Journal Article

The <i>UV</i>–optical colour dependence of galaxy clustering in the local universe

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

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 407, issue 1, pages 55-70
Published in print September 2010 | ISSN: 0035-8711
Published online August 2010 | e-ISSN: 1365-2966 | DOI:
The UV–optical colour dependence of galaxy clustering in the local universe

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We measure the UV-optical colour dependence of galaxy clustering in the local Universe. Using the clean separation of the red and blue sequences made possible by the NUVr colour–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 ξ(rp, π) 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, ξ(rp, π) for all three samples show the effect of large-scale streaming from coherent infall. On scales of 1 h−1 Mpc < rp < 10 h−1 Mpc, the projected auto-correlation function wp(rp) for red and green galaxies fits a power law with slope γ∼ 1.93 and amplitude r0∼ 7.5 and 5.3, compared with γ∼ 1.75 and r0∼ 3.9 h−1 Mpc 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 wp(rp) for blue galaxies display an increase in convexity at ∼ 1 h−1 Mpc, with an excess of large-scale clustering. Our results suggest that the majority of blue galaxies are likely central galaxies in less massive haloes, 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 colour.

Keywords: methods: statistical; galaxies: clusters: general; galaxies: elliptical and lenticular; galaxies: evolution

Journal Article.  10748 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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