Galaxy disks are submaximal

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Journal titleThe Astrophysical Journal Letters
PagesL47-1L47-4; # of pages: 4
Subjectgalaxies: formation; galaxies: fundamental parameters; galaxies: halos; galaxies: kinematics and dynamics; galaxies: spiral; galaxies: stellar content
AbstractWe 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.
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AffiliationNational Research Council Canada; NRC Herzberg Institute of Astrophysics
Peer reviewedYes
NPARC number19809250
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Record identifier60e20f71-a68f-4344-baa6-5b37b5609dc1
Record created2012-04-13
Record modified2016-05-09
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