Chemical Evidence for Morphological Evolution of Spiral Galaxies

Open Access
Publisher Website
Google Scholar
Abstract
Using the methods of spectrophotometric imagery and multislit spectroscopy, we have derived the radial abundance profiles from O/H measurements in 549 H II regions of eight early-type spiral galaxies. We then compared the characteristic abundance levels and radial distributions of this group of spirals with those of late-type galaxies. The early-type galaxies of our sample display gradients that are flatter and overall levels of O/H abundances that are higher than those of normal late-type galaxies. Early-type galaxies show an identical trend in the behavior of extrapolated central abundance versus morphological type to that shown by late-type galaxies with strong bars, even in the absence of a bar. On a diagram showing extrapolated central abundances versus morphological types, two clearly separated sequences appear: late-type barred galaxies and early-type (barred or unbarred) galaxies clearly fall on a sequence ~0.5 dex in abundance below that of normal late-type galaxies. This behavior is consistent with a scenario of morphological evolution of disk galaxies by the formation and dissolution of a bar over a period of a few 109 yr, where later type galaxies (Sd, Sc, Sbc) evolve into earlier-type disk galaxies (Sb, Sa) through transitory SBc and SBb phases.