The Extremely Red Host Galaxy of GRB 080207

Abstract

We present optical, near-infrared, and Spitzer IRAC and MIPS observations of the host galaxy of the dark Swift gamma-ray burst GRB 080207. The host is faint, with extremely red optical-infrared colors (R - K = 6.3, 24 μm/R-band flux ~1000) making it an extremely red object (ERO) and a dust-obscured galaxy (DOG). The spectral energy distribution (SED) shows the clear signature of the 1.6 μm photometric "bump," typical of evolved stellar populations. We use this bump to establish the photometric redshift z _phot as 2.2^+0.2 _{- 0.3}, using a vast library of SED templates, including M 82. The star formation rate (SFR) inferred from the SED fitting is ~119 M _sun yr^-1, the stellar mass 3 × 10¹¹ M _sun, and A_V extinction from 1 to 2 mag. The ERO and DOG nature of the host galaxy of the dark GRB 080207 may be emblematic of a distinct class of dark GRB hosts, with high SFRs, evolved and metal-rich stellar populations, and significant dust extinction within the host galaxy.