NATURE OF COMPACT GALAXIES IN THE HUBBLE DEEP FIELD .1. GLOBAL PROPERTIES

We present 10 m Keck spectroscopy and photometry for a sample of 61 sm all (r(1/2) less than or equal to 0''.5), faint (I-814 less than or eq ual to 23.74), high-surface brightness (mu(I814) < 22.2 mag arcsec(-2) ) galaxies in fields flanking the Hubble Deep Field. The majority of t his empirically defined sample of compact galaxies lies at redshifts 0 .4 less than or similar to z less than or similar to 1 (88% completene ss in redshift identifications), ruling out a large component of low-r edshift galaxies. The number of such galaxies in the range 1.4 less th an or similar to z less than or similar to 2.2 is also constrained to less than or similar to 10%. The majority of the observed galaxies are emission-line systems, while a significant fraction (23%-34%) appear to be normal ellipticals or otherwise early-type systems. One object i s an active galactic nucleus, and two are at high redshift (z > 2). Th e Keck redshift and photometric data are combined with Hubble Space Te lescope images to derive luminosities and physical sizes. We also use emission-line widths, where available, to estimate masses. About two-t hirds of the emission-line galaxies, or roughly one-half the sample, a re small, low-mass, relatively luminous systems with properties resemb ling those of local H II galaxies. We compare the properties and numbe rs of these galaxies to the ''bursting dwarf'' model of Babul & Fergus on. Our sample includes many galaxies similar to the model galaxies in the redshift range 0.4 less than or similar to z less than or similar to 0.7, but the majority of our compact galaxies are more luminous (b y up to an order of magnitude) than those of the model. The number of galaxies fitting the model parameters are lower by a factor of 2-3 tha n predicted. An examination of samples used in analyses of disk surfac e brightness at redshifts z > 0.5 shows that compact galaxies are like ly to contribute to the strong disk luminosity evolution found in some studies. Estimates of comoving volume densities indicate that the pop ulation of apparent H II galaxies evolves rapidly from redshifts of z similar to 1 to the present. It appears that not all of these galaxies can be progenitors of present-day spheroidal galaxies, although the n umbers of them with sizes and masses comparable to spheroidals is not dissimilar to estimates of the local field spheroidal density. We also present 51 additional redshifts, acquired for other projects during t he same observing period, for a total of 105 objects with identified r edshifts z < 2 in the Hubble Deep Field and its flanking fields.