The Galaxy-Halo/Subhalo connection: Mass relations and implications for some satellite occupational distributions

TL;DR

This paper derives stellar-to-halo/subhalo mass relations for central and satellite galaxies using observational data, revealing differences in these relations and their implications for satellite distributions.

Contribution

It provides new constraints on the mass relations and intrinsic scatter for central and satellite galaxies, and explores their implications for satellite occupation statistics.

Findings

Central galaxies are not typically within the mass range of the most massive satellites.

Probabilities of MW-sized halos hosting Magellanic-Clouds-sized satellites match observations.

The intrinsic scatter around mass relations is approximately 0.17 dex for both centrals and satellites.

Abstract

We infer the local stellar-to-halo/subhalo mass relations (MRs) for central and satellite galaxies separately. We constraint this relations by using several combinations of observational data, consisting of the total galaxy stellar mass function, its decomposition into centrals and satellites, and the projected two-point correlation functions measured in different stellar mass bins. The differences among the resulting MRs are within the model-fit uncertainties (which are very small, smaller than the intrinsic scatter between galaxy and halo mass), no matter what combination of data are used. We also constrain the values of the intrinsic scatter around the central-halo (CH) and satellite-subhalo (SS) MRs assuming them to be constant: sigma_c= 0.168+-0.051 dex and sigma_s = 0.172+-0.057 dex, respectively. The CH and SS MRs are actually different, in particular when we take the subhalo mass at the present-day epoch instead of at their accretion time. We calculate several population statistics. We find that the central galaxy is not on average within the mass distribution of the most-massive satellite, even for cluster-sized halos, i.e., centrals are not a mere realization of the high-end of the satellite mass function; however for > 3x10^13 msun halos, ~15% of centrals could be. We also find that the probabilities of MW-sized halos of having N Magellanic-Clouds (MCs)-sized satellites agree well with observational measures; for a halo mass of 2x10^12 msun, the probability to have 2 MCs is 5.4%, but if we exclude those systems with satellites larger than the MCs, then the probability decreases to <2.2%.