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J. F. Helmboldt (UNM/NMSU), R. A. M. Walterbos (NMSU), T. Goto (JAXA/ISAS)
We present the results of H\alpha and broad-band imaging of seven nearby star-forming early-type galaxies drawn from a larger (1,108 galaxies) sample of star-forming early-type SDSS galaxies that are consistent with being the progenitors of so-called E+A (or K+A) galaxies. Specifically, we use these images to examine (1) the location and physical extent of the star forming regions, (2) the influence of the star formation on the galaxies' morphologies, and (3) the possible implications regarding the role similar star formation episodes, which can lead to E+A galaxies, may play in the morphological evolution of field galaxies. The size of the H\alpha emission within these galaxies ranges from 0.6 to 6 kpc; the average size is ~3 kpc in diameter. The average radial extent of the star formation is about 50% of the half light radius of each galaxy. In all but one case (which is likely a merging system), the star formation is centralized. Even for the two galaxies that have noticeable spiral arms, the vast majority of the star formation is not contained within the disks, but within the bulge components. The impact this centralized star formation may have on morphology is explored using detailed modeling of the star formation histories of the larger parent sample of star-forming early-type galaxies. We used the modeling results along with star formation rates derived from the integrated H\alpha luminosities for the seven galaxies imaged to compute the increase in the stellar masses of the bulge components due to the star formation. We found that the star formation in these objects is too weak to produce any substantial change in the galaxies' bulge fractions but is capable of affecting smaller morphological changes analogous to nuclear stellar disks or the inner surface brightness profiles of so-called "power law" early-type galaxies.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.