SHAM beyond clustering: new tests of galaxy–halo abundance matching with galaxy groups

Abstract

We construct mock catalogs of galaxy groups using subhalo abundance matching\n(SHAM) and undertake several new tests of the SHAM prescription for the\ngalaxy-dark matter connection. All SHAM models we studied exhibit significant\ntension with galaxy groups observed in the Sloan Digital Sky Survey (SDSS). The\nSHAM prediction for the field galaxy luminosity function (LF) is systematically\ntoo dim, and the group galaxy LF systematically too bright, regardless of the\ndetails of the SHAM prescription. SHAM models connecting r-band luminosity, Mr,\nto Vacc, the maximum circular velocity of a subhalo at the time of accretion\nonto the host, faithfully reproduce galaxy group abundance as a function of\nrichness, g(N). However, SHAM models connecting Mr with Vpeak, the peak value\nof Vmax over the entire merger history of the halo, over-predict galaxy group\nabundance. Our results suggest that no SHAM model can simultaneously reproduce\nthe observed g(N) and two-point projected galaxy clustering. Nevertheless, we\nalso report a new success of SHAM: an accurate prediction for Phi(m12), the\nabundance of galaxy groups as a function of magnitude gap m12, defined as the\ndifference between the r-band absolute magnitude of the two brightest group\nmembers. We show that it may be possible to use joint measurements of g(N) and\nPhi(m12) to tightly constrain the details of the SHAM implementation.\nAdditionally, we show that the hypothesis that the luminosity gap is\nconstructed via random draws from a universal LF provides a poor description of\nthe data, contradicting recent claims in the literature. Finally, we test a\ncommon assumption of the Conditional Luminosity Function (CLF) formalism, that\nthe satellite LF need only be conditioned by the brightness of the central\ngalaxy. We find this assumption to be well-supported by the observed Phi(m12).\n