HST Observations of the Radio Galaxy MG 1136+1346 (z=1.003)

Abstract

We present images taken with the prerefurbishment Hubble Space Telescope 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 half 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" which is aligned with the radio source, plus a compact (but extended) blue nuclear region, which may be a central starburst or scattering region. The large-scale emission in the I band can be modeled as an r^1/4^ law profile with a scale length ~33.5 kpc (H_0_ = 50 km/-s/Mpc; q_0_ = 0.1). However, there is significant asymmetric emission above the simple r^1/4^ law at large radii in both V and I bands. The color of the large-scale continuum is substantially bluer than expected for an early-type host galaxy at z = I, and is similar to the color of the nuclear point source, as well as to the colors of other strongly aligned 3CR radio galaxies at z ~ 1. We consider the structure 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 orientation-driven scenarios for AGN unification, it may be surprising to find a good example of an aligned radio galaxy which nevertheless shows a strong, unresolved nucleus. The images also show several faint galaxies near MG 1136+1346, including a very red companion at a projected 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-type companion galaxy at the redshift of the radio source.