Journal Article

The clustering and abundance of star-forming and passive galaxies at <i>z</i>∼ 2

W. G. Hartley, K. P. Lane, O. Almaini, M. Cirasuolo, S. Foucaud, C. Simpson, S. Maddox, I. Smail, C. J. Conselice, R. J. McLure and J. S. Dunlop

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 391, issue 3, pages 1301-1307
Published in print December 2008 | ISSN: 0035-8711
Published online November 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13956.x
The clustering and abundance of star-forming and passive galaxies at z∼ 2

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We use the UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Ultra-deep survey (UDS), currently the deepest panoramic near-infrared survey, together with deep Subaru optical imaging to measure the clustering, number counts and luminosity function of galaxies at z∼ 2 selected using the BzK selection technique. We find that both star-forming (sBzK) and passive (pBzK) galaxies, to a magnitude limit of KAB < 23, are strongly clustered. The passive galaxies are the most strongly clustered population, with scalelengths of r0= 15.0+1.9−2.2 h−1Mpc compared with r0= 6.75+0.34−0.37 h−1Mpc for star-forming galaxies. The direct implication is that passive galaxies inhabit the most massive dark matter haloes, and are thus identified as the progenitors of the most massive galaxies at the present day. In addition, the pBzKs exhibit a sharp flattening and potential turnover in their number counts, in agreement with other recent studies. This plateau cannot be explained by the effects of incompleteness. We conclude that only very massive galaxies are undergoing passive evolution at this early epoch, consistent with the downsizing scenario for galaxy evolution. Assuming a purely passive evolution for the pBzKs from their median redshift to the present day, their luminosity function suggests that only ∼2.5 per cent of present-day massive ellipticals had a pBzK as a main progenitor.

Keywords: galaxies: evolution; galaxies: formation; galaxies: high-redshift; large-scale structure of Universe; infrared: galaxies

Journal Article.  5389 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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