EMISSION-LINE OBJECTS NEAR QUASI-STELLAR OBJECT ABSORBERS .3. CLUSTERING AND COLORS OF MODERATE-REDSHIFT H-II REGIONS

Three deep narrow-band images of [O II] lambda-3727 at the redshift of known QSO absorption-line systems show evidence for enhanced star formation occurring in groups of giant H II regions spread over 100-300 h-1 kpc. The redshifts of the star formation are 0.6128, 0.633, and 1.328. Emission limits of 1 x 10(-17) ergs cm-2 s-1 make these candidates for the faintest known detections of optical emission from distant star-forming regions. The broad-band continuum colors of some of the emission-line candidate objects are typically blue in B-V color, although they simultaneously show a red V-R color, which suggests an unusual stellar population. Continuum magnitudes are 23-25 in the R band. We propose a model regarding the clustering of these star-forming objects and apply it to the question of large absorber cross sections and the mechanism of galaxy formation. In the model, the emission-line objects occur as bound groups of forming galaxy subunits. The typical inferred linear size of the groups at z = 0.6 is 800-1 kpc. The groups consist of 30-100 galaxy pieces each piece having continuum magnitude 23-26 in the R band, with each group having a velocity dispersion of less than 300 km s-1. Observations so far show 10 objects in a group with R < 25 spread over 300 h-1 kpc. The rate of star formation occurring in the group would be enough to generate a few times 10(10) M. stars in 1 Gyr, and given the small velocity dispersion, members of the group would merge through dynamical friction in a Hubble time.