STRUCTURE AND FORMATION OF S0 AND SPHEROIDAL GALAXIES
Title: STRUCTURE AND FORMATION OF S0 AND SPHEROIDAL GALAXIES
Speaker: John Kormendy (University of Texas at Austin)
Time: 10:30am on Thursday (Nov 1).
Place: The third floor lecture hall.
Abstract: We present observational evidence that Sph galaxies such as Fornax andNGC 205 are bulgeless S0 galaxies. Both are late-type galaxies that have beentransformed into gas-free, red and dead galaxies by a variety of internal andenvironmental processes. We update van den Bergh's parallel sequence galaxy classification in whichS0 galaxies form a sequence S0a-S0b-S0c that parallels the sequence Sa-Sb-Sc ofspiral galaxies. The ratio B/T of bulge to total light defines the position of agalaxy in this tuning fork diagram. Our classification makes a major improvement:We extend the S0a-S0b-S0c sequence to spheroidal (Sph) galaxies that are positionedin parallel to irregular galaxies in a similarly extended Sa-Sb-Sc-Im sequence.This provides a natural home for spheroidals, which previously were thought to below-surface-brightness ellipticals. To motivate our juxtaposition of spheroidalsand irregulars, we present photometry and bulge-disk decompositions of late-type S0sthat bridge the gap between the more common S0b and Sph galaxies. We find several S0s in the Virgo cluster that have B/T B/T <= 0.1. They are the S0cs that were missing from van den Bergh's paper. We update the structural parameter correlations of Sph, spiral, irregular, and elliptical galaxies. We show that spheroidals of increasing luminosity form a continuous sequence with the disks (but not bulges) of S0c-S0b-S0a galaxies. Remarkably, this Sph-S0-disk sequence is almost identical to that of irregular and spiral galaxies. We review the evidence for a variety of physical processes which we suggest transform gas-rich, star-forming S+Im galaxies into gas-poor S0+Sph galaxies.