthetic galaxies into real HSC images called SynPipe.  Explain the design and implementation of SynPipe and generate a sample of synthetic galaxies to examine the photometric performance of the HSC pipeline.  For stars, achieve 1% photometric precision at i~19.0 mag and 6% precision at i~25.0 in the i-band.  For synthetic galaxies with single-Sersic profiles, forced CModel photometry achieves 13% photometric precision at i~20.0 mag and 18% precision at i~25.0 in the i-band.  Show that both forced PSF and Model photometry yield unbiased color estimates that are robust to seeing conditions.  Identify several caveats that apply to the version of HSC pipeline used for the first public HSC data release (DR1) that needs to be taking into consideration.  First, the degree to which an object is blended with other objects impacts the overall photometric performance.  This is especially true for point sources.  Highly blended objects tend to have larger photometric uncertainties, systematically underestimated fluxes and slightly biased colors.  Second, >20% of stars at 22.5<i<25.0 mag can be misclassified as extended objects.  Third, the current CModel algorithm tends to strongly underestimate the half-light radius and ellipticity of galaxy with i>21.5 mag.

Day 1251

Wednesday.

1704.08871
The faint end of the red sequence galaxy luminosity function: unveiling surface brightness selection effects with the CLASH clusters
Martinet, et al

Characterizing the evolution of the faint end of the cluster red sequence (RS) galaxy luminosity function (GLF) with z is a milestone in understanding galaxy evolution.  However, the community is still divided in that respect, hesitating between an enrichment of the RS due to efficient quenching of blue galaxies from z~1 to present-day or a scenario in which the RS is built at a higher z and does not evolve afterwards.  Recently, it has been proposed that surface brightness (SB) selection effects could possibly solve the literature disagreement, accounting for the diminishing of the RS faint population in ground based observations.  Investigate this hypothesis by comparing the RS GLFs of 16 CLASH clusters computed independently from ground-based Subaru/Suprime-Cam and HST/ACS images in the z range 0.187<=z<=0.686.  Stack individual cluster GLFs in z and mass bins.  Find similar RS GLFs for space and ground based data, with a difference 0.2 sigma in the faint end parameter alpha when stacking all clusters together and a maximum difference of 0.9 sigma in the case of the high z stack, demonstrating a weak dependence on the type of observations in the probed range of z and mass.  When considering the full sample, estimate alpha=-0.76±0.07 and alpha=-0.78±0.06 with HST and Subaru respectively.  Note a mild variation of the faint end with z at a 1.7 sigma and 2.6 sigma significance.  Investigate the effect of SB dimming by simulating the low z galaxies at high z.  Measure an evolution in the faint end slope of less than 1 sigma in this case, implying that the observed signature is moderately larger than one would expect from SB dimming alone, and indicating a true evolution in the faint end slope.

Day 1250

Monday.

1705.00013
Observational evidence of galaxy assembly bias
Montero-Dorta, et al

Analyze the spectra of 300,000 LRGs with stellar masses M*>1e11 Msun from SDSS-III BOSS survey.  By studying their SFHs, find 2 main evolutionary paths converging into the same quiescent galaxy population at z~0.55.  Fast-growing LRGs assemble 80% of their stellar mass very early on (z~5), whereas slow-growing LRGs reach the same evolutionary state at z~1.5.  Further investigation reveals that their clustering properties on scales of ~1-30 Mpc are, at a high level of significance, also different.  Fast-growing LRGs are found to be more strongly clustered and reside in overall denser LSS environments than slow-growing systems, for a given stellar-mass threshold.  Results imply a dependence of clustering on stellar-mass assembly history (naturally connected to the mass-formation history of the corresponding halos) for a homogeneous population of similar mass and color, which constitutes a strong observational evidence of galaxy assembly bias.