We report the detection of ongoing star formation in the prominent tidal arms near NGC 3077 ( member of the M 81 triplet ) .
In total , 36 faint compact H ii regions were identified , covering an area of \sim 4 \times 6 kpc ^ { 2 } .
Most of the H ii regions are found at H i column densities above 1 \times 10 ^ { 21 } cm ^ { -2 } ( on scales of 200 pc ) , well within the range of threshold columns measured in normal galaxies .
The H ii luminosity function resembles the ones derived for other low–mass dwarf galaxies in the same group ; we derive a total star formation rate of 2.6 \times 10 ^ { -3 } M _ { \odot } yr ^ { -1 } in the tidal feature .
We also present new high–resolution imaging of the molecular gas distribution in the tidal arm using CO observations obtained with the OVRO interferometer .
We recover about one sixth of the CO flux ( or M _ { H 2 } \sim 2 \times 10 ^ { 6 } M _ { \odot } , assuming a Galactic conversion factor ) originally detected in the IRAM 30 m single dish observations , indicating the presence of a diffuse molecular gas component in the tidal arm .
The brightest CO peak in the interferometer map ( comprising half of the detected CO flux ) is coincident with one of the brightest H ii regions in the feature .
Assuming a constant star formation rate since the creation of the tidal feature ( presumably \sim 3 \times 10 ^ { 8 } years ago ) , a total mass of \sim 7 \times 10 ^ { 5 } M _ { \odot } has been transformed from gas into stars .
Over this period , the star formation in the tidal arm has resulted in an additional enrichment of \Delta Z > 0.002 .
The reservoir of atomic and molecular gas in the tidal arm is \sim 3 \times 10 ^ { 8 } M _ { \odot } , allowing star formation to continue at its present rate for a Hubble time .
Such wide–spread , low–level star formation would be difficult to image around more distant galaxies but may be detectable through intervening absorption in quasar spectra .