The Luminosity-Metallicity Relation, Effective Yields, and Metal Loss in Spiral and Irregular Galaxies

I present results on the correlation between galaxy mass, luminosity, and metallicity for a sample of spiral and irregular galaxies having well-measured abundance profiles, distances, and rotation speeds. Additional data for low surface brightness galaxies from the literature are also included for comparison. These data are combined to study the metallicity-luminosity and metallicityrotation speed correlations for spiral and irregular galaxies. The metallicity luminosity correlation shows its familiar form for these galaxies, a roughly uniform change in the average present-day O/H abundance of about a factor 100 over 11 magnitudes in B luminosity. However, the O/H Vrot relation shows a change in slope at a rotation speed of about 125 km s . At faster Vrot, there appears to be no relation between average metallicity and rotation speed. At lower Vrot, the metallicity correlates with rotation speed. This change in behavior could be the result of increasing loss of metals from the smaller galaxies in supernova-driven winds. This idea is tested by looking at the variation in effective yield, derived from observed abundances and gas fractions assuming closed box chemical evolution. The effective yields derived for spiral and irregular galaxies increase by a factor of 10-20 from Vrot ≈ 5 km s −1 to Vrot ≈ 300 km s, asympotically increasing to approximately constant yeff for Vrot & 150 km s. The trend suggests that galaxies with Vrot . 100-150 km s −1 may lose a large fraction of their SN ejecta, while galaxies above this value tend to retain metals. Subject headings: Galaxies: abundances — galaxies: evolution — galaxies: spiral — galaxies: irregular