Global analysis of luminosity- and colour-dependent galaxy clustering in the Sloan Digital Sky Survey

Abstract

We present a Halo Occupation Distribution (HOD) analysis of the luminosity-and colour-dependent galaxy clustering in the Sloan Digital Sky Survey. A novelty of our technique is that it uses a combination of clustering measurements in luminosity bins to perform a global likelihood analysis, simultaneously constraining the HOD parameters for a range of luminosity thresholds. We present simple, smooth fitting functions which accurately describe the resulting luminosity dependence of the best-fit HOD parameters. To minimise systematic halo modelling effects, we use theoretical halo 2-point correlation functions directly measured and tabulated from a suite of N -body simulations spanning a large enough dynamic range in halo mass and spatial separation. Thus, our modelling correctly accounts for non-linear and scale-dependent halo bias as well as any departure of halo profiles from universality, and we additionally account for halo exclusion using the hard sphere approximation. Using colour-dependent clustering information, we constrain the satellite galaxy red fraction in a model-independent manner which does not rely on any group-finding algorithm. We find that the resulting luminosity dependence of the satellite red fraction is significantly shallower than corresponding measurements from galaxy group catalogues, and we provide a simple fitting function to describe this dependence. Our fitting functions are readily usable in generating low-redshift mock galaxy catalogues, and we discuss some potentially interesting applications as well as possible extensions of our technique.

The distribution of HI velocity profiles in a $Λ$CDM universe

“…the mass distribution of Hi in the disk (e.g., Schulman et al 1994, see section 3.1). Our analysis applied this calculation to the rotation curves of Hi-bearing central galaxies having optical magnitude Mr ≤ −19 in a statistically realistic mock catalog of galaxies in a (300h −1 Mpc) 3 box (Paranjape et al 2021, hereafter, PCS21) constructed using an optical+Hi halo occupation distribution (HOD) model (Paul et al 2018(Paul et al , 2019, see section 2). The HOD is constrained to reproduce the abundances and luminosity-and colour-dependent clustering of optically selected galaxies in SDSS, as well as the abundances and Hi-dependent clustering of massive Hi-selected galaxies in the ALFALFA survey.…”

“…Mock central and satellite galaxies were populated in these host haloes using the PCS21 algorithm to produce a luminosity-complete sample of galaxies with an r-band absolute magnitude threshold Mr ≤ −19. This algorithm is based on the halo occupation distribution (HOD) model and optical-Hi scaling relation calibrated by Paul et al (2018) and Paul et al (2019), and additionally assigns each mock galaxy with realistic values of g − r and u − r colours and stellar mass m * . Most importantly for the present work, approximately 60% of these galaxies are also assigned values of neutral hydrogen (Hi) mass mHi sampled from the optical-Hi scaling relation.…”

The external field effect in cold dark matter models

“…Since the halo concentration cannot be reliably measured for haloes with fewer than about ∼ 400 particles, we use the method presented by Ramakrishnan et al (2021) to assign concentrations cvir (assuming Navarro et al 1996, NFW profiles) conditioned on the mass and local tidal environment of individual haloes. 2 The galaxies were populated using a halo occupation distribution (HOD) model and Hi-optical scaling relations calibrated by Paul et al (2018) and Paul et al (2019) using luminosity-and colour-dependent clustering measurements from the Sloan Digital Sky Survey (SDSS, York et al 2000;Zehavi et al 2011) and Hi-dependent clustering measurements from the Arecibo Legacy Fast ALFA survey (ALFALFA, Giovanelli et al 2005;Guo et al 2017). Each galaxy in the mock is assigned absolute magnitudes in SDSS u, g and r bands (with a threshold Mr ≤ −19 imposed by the SDSS clustering measurements) and a stellar mass m * using a colour-dependent mass-to-light ratio.…”

The radial acceleration relation in a $Λ$CDM universe

“…The PCS21 algorithm, which is based on the halo occupation distribution (HOD) models calibrated by Paul et al (2018) and Paul et al (2019), populates host halos in this box with mock central and satellite galaxies, producing a luminosity-complete sample of galaxies with an r-band absolute magnitude threshold Mr ≤ −19. In addition to the r-band magnitude, each mock galaxy is assigned realistic values of g − r and u − r colours and stellar mass m * .…”