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1994PASP..106..424M - Publ. Astron. Soc. Pac., 106, 424-424 (1994/April-0)
Star formation in giant extragalactic HII regions. (Dissertation summary).
MAYYA Y.D.
Abstract (from CDS):
Differential reddening between gas and embedded stars is essential to constrain the dereddened cluster colors within the range of youngest clusters. Obscuring dust closely associated with gas, which is distributed in filaments and clumps, as in the case of 30 Doradus, is the most likely configuration giving rise to net reduction of extinction towards stars. The fraction of the stellar photons escaping the nebula unattenuated is estimated to be 50%.
GEHRs are rarely found to be simple systems containing stars from single generation. In the present sample such regions in addition to being older than 3∼Myr, have their Lyman continuum luminosity reduced by as much as 60%, compared to the observed B band luminosity for a normal IMF. The missing ionizing photons may be escaping the nebula, leading to the ionization of extra-H II region ionized medium.
Co-existence of young (age ≤ 5 Myr; stars producing ionizing photons) and old populations (∼10∼Myr; Red Supergiants) is found to be common in GEHRs. The emission and continuum knots are seen spatially separated (40-100 pc) on CCD images in NGC 2997, 4303 and 4449 and may be direct evidences for the co-existence of young and old populations in giant star forming complexes. Triggering of star formation from earlier bursts is the most likely cause of new generation of stars, and may be a common phenomenon in GEHRs. Spatial separation between the young and old stars (∼30 pc) had been earlier reported in 30 Doradus. Thus GEHRs in nearby galaxies share many of the properties shown by 30 Dor, the nearest GEHR.
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Simbad objects: 11
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