The Stellar-Subhalo Mass Relation of Satellite Galaxies

Abstract

We extend the abundance matching technique (AMT) to infer the satellite-subhalo and centralhalo mass relations (MRs) of local galaxies, as well as the corresponding satellite conditional mass functions. We use the observed galaxy stellar mass function (GSMF) decomposed into centrals and satellites and the Λ-CDM distinct halo and subhalo mass functions as inputs. We explore the effects of defining the subhalo mass, m sub , at the time of (sub)halo accretion (m acc sub ) versus defining it at the time of observation (m obs sub ); and we test the standard assumption that centrals and satellites follow the same MRs. We show that this assumption leads to predictions in disagreement with observations, specially when m obs sub is used. Instead, 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 is the subhalo of satellites as compared to the halo of centrals of the same stellar mass. This difference is more dramatic when m obs sub is used instead of m acc sub . On average, for stellar masses lower than ∼ 2 × 10 11 M ⊙ , 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 satellite conditional mass functions (CSMF) 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 obs sub leads to less uncertain MRs than m acc sub , 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 Λ-CDM cosmogony gives if the faint-end slope of the GSMF upturns to a value of ∼ −1.6.

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“…While recent studies (e.g., Rodríguez-Puebla et al 2012 show some indication that satellite galaxies tend to have slightly more stellar mass than central galaxies with the same halo mass, these results depend on the subhalo mass definition used; in particular, the luminosity-mass relation for satellites and central galaxies has been found to be not very different when the mass of the subhalo is defined at the time of accretion (as done in this paper). -A very simple functional form (see Blain et al 2003, and reference therein) is assumed for galaxy SEDs:…”

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“…As cosmological simulations such as Millennium Boylan-Kolchin et al 2009) and Bolshoi (Klypin, Trujillo-Gomez & Primack 2011) resolved dark matter halos increasingly well, it has been a major goal to use such simulations to improve our understanding of the connection between halos and the galaxies that they host. Abundance matching (Kravtsov et al 2004;Vale & Ostriker 2004) -which in its most basic form is just rank ordering galaxies by their stellar mass and assigning them to halos ranked by mass or peak circular velocity -leads to predictions of the galaxy autocorrelation functions for both ⋆ arodr104@ucsc.edu bright and faint galaxies that are in excellent agreement with observations (e.g., Conroy, Wechsler & Kravtsov 2006;Klypin, Trujillo-Gomez & Primack 2011;Rodríguez-Puebla, Drory & Avila-Reese 2012;Reddick et al 2013, and references therein). Abundance matching taking into account galaxy star formation rates also allows calculation of the typical relationship between the mass of dark matter halos and the stellar mass of the hosted galaxies (e.g.…”

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