THE STELLAR-SUBHALO MASS RELATION OF SATELLITE GALAXIES

We extend the abundance matching technique (AMT) to infer the satellite-subhalo and central-halo mass relations (MRs) of local galaxies as well as the corresponding satellite conditional mass functions (CSMFs). We use as inputs the observed galaxy stellar mass function (GSMF) decomposed into centrals and satellites and the ACDM distinct halo and subhalo mass functions. We explore the effects of defining the subhalo mass, m(sub), at the time of (sub) halo accretion (m(sub)(acc)) versus defining it at the time of observation (m(sub)(obs)); we also test the standard assumption that centrals and satellites follow the same MRs. We show that this assumption leads to predictions in disagreement with observations, especially when m(sub)(obs) is used. We find that when the satellite-subhalo MRs are constrained by the satellite GSMF, they are always different from the central-halo MR: The smaller the stellar mass, the less massive the subhalo of satellites as compared to the halo of centrals of the same stellar mass. This difference is more dramatic when m(sub)(obs) is used instead of m(sub)(acc). On average, for stellar masses lower than similar to 2 x 10(11) M-circle dot, the dark mass of satellites decreased by 60%-65% with respect to their masses at accretion time. We find that MRs for both definitions of subhalo mass yield CSMFs in agreement with observations. Also, when these MRs are used in a halo occupation model, the predicted two-point correlation functions at different stellar mass bins agree with observations. The average stellar-halo MR is close to the MR of central galaxies alone, and conceptually this average MR is equivalent to abundance matching the cumulative total GSMF to the halo + subhalo mass function (the standard AMT). We show that the use of m(sub)(obs) leads to less uncertain MRs than m(sub)(acc) and discuss some implications of the obtained satellite-subhalo MR. For example, we show that the tension between abundance and dynamics of Milky Way satellites in the ACDM cosmogony gives a value of similar to-1.6 in the faint-end slope of the GSMF upturns.