Stephan ’ s Quintet ( SQ ) is a system consisting of at least four interacting galaxies which is well known for its complex dynamical and star formation history .
It possesses a rich intergalactic medium ( IGM ) , where hydrogen clouds , both atomic and molecular , associated with two starbursts ( refered to as SQ A and B ) have been found .
In order to study the extent , origin and fate of the intergalactic molecular gas and its relation to the formation of stars outside galaxies and Tidal Dwarf Galaxies ( TDGs ) , we mapped with the IRAM 30m antenna the carbon monoxide ( CO ) towards several regions of the IGM in SQ .
In both SQ A and B , we detected unusually large amounts of molecular gas ( 3.1 \times 10 ^ { 9 } M _ { \odot } and 7 \times 10 ^ { 8 } M _ { \odot } , respectively ) .
In contrast , no significant CO detection was achieved towards HII regions south of the pair NGC 7318a/b despite their high H \alpha luminosities .
The molecular gas is very extended in both SQ A and SQ B , over areas of between 15 and 25 kpc .
The CO clouds seem to have otherwise different properties and may be of a different nature .
The integrated CO line of SQ A is in particular much wider than in SQ B .
Its CO spectrum shows emission at two velocities ( 6000 and 6700 km s ^ { -1 } ) that are coincident with two HI lines .
The strongest emission at 6000 km s ^ { -1 } is however spatially offset from the HI emission and situated on a ridge south-east of the starburst region .
In SQ B the CO emission coincides with that of tracers of star formation ( H \alpha , 15 \mu m and radio continuum ) .
The CO peak lies slightly offset from the HI peak towards a steep HI gradient .
This is indicating that the molecular gas is forming in-situ , possibly in a region of compressed HI , with subsequent star formation .
The star forming region at SQ B is the object in SQ that most resembles a TDG .