We present new results for the molecular gas , dust emission and the ionized gas in J1023+1952 , an H i rich intergalactic star-forming tidal dwarf galaxy candidate .
It is located at the projected intersection of two faint stellar tidal streams wrapped around the interacting pair of galaxies NGC 3227/6 ( Arp 94 ) .
Using the IRAM 30m telescope , emission from ^ { 12 } CO ( 1-0 ) and ^ { 12 } CO ( 2-1 ) was detected across the entire extent of the neutral hydrogen cloud associated with J1023+1952 , a region of the size of 8.9 \times 5.9 kpc , as well as in the nuclear region and outer disk of NGC 3227 .
The molecular gas is found to be abundant over the entire H i cloud , with H _ { 2 } -to-H i gas mass ratios between 0.5 and 1.7 .
New Spitzer mid-infrared observations at 3.6 , 4.5 , 5.8 , 8.0 , 15 and 24 \mu m show that young SF is restricted to the southern part of the cloud .
Despite the relatively uniform H _ { 2 } and H i column density across the cloud , young SF occurs only in those regions where the velocity dispersion in the CO and H i is a factor of \sim two lower ( FWHM of 30 - 70 km s ^ { -1 } ) than elsewhere in the cloud ( FWHM of 80 - 120 km s ^ { -1 } ) .
Thus the kinematics of the gas , in addition to its column density , seems to be a crucial factor in triggering SF .
Optical/infrared spectral energy distributions ( SEDs ) and H \alpha photometry confirm that all the knots are young , with a tentative age sequence from the south-west ( oldest knots ) to the north-east ( youngest ) .
Optical spectroscopy of the brightest SF region allowed us to determine the metallicity ( 12+log ( O/H ) = 8.6 \pm 0.2 ) and the extinction ( A _ { B } =2.4 ) .
This shows that J1023+1952 is made from metal-enriched gas which is inconsistent with the hypothesis that it represents a pre-existing dwarf galaxy .
Instead , it must be formed from recycled , metal-enrichd gas , expelled from NGC 3227 or NGC 3226 in a previous phase of the interaction .