We present a machine-learning (ML) approach for estimating galaxycluster masses from Chandra mock images. We utilize a ConvolutionalNeural Network (CNN), a deep ML tool commonly used in image recognitiontasks. The CNN is trained and tested on our sample of 7896 Chandra X-raymock observations, which are based on 329 massive clusters from the{\text{}}{IllustrisTNG} simulation. Our CNN learns from a low resolutionspatial distribution of photon counts and does not use spectralinformation. Despite our simplifying assumption to neglect spectralinformation, the resulting mass values estimated by the CNN exhibitsmall bias in comparison to the true masses of the simulated clusters(-0.02 dex) and reproduce the cluster masses with low intrinsic scatter,

The combination of galaxy-galaxy lensing (GGL) with galaxy clustering isone of the most promising routes to determining the amplitude of matterclustering at low redshifts. We show that extending clustering+GGLanalyses from the linear regime down to {̃ } 0.5 h^{-1} Mpc scalesincreases their constraining power considerably, even aftermarginalizing over a flexible model of non-linear galaxy bias. Using agrid of cosmological N-body simulations, we construct a Taylor-expansionemulator that predicts the galaxy autocorrelation ξ_gg(r) andgalaxy-matter cross-correlation ξ_gm(r) as a function ofσ₈, Ω_m, and halo occupation distribution (HOD)parameters, which are allowed to vary with large-scale environment torepresent possible effects of galaxy assembly bias. We present forecastsfor a fiducial case that corresponds to BOSS LOWZ galaxy clustering andSDSS-depth weak lensing (effective source density ̃0.3arcmin^-2). Using tangential shear and projected correlationfunction measurements over 0.5 ≤ r_ p ≤ 30 h^{-1} Mpc yields a 2 percent constraint on the parameter combination σ _8Ω _ m^{0.6}, a factorof two better than a constraint that excludes non-linear scales (r_ p> 2 h^{-1} Mpc, 4 h^{-1} Mpc for γ_t, w_p). Muchof this improvement comes from the non-linear clustering information,which breaks degeneracies among HOD parameters. Increasing the effectivesource density to 3 arcmin^-2 sharpens the constraint on σ _8Ω_ m^{0.6} by a further factor of two. With robust modelling into thenon-linear regime, low-redshift measurements of matter clustering at the1-per cent level with clustering+GGL alone are well within reach ofcurrent data sets such as those provided by the Dark Energy Survey.

We present configuration-space estimators for the auto- and cross-covariance of two- and three-point correlation functions (2PCF and 3PCF)in general survey geometries. These are derived in the Gaussian limit(setting higher order correlation functions to zero), but for arbitrarynon-linear 2PCFs (which may be estimated from the survey itself), with ashot-noise rescaling parameter included to capture non-Gaussianity. Wegeneralize previous approaches to include Legendre moments via ageometry-correction function calibrated from measured pair and triplecounts. Making use of importance sampling and random particlecatalogues, we can estimate model covariances in fractions of the timerequired to do so with mocks, obtaining estimates with negligiblesampling noise in ̃10 (̃100) CPU-hours for the 2PCF (3PCF)autocovariance. We compare results to sample covariances from a suite ofBOSS DR12 mocks and find the matrices to be in good agreement, assuminga shot-noise rescaling parameter of 1.03 (1.20) for the 2PCF (3PCF). Toobtain strongest constraints on cosmological parameters, we must usemultiple statistics in concert; having robust methods to measure theircovariances at low computational cost is thus of great relevance toupcoming surveys.

Although photometric redshifts (photo-z's) are crucial ingredients forcurrent and upcoming large-scale surveys, the high-quality spectroscopicredshifts currently available to train, validate, and test them aresubstantially non-representative in both magnitude and colour. Weinvestigate the nature and structure of this bias by tracking howobjects from a heterogeneous training sample contribute to photo-zpredictions as a function of magnitude and colour, and illustrate thatthe underlying redshift distribution at fixed colour can evolve stronglyas a function of magnitude. We then test the robustness of the galaxy-galaxy lensing signal in 120 deg² of HSC-SSP DR1 data tospectroscopic completeness and photo-z biases, and find that theirimpacts are sub-dominant to current statistical uncertainties. Ourmethodology provides a framework to investigate how spectroscopicincompleteness can impact photo-z-based weak lensing predictions infuture surveys such as LSST and WFIRST.

We present a method for generating suites of dark matter halo catalogueswith only a few N-body simulations, focusing on making small changes tothe underlying cosmology of a simulation with high precision. In thecontext of blind challenges, this allows us to re-use a simulation bygiving it a new cosmology after the original cosmology is revealed.Starting with full N-body realizations of an original cosmology and atarget cosmology, we fit a transfer function that displaces haloes inthe original so that the galaxy/HOD power spectrum matches that of thetarget cosmology. This measured transfer function can then be applied toa new realization of the original cosmology to create a new realizationof the target cosmology. For a 1 per cent change in σ₈, weachieve 0.1 per cent accuracy to k = 1 h Mpc^{-1} in the real-spacepower spectrum; this degrades to 0.3 per cent when the transfer functionis applied to a new realization. We achieve similar accuracy in theredshift-space monopole and quadrupole. In all cases, the result isbetter than the sample variance of our 1.1 h^{-1} Gpc simulation boxes.

We present a high-fidelity realization of the cosmological N-bodysimulation from the Schneider et al. code comparison project. Thesimulation was performed with our ABACUSN-body code, which offers high-force accuracy, high performance, and minimal particle integrationerrors. The simulation consists of 2048³ particles in a 500h^{-1} Mpc box for a particle mass of 1.2× 10^9 h^{-1} M_\odot with 10h^{-1} kpc spline softening. ABACUS executed 1052 global time-steps to z= 0 in 107 h on one dual-Xeon, dual-GPU node, for a mean rate of 23million particles per second per step. We find ABACUS is in goodagreement with RAMSES and PKDGRAV3 and less so with GADGET3. We validateour choice of time-step by halving the step size and find sub-percentdifferences in the power spectrum and 2PCF at nearly all measuredscales, with {\lt }0.3{{ per cent}} errors at k\lt 10 Mpc^{-1} h. Onlarge scales, ABACUS reproduces linear theory better than 0.01 per cent.Simulation snapshots are available athttp://nbody.rc.fas.harvard.edu/public/S2016.

Covariance matrix estimation is a persistent challenge for cosmology. Wefocus on a class of model covariance matrices that can be generated withhigh accuracy and precision, using a tiny fraction of the computationalresources that would be required to achieve comparably precisecovariance matrices using mock catalogues. In previous work, the freeparameters in these models were determined using sample covariancematrices computed using a large number of mocks, but we demonstrate thatthose parameters can be estimated consistently and with good precisionby applying jackknife methods to a single survey volume. This enablesmodel covariance matrices that are calibrated from data alone, with noreference to mocks.

The DESI Legacy Imaging Surveys (http://legacysurvey.org/) are acombination of three public projects (the Dark Energy Camera LegacySurvey, the Beijing-Arizona Sky Survey, and the Mayall z-band LegacySurvey) that will jointly image ≈14,000 deg² of theextragalactic sky visible from the northern hemisphere in three opticalbands (g, r, and z) using telescopes at the Kitt Peak NationalObservatory and the Cerro Tololo Inter-American Observatory. Thecombined survey footprint is split into two contiguous areas by theGalactic plane. The optical imaging is conducted using a unique strategyof dynamically adjusting the exposure times and pointing selectionduring observing that results in a survey of nearly uniform depth. Inaddition to calibrated images, the project is delivering a catalog,constructed by using a probabilistic inference-based approach toestimate source shapes and brightnesses. The catalog includes photometryfrom the grz optical bands and from four mid-infrared bands (at 3.4,4.6, 12, and 22 μm) observed by the Wide-field Infrared Survey Explorersatellite during its full operational lifetime. The project plans twopublic data releases each year. All the software used to generate thecatalogs is also released with the data. This paper provides an overviewof the Legacy Surveys project.

We use the IllustrisTNG (TNG) simulations to explore the galaxy-haloconnection as inferred from state-of-the-art cosmological,magnetohydrodynamical simulations. With the high-mass resolution andlarge volume achieved by combining the 100 Mpc (TNG100) and 300 Mpc(TNG300) volumes, we establish the mean occupancy of central andsatellite galaxies and their dependence on the properties of the darkmatter haloes hosting them. We derive best-fitting HOD parameters fromTNG100 and TNG300 for target galaxy number densities of \bar{n}_g =0.032 and \bar{n}_g = 0.016 h^3 Mpc^-3, respectively,corresponding to a minimum galaxy stellar mass of M_\star ̃ 1.9× 10^9and M_\star ̃ 3.5× 10^9 M_☉, respectively, in hosts more massive than10^{11} M_☉. Consistent with previous work, we find that haloes locatedin dense environments, with low concentrations, later formation times,and high angular momenta are richest in their satellite population. Atlow mass, highly concentrated haloes and those located in overdenseregions are more likely to contain a central galaxy. The degree ofenvironmental dependence is sensitive to the definition adopted for thephysical boundary of the host halo. We examine the extent to whichcorrelations between galaxy occupancy and halo properties areindependent and demonstrate that HODs predicted by halo mass andpresent-day concentration capture the qualitative dependence on theremaining halo properties. At fixed halo mass, concentration is a strongpredictor of the stellar mass of the central galaxy, which may play adefining role in the fate of the satellite population. The radialdistribution of satellite galaxies, which exhibits a universal formacross a wide range of host halo mass, is described accurately by thebest-fitting NFW density profile of their host haloes.

In preparation for deep extragalactic imaging with the James Webb SpaceTelescope, we explore the clustering of massive halos at z = 8 and 10using a large N-body simulation. We find that halos with masses of10⁹-10¹¹ h ^-1 M _☉, which arethose expected to host galaxies detectable with JWST, are highlyclustered with bias factors ranging from 5 to 30 depending strongly onmass, as well as on redshift and scale. This results in correlationlengths of 5-10 h ^-1 Mpc, similar to those of today’sgalaxies. Our results are based on a simulation of 130 billion particlesin a box of size 250 h ^-1 Mpc using our new high-accuracyABACUS simulation code, the corrections to cosmological initialconditions of Garrison et al., and the Planck 2015 cosmology. We usevariations between sub-volumes to estimate the detectability of theclustering. Because of the very strong interhalo clustering, we findthat a medium-sized survey with a transverse size of the order of 25 h^-1 comoving Mpc (about 13′) may be able to detect theclustering of z = 8-10 galaxies with only 500-1000 survey objects if thegalaxies indeed occupy the most massive dark matter halos.

We utilize mock catalogues from high-accuracy cosmological N-bodysimulations to quantify shifts in the recovery of the acoustic scalethat could potentially result from galaxy clustering bias. Therelationship between galaxies and dark matter haloes presents acomplicated source of systematic errors in modern redshift surveys,particularly when aiming to make cosmological measurements to sub-percent precision. Apart from a scalar, linear bias parameter accountingfor the density contrast ratio between matter tracers and the truematter distribution, other types of galaxy bias, such as assembly andvelocity biases, may also significantly alter clustering signals fromsmall to large scales. We create mocks based on generalized halooccupation populations of 36 periodic boxes from the ABACUSCOSMOSrelease, and test various biased models along with an unbiasedbase case in a total volume of 48 h^{-3} Gpc³. Tworeconstruction methods are applied to galaxy samples and the apparentacoustic scale is derived by fitting the two-point correlation functionmultipoles. With respect to the baseline, we find a 0.3 per cent shiftin the line-of-sight acoustic scale for one variation in the satellitegalaxy population, and we find a 0.7 per cent shift for an extreme levelof velocity bias of the central galaxies. All other bias models areconsistent with zero shift at the 0.2 per cent level afterreconstruction. We note that the bias models explored are relativelylarge variations, producing sizeable and likely distinguishable changesin small-scale clustering, the modelling of which would furthercalibrate the baryon acoustic oscillations standard ruler.

We present a public data release of halo catalogs from a suite of 125cosmological N-body simulations from the ABACUS project. The simulationsspan 40 wCDM cosmologies centered on the Planck 2015 cosmology at twomass resolutions, 4 × 10¹⁰ h ^-1 M_⊙ and 1 × 10¹⁰ h ^-1 M_⊙, in 1.1 h ^-1 Gpc and 720 h^-1 Mpc boxes, respectively. The boxes are phase-matchedto suppress sample variance and isolate cosmology dependence. Additionalvolume is available via 16 boxes of fixed cosmology and varied phase; afew boxes of single-parameter excursions from Planck 2015 are alsoprovided. Catalogs spanning z = 1.5 to 0.1 are available forfriends-of-friends and ROCKSTAR halo finders and include particlesubsamples. All data products are available at https://lgarrison.github.io/AbacusCosmos.

We develop a formalism for measuring the cosmological distance scalefrom baryon acoustic oscillations (BAO) using the cross-correlation of asparse redshift survey with a denser photometric sample. This reducesthe shot noise that would otherwise affect the autocorrelation of thesparse spectroscopic map. As a proof of principle, we make the firston-sky application of this method to a sparse sample defined as the z> 0.6 tail of the Sloan Digital Sky Survey's (SDSS) BOSS/CMASS sampleof galaxies and a dense photometric sample from SDSS DR9. We find a2.8σ preference for the BAO peak in the cross-correlation at aneffective z = 0.64, from which we measure the angular diameter distanceD_M(z = 0.64) = (2418 ± 73 Mpc)(r_s/r_s,fid). Accordingly, we expect that using this method to combinesparse spectroscopy with the deep, high-quality imaging that is just nowbecoming available will enable higher precision BAO measurements thanpossible with the spectroscopy alone.

We investigate the potential sources of theoretical systematics in theanisotropic Baryon Acoustic Oscillation (BAO) distance scalemeasurements from the clustering of galaxies in configuration spaceusing the final Data Release (DR12) of the Baryon OscillationSpectroscopic Survey (BOSS). We perform a detailed study of the impacton BAO measurements from choices in the methodology such as fiducialcosmology, clustering estimators, random catalogues, fitting templates,and covariance matrices. The theoretical systematic uncertainties in BAOparameters are found to be 0.002 in the isotropic dilation α and0.003 in the quadrupolar dilation ɛ. The leading source ofsystematic uncertainty is related to the reconstruction techniques.Theoretical uncertainties are sub-dominant compared with the statisticaluncertainties for BOSS survey, accounting 0.2σ_stat forα and 0.25σ_stat for ɛ(σ_{α, stat} ˜ 0.010 andσ_{ɛ, stat} ˜ 0.012, respectively). We alsopresent BAO-only distance scale constraints from the anisotropicanalysis of the correlation function. Our constraints on the angulardiameter distance D_A(z) and the Hubble parameter H(z),including both statistical and theoretical systematic uncertainties, are1.5 per cent and 2.8 per cent at z_eff = 0.38, 1.4 per centand 2.4 per cent at z_eff = 0.51, and 1.7 per cent and 2.6 percent at z_eff = 0.61. This paper is part of a set thatanalyses the final galaxy clustering data set from BOSS. Themeasurements and likelihoods presented here are cross-checked with otherBAO analysis in Alam et al. The systematic error budget concerning themethodology on post-reconstruction BAO analysis presented here is usedin Alam et al. to produce the final cosmological constraints from BOSS.

We present measurements of the Baryon Acoustic Oscillation (BAO) scalein redshift-space using the clustering of quasars. We consider a sampleof 147 000 quasars from the extended Baryon Oscillation SpectroscopicSurvey (eBOSS) distributed over 2044 square degrees with redshifts 0.8< z < 2.2 and measure their spherically averaged clustering inboth configuration and Fourier space. Our observational data set and the1400 simulated realizations of the data set allow us to detect apreference for BAO that is greater than 2.8σ. We determine thespherically averaged BAO distance to z = 1.52 to 3.8 per cent precision:D_V(z = 1.52) = 3843 ± 147(r_d/r_d,fid)Mpc. This is the first time the location of the BAO featurehas been measured between redshifts 1 and 2. Our result is fullyconsistent with the prediction obtained by extrapolating the Planck flatΛCDM best-fitting cosmology. All of our results are consistentwith basic large-scale structure (LSS) theory, confirming quasars to bea reliable tracer of LSS, and provide a starting point for numerouscosmological tests to be performed with eBOSS quasar samples. We combineour result with previous, independent, BAO distance measurements toconstruct an updated BAO distance-ladder. Using these BAO data alone andmarginalizing over the length of the standard ruler, we findΩ_Λ > 0 at 6.6σ significance whentesting a ΛCDM model with free curvature.

We search for a galaxy clustering bias due to a modulation of galaxynumber with the baryon-dark matter relative velocity resulting fromrecombination-era physics. We find no detected signal and place theconstraint b_v < 0.01 on the relative velocity bias for theCMASS galaxies. This bias is an important potential systematic of baryonacoustic oscillation (BAO) method measurements of the cosmic distancescale using the two-point clustering. Our limit on the relative velocitybias indicates a systematic shift of no more than 0.3 per cent rms inthe distance scale inferred from the BAO feature in the BOSS two-pointclustering, well below the 1 per cent statistical error of thismeasurement. This constraint is the most stringent currently availableand has important implications for the ability of upcoming large-scalestructure surveys such as the Dark Energy Spectroscopic Instrument(DESI) to self-protect against the relative velocity as a possiblesystematic.

We present the GeneRalized ANd Differentiable Halo OccupationDistribution (GRAND-HOD) routine that generalizes the standard fiveparameter halo occupation distribution (HOD) model with varioushalo-scale physics and assembly bias. We describe the methodology offour different generalizations: satellite distribution generalization,velocity bias, closest approach distance generalization, and assemblybias. We showcase the signatures of these generalizations in the 2-pointcorrelation function (2PCF) and the squeezed 3-point correlationfunction (squeezed 3PCF). We identify generalized HOD prescriptions thatare nearly degenerate in the projected 2PCF and demonstrate that thesedegeneracies are broken in the redshift-space anisotropic 2PCF and thesqueezed 3PCF. We also discuss the possibility of identifyingdegeneracies in the anisotropic 2PCF and further demonstrate the extraconstraining power of the squeezed 3PCF on galaxy-halo connectionmodels. We find that within our current HOD framework, the anisotropic2PCF can predict the squeezed 3PCF better than its statistical error.This implies that a discordant squeezed 3PCF measurement could falsifythe particular HOD model space. Alternatively, it is possible thatfurther generalizations of the HOD model would open opportunities forthe squeezed 3PCF to provide novel parameter measurements. The GRAND-HODPYTHON package is publicly available athttps://github.com/SandyYuan/GRAND-HOD.

The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has beenin operation since 2014 July. This paper describes the second datarelease from this phase, and the 14th from SDSS overall (making thisData Release Fourteen or DR14). This release makes the data taken bySDSS-IV in its first two years of operation (2014-2016 July)public. Like all previous SDSS releases, DR14 is cumulative, includingthe most recent reductions and calibrations of all data taken by SDSSsince the first phase began operations in 2000. New in DR14 is the firstpublic release of data from the extended Baryon OscillationSpectroscopic Survey; the first data from the second phase of the ApachePoint Observatory (APO) Galactic Evolution Experiment (APOGEE-2),including stellar parameter estimates from an innovative data-drivenmachine-learning algorithm known as “The Cannon” and almosttwice as many data cubes from the Mapping Nearby Galaxies at APO (MaNGA)survey as were in the previous release (N = 2812 in total). This paperdescribes the location and format of the publicly available data fromthe SDSS-IV surveys. We provide references to the important technicalpapers describing how these data have been taken (both targeting andobservation details) and processed for scientific use. The SDSS web site(www.sdss.org) has been updated forthis release and provides links to data downloads, as well as tutorialsand examples of data use. SDSS-IV is planning to continue to collectastronomical data until 2020 and will be followed by SDSS-V.

We present an iterative method to reconstruct the linear-theory initialconditions from the late-time cosmological matter density field, withthe intent of improving the recovery of the cosmic distance scale fromthe baryon acoustic oscillations. We present tests using the dark matterdensity field in both real and redshift space generated from an N-bodysimulation. In redshift space at z = 0.5, we find that the reconstructeddisplacement field using our iterative method are more than 80 per centcorrelated with the true displacement field of the dark matter particleson scales k < 0.10 h Mpc^-1. Furthermore, we show that thetwo-point correlation function of our reconstructed density fieldmatches that of the initial density field substantially better,especially on small scales (<40 h^-1 Mpc). Ourredshift-space results are improved if we use an anisotropic smoothingso as to account for the reduced small-scale information along the lineof sight in redshift space.

We present an original phenomenological model to describe the evolutionof galaxy number counts, morphologies, and spectral energy distributionsacross a wide range of redshifts (0.2< z< 15) and stellar masses[{log}(M/{M}_⊙ )≥slant 6]. Our model follows observedmass and luminosity functions of both star-forming and quiescentgalaxies, and reproduces the redshift evolution of colors, sizes, starformation, and chemical properties of the observed galaxy population.Unlike other existing approaches, our model includes a self-consistenttreatment of stellar and photoionized gas emission and dust attenuationbased on the BEAGLE tool. The mock galaxy catalogs generated with ournew model can be used to simulate and optimize extragalactic surveyswith future facilities such as the James Webb Space Telescope (JWST),and to enable critical assessments of analysis procedures,interpretation tools, and measurement systematics for both photometricand spectroscopic data. As a first application of this work, we makepredictions for the upcoming JWST Advanced Deep Extragalactic Survey(JADES), a joint program of the JWST/NIRCam and NIRSpec Guaranteed TimeObservations teams. We show that JADES will detect, with NIRCam imaging,1000s of galaxies at z ≳ 6, and 10s at z ≳ 10 at{m}_{AB}≲ 30 (5σ) within the 236 arcmin²of the survey. The JADES data will enable accurate constraints on theevolution of the UV luminosity function at z > 8, and resolve thecurrent debate about the rate of evolution of galaxies at z ≳ 8.Ready-to-use mock catalogs and software to generate new realizations arepublicly available as the JAdes extraGalactic Ultradeep ArtificialRealizations (JAGUAR) package.