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 3 \sigma upperlimit on the CO line luminosity ( L \arcmin _ { \mathrm { CO } } ) of the host galaxy is 6.9 \times 10 ^ { 8 } \mathrm { K km s ^ { -1 } pc ^ { 2 } } .
The lowerlimit of the host galaxy ’ s metallicity is estimated to be 12 + \log ( \mathrm { O / H } ) \sim 7.9 , which yields a CO line luminosity to \mathrm { H _ { 2 } } conversion factor of \alpha _ { \mathrm { CO } } = 40 M _ { \mathrm { \sun } } ( \mathrm { K km s ^ { -1 } pc ^ { 2 } } ) ^ { % -1 } .
Assuming this \alpha _ { \mathrm { CO } } factor , the 3 \sigma upperlimit on the molecular gas mass of the host galaxy is 2.8 \times 10 ^ { 10 } M _ { \mathrm { \sun } } .
Based on the Schmidt law , the 3 \sigma upperlimit of the total star formation rate ( SFR ) of the host galaxy is estimated to be 38 M _ { \mathrm { \sun } } \mathrm { 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 .