The UV-optical colour dependence of galaxy clustering in the local universe

Y S Loh ,Samir Salim,Patrick Morrissey,Karl Forster,R Michael Rich,Mark Seibert,D Christopher Martin,Susan G Neff,Young-Wook Lee,Ryan P Mallery,Barry F Madore,Barry Y Welsh,Ryan Scranton,Timothy M Heckman,Luciana Bianchi,David Schiminovich,Tom A Barlow,Peter G Friedman,Ted K Wyder ,J Donas ,S Heinis ,B Milliard ,S Arnouts ,Alexander S Szalay

doi:10.1111/j.1365-2966.2010.16908.x

Abstract

We measure the UV-optical color dependence of galaxy clustering in the local universe. Using the clean separation of the red and blue sequences made possible by the NUV - r color-magnitude diagram, we segregate the galaxies into red, blue and intermediate "green" classes. We explore the clustering as a function of this segregation by removing the dependence on luminosity and by excluding edge-on galaxies as a means of a non-model dependent veto of highly extincted galaxies. We find that \xi (r_p, \pi) for both red and green galaxies shows strong redshift space distortion on small scales -- the "finger-of-God" effect, with green galaxies having a lower amplitude than is seen for the red sequence, and the blue sequence showing almost no distortion. On large scales, \xi (r_p, \pi) for all three samples show the effect of large-scale streaming from coherent infall. On scales 1 Mpc/h < r_p < 10 Mpc/h, the projected auto-correlation function w_p(r_p) for red and green galaxies fits a power-law with slope \gamma ~ 1.93 and amplitude r_0 ~ 7.5 and 5.3, compared with \gamma ~ 1.75 and r_0 ~ 3.9 Mpc/h for blue sequence galaxies. Compared to the clustering of a fiducial L* galaxy, the red, green, and blue have a relative bias of 1.5, 1.1, and 0.9 respectively. The w_p(r_p) for blue galaxies display an increase in convexity at ~ 1 Mpc/h, with an excess of large scale clustering. Our results suggest that the majority of blue galaxies are likely central galaxies in less massive halos, while red and green galaxies have larger satellite fractions, and preferentially reside in virialized structures. If blue sequence galaxies migrate to the red sequence via processes like mergers or quenching that take them through the green valley, such a transformation may be accompanied by a change in environment in addition to any change in luminosity and color.

Highlights

With the advent of the Sloan Digital Sky Survey (SDSS; York et al 2000) and its value-added galaxy catalogues, it has been possible to study the subject of galaxy bimodality and its relationship to fundamental properties, such as stellar mass and star formation history (e.g. Kauffmann et al 2003; Schiminovich et al 2007; Salim et al 2007)
Our results suggest that on scales typical of dark matter haloes, galaxies drawn from the green and blue populations are less associated than would be predicted by their respective auto-correlation function (ACF)
It is noteworthy that the slope of the blue correlation function begins shallowing at r ∼ 1 h−1 Mpc, displaying the kind of one- and two-halo segregation expected from a correlation function dominated by central galaxies

Summary

Introduction

With the advent of the Sloan Digital Sky Survey (SDSS; York et al 2000) and its value-added galaxy catalogues, it has been possible to study the subject of galaxy bimodality and its relationship to fundamental properties, such as stellar mass and star formation history (e.g. Kauffmann et al 2003; Schiminovich et al 2007; Salim et al 2007). In a plot of optical g − r colour versus Mr, red galaxies define a clear sequence, while the locus of blue galaxies is broadened into the socalled blue cloud. Between the blue and red sequences there are galaxies present in a so-called green valley. Many of these are spectroscopically classified Type II active galactic nuclei (AGN) (Rich et al 2005; Martin et al 2007; Salim et al 2007)

Methods

Discussion

Conclusion