The Nature of the Small Galaxies in the Hubble Deep Field

Abstract

We present results from a study of very small galaxies (isophotal area ≤ 0.2°”) with photometric redshifts 1 ≤ z ≤ 4.5 detected in the region of the northern Hubble Deep Field covered by NICMOS observations at 1.6 and 1.1 microns. We estimate that ~50 percent of these sources are star-forming galaxies at redshifts 2 < z < 3.5 and ~45 percent at are 3.5 < z < 4.5, with the remaining 5% at 1 < z < 2. We have examined averaged images of these faint (V_(606) ~ 27-29), compact objects to search for extended, surrounding flux from older, fainter populations of stars. We find no evidence that the small objects in the Hubble Deep Field are embedded in fainter, more extended galaxies. The majority are indeed isolated and compact. We estimate the 5σ depth of the averaged images to be H_(160) ≈29.8 AB magnitudes per square arcsecond.