GALAXIES CLUSTERING AROUND QSOS WITH Z=0.9-1.5 AND THE ORIGIN OF BLUE FIELD GALAXIES

Deep direct CCD observations in Mould-Cousins R and I passbands have been obtained for the fields of 16 radio-loud QSOs with 0.9 < z < 1.5. While we cannot confirm Tyson's report of excess galaxies with R < 21 lying within 30" of quasars in this redshift range, we do find a statistically significant excess of galaxies within 15" of the quasars and brighter than R = 23 and I = 22 (probability of chance occurrence P < 1%). Assuming the excess galaxies are indeed physically associated with the corresponding QSOs, these galaxies are roughly 0-3 mag brighter in R than first-ranked galaxies are predicted to be and are therefore several magnitudes overluminous (H0 = 50 km s-1 Mpc-1; q0 = 0.0). This possibility is not surprising in light of Yee and Green's tentative conclusion that galaxies in clusters associated with QSOs at redshifts near 0.6 are nearly 1 mag overluminous. Our data for one object, 1622 + 238 (z = 0.927), indicate that this quasar lies near the center of a rich, distant cluster of galaxies, but further observations are necessary to confirm the apparent association. Galaxy counts in the outer halves of our fields have been used to derive field galaxy counts as a function of magnitude to R = 23 and I = 22. After adjusting for the zero-point difference between Kron-Cousins R and Gunn r, our cumulative field galaxy densities agree within 7% with those derived by Yee and Green and by Sebok. The color-magnitude diagram for the field galaxies includes a large population (about 10%) of faint (R ≥ 22), very blue galaxies (R-I ≤ 0.2), presumably similar to the blue field galaxies reported in previous surveys at shorter wavelengths (e.g., Kron's and subsequent surveys). These objects are much bluer in R-I than Magellanic irregular galaxies at any redshift, and it has been suggested that they may be galaxies undergoing initial formation. We find that strong line emission almost certainly must be present in the R passband to produce the bluest colors observed. This population could be comprised of low-redshift, low-luminosity (H II region) galaxies of the type studied by French and/or higher redshift galaxies with strong cooling flows and [O II]. Spectroscopic confirmation of the strong line emission in these objects should be feasible, despite their faint apparent magnitudes.