The Clustering of Extragalactic Extremely Red Objects

We have measured the angular and spatial clustering of 671 K < 18.40, R - K > 5 extremely red objects (EROs) from a 0.98 deg2 subregion of the NOAO Deep Wide-Field Survey (NDWFS). Our study covers nearly 5 times the area and has twice the sample size of any previous ERO clustering study. The wide field of view and BWRIK passbands of the NDWFS allow us to place improved constraints on the clustering of z ~ 1 EROs. We find that the angular clustering of EROs is slightly weaker than in previous measurements, and ω(1′) = 0.25 ± 0.05 for K < 18.40 EROs. We find no significant correlation of ERO spatial clustering with redshift, apparent color, or absolute magnitude, although given the uncertainties, such correlations remain plausible. We find that the spatial clustering of K < 18.40, R - K > 5 EROs is well approximated by a power law, with r0 = 9.7 ± 1.1 h-1 Mpc in comoving coordinates. This is comparable to the clustering of ~4L* early-type galaxies at z < 1 and is consistent with the brightest EROs being the progenitors of the most massive elliptical galaxies. There is evidence of the angular clustering of EROs decreasing with increasing apparent magnitude, when NDWFS measurements of ERO clustering are combined with those from the literature. Unless the redshift distribution of K ≳ 20 EROs is very broad, the spatial clustering of EROs decreases from r0 = 9.7 ± 1.1 h-1 Mpc for K < 18.40 to r0 ~ 7.5 h-1 Mpc for K ≳ 20 EROs.