A Revised Estimate of the CO (J=1-0) Emission from the Host Galaxy of GRB 030329 Using the Nobeyama Millimeter Array
Abstract
A sensitive observation of the CO (J=1-0) molecular line emission in the host galaxy of GRB 030329 (z =0.1685) has been performed using the Nobeyama Millimeter Array in order to detect molecular gas and hidden star formation. No sign of CO emission was detected, which invalidates our previous report on the presence of molecular gas. The 3sigma upperlimit on the CO line luminosity (L'CO) of the host galaxy is 6.9 x 108 K km s-1 pc2. The lowerlimit of the host galaxy's metallicity is estimated to be 12+log(O/H) ~ 7.9, which yields a CO line luminosity to H2 conversion factor of alphaCO = 40 Msun (K km s-1 pc2)-1. Assuming this alphaCO factor, the 3sigma upperlimit on the molecular gas mass of the host galaxy is 2.8 x 1010 Msun. Based on the Schmidt law, the 3sigma upperlimit of the total star formation rate (SFR) of the host galaxy is estimated to be 38 Msun yr-1. These results independently confirm the inferences of previous observations in the optical, submillimeter, and X-ray band, which regard this host galaxy as a compact dwarf galaxy, and not a massive, aggressively star forming galaxy.
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