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

I present results on the correlation between galaxy mass, luminosity, andmetallicity for a sample of spiral and irregular galaxies having well-measuredabundance profiles, distances, and rotation speeds. Additional data for lowsurface brightness galaxies from the literature are also included forcomparison. These data are combined to study the metallicity-luminosity andmetallicity-rotation speed correlations for spiral and irregular galaxies. Themetallicity luminosity correlation shows its familiar form for these galaxies,a roughly uniform change in the average present-day O/H abundance of about afactor 100 over 11 magnitudes in B luminosity. However, the O/H - V(rot)relation shows a change in slope at a rotation speed of about 125 km/sec. Atfaster V(rot), there appears to be no relation between average metallicity androtation speed. At lower V(rot), the metallicity correlates with rotationspeed. This change in behavior could be the result of increasing loss of metalsfrom the smaller galaxies in supernova-driven winds. This idea is tested bylooking at the variation in effective yield, derived from observed abundancesand gas fractions assuming closed box chemical evolution. The effective yieldsderived for spiral and irregular galaxies increase by a factor of 10-20 fromV(rot) approximately 5 km/sec to V(rot) approximately 300 km/sec, asympoticallyincreasing to approximately constant y(eff) for V(rot) > 150 km/sec. The trendsuggests that galaxies with V(rot) < 100-150 km/sec may lose a large fractionof their SN ejecta, while galaxies above this value tend to retain metals.Comment: 40 pages total, including 7 encapsulated postscript figures. Accepted for publication in 20 Dec 2002 Ap