The Circular Velocity Function of Group Galaxies

Abstract

A robust prediction of $\Lambda \mathrm{CDM}$ cosmology is the halo circular velocity function (CVF), a dynamical cousin of the halo mass function. The correspondence between theoretical and observed CVFs is uncertain, however: cluster galaxies are reported to exhibit a power-law CVF consistent with $N$-body simulations, but that of the field is distinctly Schechter-like, flattened relative to $\Lambda \mathrm{CDM}$ expectations at circular velocities $v_c\lesssim 200\mathrm{km}{\mathrm{s}}^{-1}$. Groups offer a powerful probe of the role environment plays in this discrepancy as they bridge the field and clusters. Here, we construct the CVF for a large, mass- and multiplicity-complete sample of group galaxies from the Sloan Digital Sky Survey. Using independent photometric $v_c$ estimators, we find no transition from a field- to $\Lambda \mathrm{CDM}$-shaped CVF above $v_c=50\mathrm{km}{\mathrm{s}}^{-1}$ as a function of group halo mass. All groups with $12.4\lesssim \log M_{\mathrm{halo}}/M_{\odot }\lesssim 15.1$ (Local Group analogs to rich clusters) display similar Schechter-like CVFs marginally suppressed at low-$v_c$ compared to that of the field. Conversely, some agreement with $N$-body results emerges for samples saturated with late-type galaxies, with isolated late-types displaying a CVF similar in shape to $\Lambda \mathrm{CDM}$ predictions. We conclude that the flattening of the low-$v_c$ slope in groups is due to their depressed late-type fractions -- environment affecting the CVF only to the extent that it correlates with this quantity -- and that previous cluster analyses may suffer from interloper contamination. These results serve as useful benchmarks for cosmological simulations of galaxy formation.

16 pages, 16 figures; Accepted to ApJ August 2014. ArXiv version updated to reflect changes made during refereeing; results unchanged

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Cited by in corpus (4)

• How to Reconcile the Observed Velocity Function of Galaxies with Theory
• The Califa and Hipass velocity function for all morphological galaxy types
• Constraining the Milky Way's Ultraviolet to Infrared SED with Gaussian Process Regression
• The circular velocity and halo mass functions of galaxies in the nearby Universe