A Molecular gas rich GRB host galaxy at the peak of cosmic star
  formation
  We report the detection of the CO(3-2) emission line from the host galaxy of
Gamma Ray Burst (GRB) 080207 at $z$ = 2.086. This is the first detection of
molecular gas in emission from a GRB host galaxy beyond redshift 1. We find
this galaxy to be rich in molecular gas with a mass of $1.1 \times 10^{11}\,\rm
M_{\odot}$ assuming $\alpha_{\rm CO}=$ 4.36 $\rm M_{\odot}(\rm
K\,km\,s^{-1}\,pc^2)^{-1}$. The molecular gas mass fraction of the galaxy is
$\sim$ 0.5, typical of star forming galaxies (SFGs) with similar stellar masses
and redshifts. With a $\rm SFR_{FIR}$ of 260 $\rm M_{\odot}\,yr^{-1}$, we
measure a molecular-gas-depletion timescale of 0.43 Gyr, near the peak of the
depletion timescale distribution of SFGs at similar redshifts. Our findings are
therefore in contradiction with the proposed molecular gas deficiency in GRB
host galaxies. We argue that the reported molecular gas deficiency for GRB
hosts could be the artifact of improper comparisons or neglecting the effect of
the typical low metallicities of GRB hosts on the CO-to-molecular-gas
conversion factor. We also compare the kinematics of the CO(3-2) emission line
to that of the H$\alpha$ emission line from the host galaxy. We find the
H$\alpha$ emission to have contributions from two separate components, a narrow
and a broad one. The narrow component matches the CO emission well in velocity
space. The broad component, with a FWHM of $\sim$ 1100 $\rm km\,s^{-1}$, is
separated by $+390$ $\rm km\,s^{-1}$ in velocity space from the narrow
component. We speculate this broad component to be associated with a powerful
outflow in the host galaxy or in an interacting system.
