GALAXY DISKS ARE SUBMAXIMAL

Journal Article · Sat Oct 01 04:00:00 EDT 2011 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/739/2/L47· OSTI ID:21565432

Bershady, Matthew A ^[1]; Martinsson, Thomas P. K.; Verheijen, Marc A. W.; Westfall, Kyle B ^[2]; Andersen, David R ^[3]

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1. Department of Astronomy, University of Wisconsin, 475 N. Charter St., Madison, WI 53706 (United States)
2. Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen (Netherlands)
3. NRC Herzberg Institute of Astrophysics, 5071 W Saanich Road, Victoria, BC V9E 2E7 (Canada)

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 ({sigma}{sup disk} {sub z,R=0}) is related to the maximum rotation speed (V {sub max}) as {sigma}{sup disk} {sub z,R=0} {approx} 0.26V {sub max}, consistent with previous measurements for edge-on disk galaxies and a mean stellar velocity ellipsoid axial ratio {alpha} {identical_to} {sigma} {sub z}/{sigma} {sub 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 (h{sub R} ), 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 h{sub R} even for the most extreme, fast-rotating disks (V {sub max} {>=} 300 km s{sup -1}) of the reddest rest frame, face-on color (B - K {approx} 4 mag), and highest luminosity (M{sub K} < -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.

• OSTI ID: 21565432
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 739; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ELECTROMAGNETIC RADIATION
GALAXIES
MASS
MOTION
RADIATIONS
ROTATION
STARS
VELOCITY
VISIBLE RADIATION