HST OBSERVATIONS OF THE RADIO GALAXY MG-1136+1346 (Z=1.003)

We present images taken with the prerefurbishment Hubble Space Telesco pe of the z=1.003 radio galaxy MG 1136+1346 as part of a morphological study of the high-redshift radio-source population. The galaxy has a bright, unresolved nuclear component which contributes approximately h alf of the total light in the observed V (F555W) and I (F785LP) bands. We thus classify MG 1136+1346 as an N galaxy. Subtracting the nuclear component, we investigate the properties of the surrounding fuzz. The extended optical continuum consists of an elongated ''host galaxy'' w hich is aligned with the radio source, plus a compact (but extended) b lue nuclear region, which may be a central starburst or scattering reg ion. The large-scale emission in the I band can be modeled as an r(1/4 )-law profile with a scale length approximate to 33.5 kpc (H-0=50 km/s /Mpc; q(0)=0.1). However, there is significant asymmetric emission abo ve the simple r(1/4) law at large radii in both V and I bands. The col or of the large-scale continuum is substantially bluer than expected f or an early-type host galaxy at z=1, and is similar to the color of th e nuclear point source, as well as to the colors of other strongly ali gned 3CR radio galaxies at z approximate to 1. We consider the structu re and colors of the extended light in MG 1136+1346 in the context of models for the radio-optical alignment effect in radio galaxies. In or ientation-driven scenarios for AGN unification, it may be surprising t o find a good example of an aligned radio galaxy which nevertheless sh ows a strong, unresolved nucleus. The images also show several faint g alaxies near MG 1136+1346, including a very red companion at a project ed separation of 22.6 kpc from the radio galaxy. With I=24. 1 mag and (V-I)>2.9 mag, its properties are consistent with it being an early-ty pe companion galaxy at the redshift of the radio source. (C) 1996 Amer ican Astronomical Society.