The Masses, Ancestors, and Descendants of Extremely Red Objects: Constraints from Spatial Clustering

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Abstract
Wide-field near-infrared (IR) surveys have revealed a population of galaxies with very red optical-IR colors, which have been termed "extremely red objects" (EROs). Modeling suggests that such red colors (R-K > 5) could be produced by galaxies at z 1 with either very old stellar populations or very high dust extinction. Recently, it has been discovered that EROs are strongly clustered. Are these objects the high-redshift progenitors of present-day giant ellipticals (gEs)? Are they already massive at this epoch? Are they the descendants of the z ~ 3 Lyman break galaxies (LBGs), which have also been identified as possible high-redshift progenitors of gEs? We address these questions within the framework of the cold dark matter paradigm, using an analytic model that connects the number density and clustering, or bias, of an observed population with the halo occupation function (the number of observed galaxies per halo of a given mass). We find that EROs reside in massive dark matter halos, with average mass > 1013 h M☉. The occupation function that we derive for EROs is very similar to the one we derive for z = 0, L > L*, early-type galaxies, whereas the occupation function for LBGs is skewed toward much smaller host halo masses ( ≈ 1011-1012 h M☉). We then use the derived occupation function parameters to explore the possible evolutionary connections between these three populations.

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