An Optical Near‐Infrared Study of Radio‐loud Quasar Environments. I. Methods and z = 1–2 Observations

We have conducted an optical/near-infrared study of the environments ofradio-loud quasars (RLQs) at redshifts z=0.6-2. In this paper we discuss thesample selection and observations for the z=1-2 subsample and the reduction andcataloguing techniques used. We discuss technical issues at some length, sincefew detailed descriptions of near-IR data reduction and multicolor objectcataloguing are currently available in single literature references. Our sample of 33 RLQs contains comparable numbers of flat- and steep- radiospectrum sources and sources of various radio morphologies, and spans a similarrange of absolute magnitude and radio power, allowing us to disentangledependence of environment on such properties from redshift evolution. We use the standard ``shift-and-stare'' method of creating deep mosaicedimages where the exposure time (and thus the RMS noise) at each pixel is notconstant across the mosaic. An unusual feature of our reduction procedure isthe creation of images with constant RMS noise from such mosaics. We adoptedthis procedure to enable use of the FOCAS detection package over almost theentire mosaic instead of only in the area of deepest observation where the RMSnoise is constant, thereby roughly doubling our areal coverage. We correct the object counts in our fields for stellar contamination usingthe SKY model of Cohen (1995) and compare the galaxy counts to those in randomfields. Even after accounting for possible systematic magnitude offsets we finda significant excess of K>=19 galaxies. Analysis and discussion of this excesspopulation is presented by Hall & Green (1998).