We present Arecibo Legacy Fast ALFA ( ALFALFA ) and follow-up Giant Metrewave Radio Telescope ( GMRT ) H i observations of the gas-rich interacting group NGC 3166/9 .
The sensitive ALFALFA data provide a complete census of H i -bearing systems in the group while the high-resolution GMRT data elucidate their origin , enabling one of the first unbiased physical studies of gas-rich dwarf companions and the subsequent identification of second-generation , tidal dwarf galaxies in a nearby group .
The ALFALFA maps reveal an extended H i envelope around the NGC 3166/9 group core , which we mosaic at higher resolution using six GMRT pointings spanning \sim 1 square degree .
A thorough search of the GMRT datacube reveals eight low-mass objects with gas masses ranging from 4 \times 10 ^ { 7 } to 3 \times 10 ^ { 8 } M _ { \odot } and total dynamical masses up to 1.4 \times 10 ^ { 9 } M _ { \odot } .
A comparison of the H i fluxes measured from the GMRT data to those measured in the ALFALFA data suggests that a significant fraction ( \sim 60 \% ) of the H i is smoothly distributed on scales greater than an arcminute ( \sim 7 kpc at the NGC 3166/9 distance ) .
We compute stellar masses and star formation rates for the eight low-mass GMRT detections , using ancillary SDSS and GALEX data , and use these values to constrain their origin .
Most of the detections are likely to be either pre-existing dwarf irregular galaxies or short-lived , tidally formed knots ; however , one candidate , AGC 208457 , is clearly associated with a tidal tail extending below NGC 3166 , exhibits a dynamical to gas mass ratio close to unity and has a stellar content and star formation rate that are broadly consistent with both simulated as well as candidate tidal dwarf galaxies from the literature .
Our observations therefore strongly suggest that AGC 208457 is a tidal dwarf galaxy .