Astronomy seminar to be held in UCD:
Title: Massive Star Formation along the Hubble Sequence
Speaker: Prof. Nicholas Devereux, Fulbright scholar, NUI Galway
Date: Thursday, March 15th, 2007
Room: 128 UCD School of Physics, Science Centre North, Belfield
Tea afterwards in the common room
New results, based on one of the most comprehensive H-alpha imaging surveys of nearby Sa-Sab spirals completed to date, reveals early-type spirals to be a diverse group of galaxies that span a wide range in massive star formation rates. While the majority of Sa-Sab galaxies in our sample are forming stars at a modest rate, a significant fraction (~29%) exhibit star formation rates greater than 1 Msolar yr-1, rivaling the most prolifically star-forming late-type spirals. A similar diversity is apparent in the star formation history of Sa-Sab spirals as measured by their H-alpha equivalent widths. Consistent with our preliminary results presented in the first paper in this series, we find giant H II regions [L(H?)>=10^39 ergs s-1] in the disks of ~37% of early-type spirals. We suspect that recent minor mergers or past interactions are responsible for the elevated levels of H-alpha emission and, perhaps, for the presence of giant H II regions in these galaxies. Our results, how ever, are not in total agreement with the H-alpha study of Kennicutt & Kent, who did not find any early-type spirals with H-alpha equivalent widths >14 Å. A close examination of the morphological classification of galaxies, however, suggests that systematic differences between the Revised Shapley-Ames Catalog and the Second Reference Catalogue may be responsible for the contrasting results.