A multi-band analysis of the region containing the supergiant H i shell in the nearby dwarf irregular galaxy IC 2574 presents evidence of a causal relationship between a central star cluster , the surrounding expanding H i shell , and secondary star formation sites on the rim of the H i shell .
Comparisons of the far–UV ( FUV , 1521 Å ) , optical broad-band , H \alpha , X-ray , and H i morphologies suggest that the region is in an auspicious moment of star formation triggered by the central stellar cluster .
The derived properties of the H i shell , the central stellar cluster , and the star forming regions on the rim support this scenario : The kinematic age of the H i shell is < 14 Myr and in agreement with the age of the central stellar cluster derived from the FUV observations ( \sim 11 Myr ) .
An estimate for the mechanical energy input from SN and stellar winds of the central stellar cluster made from FUV photometry and the derived cluster age is 4.1 \times 10 ^ { 52 } erg , roughly a few times higher than the kinetic energy of the H i shell .
The requisite energy input needed to create the H i shell , derived in the ‘ standard ’ fashion from the HI observations ( using the numerical models of Chevalier ) , is 2.6 \times 10 ^ { 53 } erg which is almost an order of magnitude higher than the estimated energy input as derived from the FUV data .
Given the overwhelming observational evidence that the central cluster is responsible for the expanding H i shell , this discrepancy suggests that the required energy input is overestimated using the ‘ standard ’ method .
This may explain why some other searches for remnant stellar clusters in giant H i holes have been unsuccessful so far .
Our observations also show that stellar clusters are indeed able to create supergiant H i shells , even at large galactocentric radii , a scenario which has recently been questioned by a number of authors .