Galaxy and Mass Assembly (GAMA): Small-scale anisotropic galaxy clustering and the pairwise velocity dispersion of galaxies

TL;DR

This study measures the small-scale galaxy pairwise velocity dispersion in the GAMA survey, revealing a luminosity-dependent increase, and finds that current models overestimate PVD for faint galaxies due to halo occupation assumptions.

Contribution

It provides the first detailed measurement of PVD at small scales in the GAMA survey and compares these results with semi-analytic models, highlighting discrepancies in faint galaxy predictions.

Findings

PVD increases with galaxy luminosity at small scales.

GAMA survey enables reliable PVD measurements down to 0.01 Mpc/h.

Models over-predict PVD for faint galaxies due to halo occupation issues.

Abstract

The galaxy pairwise velocity dispersion (PVD) can provide important tests of non-standard gravity and galaxy formation models. We describe measurements of the PVD of galaxies in the Galaxy and Mass Assembly (GAMA) survey as a function of projected separation and galaxy luminosity. Due to the faint magnitude limit ($r < 19.8$) and highly-complete spectroscopic sampling of the GAMA survey, we are able to reliably measure the PVD to smaller scales ($r_\bot = 0.01$ Mpc/h) than previous work. The measured PVD at projected separations $r_\bot <~ 1$ Mpc/h increases near-monotonically with increasing luminosity from $\sigma \approx 200$ km/s at $M_r = -17$ mag to $\sigma \approx 600$ km/s at $M_r \approx -22$ mag. Analysis of the Gonzalez-Perez (2014) GALFORM semi-analytic model yields no such trend of PVD with luminosity: the model over-predicts the PVD for faint galaxies. This is most likely a result of the model placing too many low-luminosity galaxies in massive halos.