We report here a factor of 5.7 higher total CO flux in Arp 244 ( the “ Antennae ” galaxies ) than that previously accepted in the literature ( thus a total molecular gas mass of 1.5 \times 10 ^ { 10 } M _ { \odot } ) , based on our fully sampled CO ( 1-0 ) observations at the NRAO 12m telescope .
Currently , much of the understanding and modeling of the star formation in Arp 244 has been derived from a much lower molecular gas mass .
It is imperative to reconsider all as the high molecular gas mass might provide sufficient fuel for ultraluminous extreme starburst in Arp 244 once the merging advances to late stage .

Our observations show that the molecular gas peaks predominately in the disk-disk overlap region between the nuclei , similar to the far-infrared ( FIR ) and mid-infrared ( MIR ) emission .
The bulk of the molecular gas is forming into stars with a normal star formation efficiency ( SFE ) L _ { IR } / M ( { H } _ { 2 } ) \approx 4.2 \hbox { L$ { } _ { \odot } $ } / \hbox { M$ { } _ { \odot } $ } , same as that of giant molecular clouds in the Galactic disk .
Additional supportive evidence is the extremely low fraction of the dense molecular gas in Arp 244 , revealed by our detections of the HCN ( 1-0 ) emission , which traces the active star-forming gas at density \lower 2.0 pt \hbox { $ \buildrel > \over { \sim } $ } 10 ^ { 4 } cm ^ { -3 } .

Using the high-resolution BIMA plus the NRAO 12m telescope , full-synthesis CO ( 1-0 ) images , and our VLA continuum maps at 20cm , we estimate the local SFE indicated by the ratio map of the radio continuum to CO ( 1-0 ) emission , down to kpc scale .
Remarkably , the local SFE stays roughly same over the bulk of the molecular gas distribution .
Only some localized regions show the highest radio-to-CO ratios that we have identified as the sites of the most intense starbursts with SFE \lower 2.0 pt \hbox { $ \buildrel > \over { \sim } $ } 20 ~ { } \hbox { L$ { } _ { \odot } $ } / \hbox { M$ { } % _ { \odot } $ } .
Here we have assumed that the 20cm emission is a fairly good indicator of star formation down to kpc scale in Arp 244 because of the well-known correlation between the FIR and the radio continuum emission .
These starburst regions are confined exclusively in the dusty patches seen in the HST optical images near the CO and FIR peaks where presumably the violent starbursts are heavily obscured .
Nevertheless , recent large-scale star formation is going on throughout the system ( e.g. , concentrations of numerous super-star clusters and MIR “ hotspots ” ) , yet the measured level is more suggestive of a moderate starburst ( SFE \lower 2.0 pt \hbox { $ \buildrel > \over { \sim } $ } 10 ~ { } \hbox { L$ { } _ { \odot } $ } / \hbox { M$ { } % _ { \odot } $ } ) or a weak to normal star formation ( SFE \sim 4 ~ { } \hbox { L$ { } _ { \odot } $ } / \hbox { M$ { } _ { \odot } $ } ) , not necessarily occurring at the high concentrations of the molecular gas reservoir .
The overall starburst from the bulk of the molecular gas is yet to be initiated as most of the gas further condenses into kpc scale in the final coalescence .