Morphologies and Spectral Energy Distributions of Extremely Red Galaxies in the GOODS-South Field

Using U'- through Ks-band imaging data in the GOODS-South field, we construct a large, complete sample of 275 ``extremely red objects'' (EROs; Kₛ3. 35; AB), all with deep HST/ACS imaging in B₄35, V₆06, i₇75, and z₈50, and well-calibrated photometric redshifts. Quantitative concentration and asymmetry measurements fail to separate EROs into distinct morphological classes. We therefore visually classify the morphologies of all EROs into four broad types: ``Early'' (elliptical-like), ``Late'' (disk galaxies), ``Irregular'' and ``Other'' (chain galaxies and low surface brightness galaxies), and calculate their relative fractions and comoving space densities. For a broad range of limiting magnitudes and color thresholds, the relative number of early-type EROs is approximately constant at 33-44%, and the comoving space densities of Early- and Late-type EROs are comparable. Mean rest-frame spectral energy distributions (SEDs) at wavelengths between 0. 1 and 1. 2 um are constructed for all EROs. The SEDs are extremely similar in their range of shapes, independent of morphological type. The implication is that any differences between the broad-band SEDs of Early-type EROs and the other types are relatively subtle, and there is no robust way of photometrically distinguishing between different morphological types with usual optical/near-infrared photometry.