Galaxy Disks are Submaximal

Type Journal Article
Names Matthew A. Bershady, Thomas P. K. Martinsson, Marc A. W. Verheijen, Kyle B. Westfall, David R. Andersen, Rob A. Swaters
Publication The Astrophysical Journal Letters
Volume 739
Issue 2
Pages L47
Date October 1, 2011
URL http://adsabs.harvard.edu/abs/2011ApJ...739L..47B
Library Catalog NASA ADS
Abstract We measure the contribution of galaxy disks to the overall gravitational potential of 30 nearly face-on intermediate-to-late-type spirals from the DiskMass Survey. The central vertical velocity dispersion of the disk stars (σdisk z, R = 0) is related to the maximum rotation speed (V max) as σdisk z, R = 0 ~ 0.26V max, consistent with previous measurements for edge-on disk galaxies and a mean stellar velocity ellipsoid axial ratio α ≡ σ z /σ R = 0.6. For reasonable values of disk oblateness, this relation implies these galaxy disks are submaximal. We find disks in our sample contribute only 15%-30% of the dynamical mass within 2.2 disk scale lengths (hR ), with percentages increasing systematically with luminosity, rotation speed, and redder color. These trends indicate that the mass ratio of disk-to-total matter remains at or below 50% at 2.2 hR even for the most extreme, fast-rotating disks (V max >= 300 km s-1) of the reddest rest frame, face-on color (B - K ~ 4 mag), and highest luminosity (MK < -26.5 mag). Therefore, spiral disks in general should be submaximal. Our results imply that the stellar mass-to-light ratio and hence the accounting of baryons in stars should be lowered by at least a factor of three.
Tags GALAXIES: FUNDAMENTAL PARAMETERS, GALAXIES: STELLAR CONTENT, Galaxies: Halos, galaxies: formation, galaxies: kinematics and dynamics, galaxies: spiral
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