Clustering properties of high redshift red galaxies in SA22 from the UKIDSS DXS

Deep, wide, near-infrared imaging surveys provide an opportunity to study the clustering of various galaxy populations at high redshift on the largest physical scales. We have selected $1<z<2$ extremely red objects (EROs) and $1<z<3$ distant red galaxies (DRGs) in SA22 from the near-infrared photometric data of the UKIDSS Deep eXtragalactic Survey (DXS) and $gri$ optical data from CTIO covering 3.3~deg$^2$. This is the largest contiguous area studied to sufficient depth to select these distant galaxies to date. The angular two-point correlation functions and the real space correlation lengths of each population are measured and show that both populations are strongly clustered and that the clustering cannot be parameterised with a single power law. The correlation function of EROs shows a double power law with the inflection at $sim$ 0.6$$--1.2$$ (0.6--1.2~h$^{-1}$~Mpc). The bright EROs ($K<18.8$) show stronger clustering on small scales but similar clustering on larger scales, whereas redder EROs show stronger clustering on all scales. Clustering differences between EROs that are old passively evolved galaxies (OGs) and dusty star-forming galaxies (DGs), on the basis of their $J-K$ colour, are also investigated. The clustering of $r-K$ EROs are compared with that of $i-K$ EROs and the differences are consistent with their expected redshift distributions. The correlation function of DRGs is also well described by a double power law and consistent with previous studies once the effects of the broader redshift distribution our selection of DRGs returns are taken into account. We also perform the same analysis on smaller sub-fields to investigate the impact of cosmic variance on the derived clustering properties. Currently this study is the most representative measurement of the clustering of massive galaxies at $z>1$ on large scales.

Luminous Red Galaxies in hierarchical cosmologies

Luminous red galaxies (LRGs) are much rarer and more massive than L* galaxies. Coupled with their extreme colours, LRGs therefore provide a demanding testing ground for the physics of massive galaxy formation. We present the first self-consistent predictions for the abundance and properties of LRGs in hierarchical structure formation models. We test two published models which use quite different mechanisms to suppress the formation of massive galaxies: the Bower et al. (2006) model, which invokes ``AGN-feedback to prevent gas from cooling in massive haloes, and the Baugh et al. (2005) model which relies upon a ``superwind to eject gas before it is turned into stars. Without adjusting any parameters, the Bower et al. model gives an excellent match to the observed luminosity function of LRGs in the SDSS (with a median redshift of z=0.24) and to their clustering; the Baugh et al. model is less successful in these respects. Both models fail to match the observed abundance of LRGs at z=0.5 to better than a factor of ~2. In the models, LRGs are typically bulge dominated systems with M* of ~2x10^11 h^{-1} M_sun and velocity dispersions of ~250 km s^{-1}. Around half of the stellar mass in the model LRGs is already formed by z~2.2 and is assembled into one main progenitor by z~1.5; on average, only 25% of the mass of the main progenitor is added after z~1. LRGs are predicted to be found in a wide range of halo masses, a conclusion which relies on properly taking into account the scatter in the formation histories of haloes. Remarkably, we find that the correlation function of LRGs is predicted to be a power law down to small pair separations, in excellent agreement with observational estimates. Neither the Bower et al. nor the Baugh et al. model is able to reproduce the observed radii of LRGs.