Lyman Limit Imaging of High Redshift Galaxies. III. New Observations of 4 QSO Fields

Abstract

We present the results of deep Lyman limit imaging in four new fields as part of a continuing search for galaxies at $3.0 \le z \le 3.5$. The technique uses a custom broad--band filter set ($U_n G {\cal R}$) designed to isolate objects having Lyman continuum breaks superposed on otherwise flat--spectrum ultraviolet continua. The observations are specifically aimed at detecting known galaxies producing optically thick QSO metal line absorption systems, but are equally sensitive to more generally distributed objects at the redshifts of interest. Together with previously published results of the survey, we have now detected in two out of six cases objects with the expected properties of star--forming galaxies at $z \simgt 3$ within 3~arcsec of the QSO sight lines; the two candidate absorbers have similar luminosities, $M_B \simeq -22$ ($q_0=0.5$, $H_0=50$ \kms Mpc$^{-1}$), and impact parameters, $R \sim 10~h^{-1}$~kpc. The average surface density of robust Lyman break objects is $\sim 0.5$ galaxies per square arcminute to a magnitude limit ${\cal R} = 25.0$. A simple, ``no evolution'' model based on the properties of normal galaxies at $z \simlt 1$ predicts a density of Lyman break objects only a few times larger than observed. We conclude that there is a substantial population of star--forming galaxies, of relatively normal luminosity, already in place at $z = 3 - 3.5$.