Scaling Relations of Spiral Galaxies

Abstract

We construct a large data set of global structural parameters for 1300 field and cluster spiral galaxies and explore the joint distribution of luminosity L, optical rotation velocity V, and disk size R at I and 2MASS K bands. The I- and K-band velocity-luminosity (VL) relations have log slopes of 0.29 and 0.27, respectively, with σ_(ln)(VL) ~ 0.13, and show a small dependence on color and morphological type in the sense that redder, earlier type disk galaxies rotate faster than bluer, later type disk galaxies for most luminosities. The VL relation at I and K bands is independent of surface brightness, size, and light concentration. The log slope of the I- and K-band size-luminosity (RL) relations is a strong function of morphology and varies from 0.25 to 0.5, with a mean of 0.32 for all Hubble types. At most luminosities, early-type disk galaxies have shorter scale lengths than later type ones. The average dispersion σ_(ln)(RL) decreases from 0.33 at I band to 0.29 at K, likely due to the 2MASS selection bias against lower surface brightness galaxies. The VL and RL residuals are largely uncorrelated with each other with a correlation coefficient r = -0.16 and Δ log V|L/Δ log R|L = -0.07 ± 0.01; the RV - RL residuals show a weak positive correlation with r = 0.53. These correlations suggest that scatter in luminosity is not a significant source of the scatter in the VL and RL relations. We discuss in two Appendices various pitfalls of standard analytical derivations of galaxy scaling relations, including the Tully-Fisher relation with different slopes. Our galaxy database is available at http://www.astro.queensu.ca/~courteau/data/VRL2007.dat.