We measure the angular clustering of 33 415 extremely red objects (EROs) in the Elais-N1 field covering 5.33 deg$^{2}$, which cover the redshift range $z=0.8$ to $2$. This sample was made by merging the UKIDSS Deep eXtragalactic Survey (DXS) with the
optical Subaru and Pan-STARRS PS1 datasets. We confirm the existence of a clear break in the angular correlation function at $sim 0.02^{circ}$ corresponding to $1 h^{-1}$ Mpc at $zsim1$. We find that redder or brighter EROs are more clustered than bluer or fainter ones. Halo Occupation Distribution (HOD) model fits imply that the average mass of dark matter haloes which host EROs is over $10^{13} h^{-1} M_{odot}$ and that EROs have a bias ranging from 2.7 to 3.5. Compared to EROs at $zsim1.1$, at $zsim1.5$ EROs have a higher bias and fewer are expected to be satellite galaxies. Furthermore, EROs reside in similar dark matter haloes to those that host $10^{11.0} M_{odot}<M_{*}<10^{11.5} M_{odot}$ galaxies. We compare our new measurement and HOD fits with the predictions of the GALFORM semi-analytical galaxy formation model. Overall, the clustering predicted by GALFORM gives an encouraging match to our results. However, compared to our deductions from the measurements, GALFORM puts EROs into lower mass haloes and predicts that a larger fraction of EROs are satellite galaxies. This suggests that the treatment of gas cooling may need to be revised in the model. Our analysis illustrates the potential of clustering analyses to provide observational constraints on theoretical models of galaxy formation.
We present a comprehensive study of 250,000 galaxies targeted by the Baryon Oscillation Spectroscopic Survey (BOSS) up to z ~ 0.7 with the specific goal of identifying and characterising a population of galaxies that has evolved without significant m
erging. We compute a likelihood that each BOSS galaxy is a progenitor of the Luminous Red Galaxies (LRGs) sample, targeted by SDSS-I/II up z ~ 0.5, by using the fossil record of LRGs and their inferred star-formation histories, metallicity histories and dust content. We determine merger rates, luminosity growth rates and the evolution of the large-scale clustering between the two surveys, and we investigate the effect of using different stellar population synthesis models in our conclusions. We demonstrate that our sample is slowly evolving (of the order of 2 +/- 1.5% per Gyr by merging). Our conclusions refer to the bright and massive end of the galaxy population, with Mi0.55 < -22, and M* > 1E11.2 Msolar, corresponding roughly to 95% and 40% of the LRGs and BOSS galaxy populations, respectively. Our analysis further shows that any possible excess of flux in BOSS galaxies, when compared to LRGs, from potentially unresolved targets at z ~ 0.55 must be less than 1% in the r0.55-band (approximately equivalent to the g-band in the rest-frame of galaxies at z=0.55). When weighting the BOSS galaxies based on the predicted properties of the LRGs, and restricting the analysis to the reddest BOSS galaxies, we find an evolution of the large-scale clustering that is consistent with dynamical passive evolution, assuming a standard cosmology. We conclude that our likelihoods give a weighted sample that is as clean and as close to passive evolution (in dynamical terms, i.e. no or negligible merging) as possible, and that is optimal for cosmological studies.
We study the projected radial distribution of satellite galaxies around more than 28,000 Luminous Red Galaxies (LRGs) at 0.28<z<0.40 and trace the gravitational potential of LRG groups in the range 15<r/kpc<700. We show that at large radii the satell
ite number density profile is well fitted by a projected NFW profile with r_s~270 kpc and that at small radii this model underestimates the number of satellite galaxies. Utilizing the previously measured stellar light distribution of LRGs from deep imaging stacks we demonstrate that this small scale excess is consistent with a non-negligible baryonic mass contribution to the gravitational potential of massive groups and clusters. The combined NFW+scaled stellar profile provides an excellent fit to the satellite number density profile all the way from 15 kpc to 700 kpc. Dark matter dominates the total mass profile of LRG halos at r>25 kpc whereas baryons account for more than 50% of the mass at smaller radii. We calculate the total dark-to-baryonic mass ratio and show that it is consistent with measurements from weak lensing for environments dominated by massive early type galaxies. Finally, we divide the satellite galaxies in our sample into three luminosity bins and show that the satellite light profiles of all brightness levels are consistent with each other outside of roughly 25 kpc. At smaller radii we find evidence for a mild mass segregation with an increasing fraction of bright satellites close to the central LRG.
We present a statistical study of the luminosity functions of galaxies surrounding luminous red galaxies (LRGs) at average redshifts <z>=0.34 and <z>=0.65. The luminosity functions are derived by extracting source photometry around more than 40,000 L
RGs and subtracting foreground and background contamination using randomly selected control fields. We show that at both studied redshifts the average luminosity functions of the LRGs and their satellite galaxies are poorly fitted by a Schechter function due to a luminosity gap between the centrals and their most luminous satellites. We utilize a two-component fit of a Schechter function plus a log-normal distribution to demonstrate that LRGs are typically brighter than their most luminous satellite by roughly 1.3 magnitudes. This luminosity gap implies that interactions within LRG environments are typically restricted to minor mergers with mass ratios of 1:4 or lower. The luminosity functions further imply that roughly 35% of the mass in the environment is locked in the LRG itself, supporting the idea that mass growth through major mergers within the environment is unlikely. Lastly, we show that the luminosity gap may be at least partially explained by the selection of LRGs as the gap can be reproduced by sparsely sampling a Schechter function. In that case LRGs may represent only a small fraction of central galaxies in similar mass halos.
