An optical near-infrared study of radio-loud quasar environments. I. Methods and z = 1-2 observations.
HALL P.B., GREEN R.F. and COHEN M.
Abstract (from CDS):
We have conducted an optical/near-infrared study of the environments of radio-loud quasars (RLQs) at redshifts z = 0.6-2.0. In this paper we discuss the sample selection and observations for the z = 1.0-2.0 subsample and the reduction and cataloging techniques used. We discuss technical issues at some length, since few detailed descriptions of near-IR data reduction and multicolor object cataloging are currently available in single literature references. Our sample of 33 RLQs contains comparable numbers of flat and steep radio spectrum sources and sources of various radio morphologies and spans a similar range of Mabs and Prad, which allows us to disentangle dependence of environment on optical or radio luminosity from redshift evolution. We use the standard ``shift-and-stare'' method of creating deep mosaicked images in which the exposure time (and thus the rms noise) at each pixel is not constant across the mosaic. An unusual feature of our reduction procedure is the creation of images with constant rms noise from such mosaics. We adopted this procedure to enable use of the FOCAS detection package over almost the entire mosaic instead of only in the area of deepest observation where the rms noise is constant, thereby roughly doubling our areal coverage. We correct the object counts in our fields for stellar contamination using the SKY model of Cohen and compare the galaxy counts to those in random fields. Even after accounting for possible systematic magnitude offsets, we find a significant excess of K ≳ 19 galaxies. Analysis and discussion of this excess population is presented by Hall & Green.
Galaxies: Clusters: General - Galaxies: Quasars: General - Radio Continuum: Galaxies - Surveys