Host Galaxy Properties of the Subluminous GRB 120422A/SN 2012bz
  GRB 120422A is a nearby (z = 0.283) long-duration GRB (LGRB) detected by
Swift with E(gamma,iso) ~ 4.5\times1049 erg. It is also associated with the
spectroscopically-confirmed broad-lined Type Ic SN 2012bz. These properties
establish GRB 120422A/SN 2012bz as the sixth and newest member of the class of
subluminous GRB/SNe. Observations also show that GRB 120422A/SN 2012bz occurred
at an unusually large offset (~8 kpc) from the host galaxy nucleus, setting it
apart from other nearby LGRBs and leading to speculation that the host
environment may have undergone prior interaction activity. Here we present
spectroscopic observations using the 6.5m Magellan telescope at Las Campanas.
We extract spectra at three specific locations within the GRB/SN host galaxy,
including the host nucleus, the explosion site, and the "bridge" of diffuse
emission connecting these two regions. We measure a metallicity of log(O/H) +
12 = 8.3 +/- 0.1 and a star formation rate per unit area of 0.08 Mo/yr/kpc^2 at
the host nucleus. At the GRB/SN explosion site we measure a comparable
metallicity of log(O/H) + 12 = 8.2 +/- 0.1, but find a much lower star
formation rate per unit area of 0.01 M/yr/kpc^2. We also compare the host
galaxy of this event to the hosts other LGRBs, including samples of subluminous
LGRBs and cosmological LGRBs, and find no systematic metallicity difference
between the environments of these different subtypes.
