A Deep Multicolor Survey. VII. Extremely Red Objects and Galaxy Formation

Extremely Red Objects (EROs) offer a window to the universe at z~1 analogousto that provided by the Lyman Break galaxies at z=3. Passive evolution andhierarchical galaxy formation models make very distinct predictions for the K(2.2um) surface density of galaxies at z~1 and EROs are a powerful constrainton these theories. I present a study of nine resolved EROs with R-K>5.3 andK<18 mag found in the 185 arcmin^2 of the Deep Multicolor Survey withnear-infrared imaging. Photometric redshifts for these galaxies shows they alllie at z=0.8-1.3. The relatively blue J-K colors of these galaxies suggest thatmost are old ellipticals, rather than dusty starbursts. The surface density ofEROs in this survey (>0.05 arcmin^-2), which is a lower limit to the total z~1galaxy surface density, is an order of magnitude below the prediction ofpassive galaxy evolution, yet over a factor of two higher than the hierarchicalgalaxy formation prediction for a flat, matter-dominated universe. A flat,Lambda-dominated universe may bring the hierarchical galaxy formation modelinto agreement with the observed ERO surface density.Comment: AJ Accepted (May 2001). 16 pages with 2 embedded figure