Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2010-12-06
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
Accepted for publication in ApJ. Correction made to typo in halo masses in conclusions
Scientific paper
We present an analysis of the clustering of galaxies as a function of their stellar mass at 1 < z < 2 using data from the NEWFIRM Medium Band Survey (NMBS). The precise photometric redshifts and stellar masses that the NMBS produces allows us to define a series of mass limited samples of galaxies more massive than 0.7, 1 and 3x10^10 Msun in redshift intervals centered on z = 1.1, 1.5 and 1.9 respectively. In each redshift interval we show that there exists a strong dependence of clustering strength on the stellar mass limit of the sample, with more massive galaxies showing a higher clustering amplitude on all scales. We further interpret our clustering measurements in the LCDM cosmological context using the halo model of galaxy clustering. We show that the typical halo mass of central and satellite galaxies increases with stellar mass, whereas the satellite fraction decreases with stellar mass, qualitatively the same as is seen at z < 1. We see little evidence of any redshift dependence in the stellar mass-to-halo mass relationship over our narrow redshift range. However, when we compare with similar measurements at z~0, we see clear evidence for a change in this relation. If we assume a universal baryon fraction, the ratio of stellar mass to halo mass reveals the fraction of baryons that have been converted to stars. We see that the peak in this star formation efficiency for central galaxies shifts to higher halo masses at higher redshift, moving from ~7x10^11 Msun at z~0 to ~3x10^12 Msun at z~1.5, revealing evidence of `halo downsizing'. Finally we show that for highly biased galaxy populations at z > 1 there may be a discrepancy between the measured space density and clustering and that predicted by the halo model. This could imply that there is a problem with one or more ingredients of the halo model at these redshifts, for instance the halo bias relation or the halo profile.
Brammer Gabriel
Franx Marijn
Kriek Mariska
Labb'e Ivo
Lundgren Britt F.
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