Properties of Candidate Cluster Galaxies at z=1--2

Original · EN

I discuss the properties of a population of candidate cluster galaxies recently identified in the fields of radio-loud quasars at z=1--2. The magnitude, spatial, and color distributions of the excess galaxies in these fields are consistent with the quasars residing in moderately rich galaxy overdensities dominated by early-type galaxies. The broadband SEDs of very red galaxies in several fields suggest that there is considerable dispersion in the properties of early-type galaxies in these clusters at z 1.5. Most excess galaxies are best fit as 2--3 Gyr old ellipticals, but some are either 4--5 Gyr old or considerably more metal-rich, and others must be extremely dusty. The latter are part of a ``J-band dropout'' population which includes a number of galaxies in one field which are probably at z 2.5, background to the quasar. Finally, I discuss narrowband redshifted H-alpha imaging in two fields which has yielded at least one detection. At z>1.3 cluster galaxy star formation rates can be measured from H-alpha in the near-IR, rest-frame 1500-Angstrom light in the optical, and eventually rest-frame far-IR emission using SCUBA, to help determine the star formation histories of cluster galaxies as function of redshift.