The DiskMass Survey. IV. The Dark-matter-dominated Galaxy UGC 463

Type Journal Article
Names Kyle B. Westfall, Matthew A. Bershady, Marc A. W. Verheijen, David R. Andersen, Thomas P. K. Martinsson, Robert A. Swaters, Andrew Schechtman-Rook
Publication The Astrophysical Journal
Volume 742
Issue 1
Pages 18
Date November 1, 2011
URL http://adsabs.harvard.edu/abs/2011ApJ...742...18W
Library Catalog NASA ADS
Abstract We present a detailed and unique mass budget for the high surface brightness galaxy UGC 463, showing it is dominated by dark matter (DM) at radii beyond one scale length (hR ) and has a baryonic-to-DM mass ratio of approximately 1:3 within 4.2hR . Assuming a constant scale height (hz ; calculated via an empirical oblateness relation), we calculate dynamical disk mass surface densities from stellar kinematics, which provide vertical velocity dispersions after correcting for the shape of the stellar velocity ellipsoid (measured to have σθ/σ R = 1.04 ± 0.22 and σ z /σ R = 0.48 ± 0.09). We isolate the stellar mass surface density by accounting for all gas mass components and find an average K-band mass-to-light ratio of 0.22+/- 0.09(ran) ^{+0.16}_{-0.15}(sys) \, {M}_\odot / {L}_\odot ^K; Zibetti et al. and Bell et al. predict, respectively, 0.56 and 3.6 times our dynamical value based on stellar-population-synthesis modeling. The baryonic matter is submaximal by a factor of ~3 in mass and the baryonic-to-total circular-speed ratio is 0.61+0.07 -0.09(ran)+0.12 -0.18(sys) at 2.2hR ; however, the disk is globally stable with a multi-component stability that decreases asymptotically with radius to Q ~ 2. We directly calculate the circular speed of the DM halo by subtracting the baryonic contribution to the total circular speed; the result is equally well described by either a Navarro-Frenk-White halo or a pseudo-isothermal sphere. The volume density is dominated by DM at heights of |z| >~ 1.6hz for radii of R >~ hR . As is shown in follow-up papers, UGC 463 is just one example among nearly all galaxies we have observed that contradict the hypothesis that high surface brightness spiral galaxies have maximal disks.
Tags GALAXIES: FUNDAMENTAL PARAMETERS, GALAXIES: STRUCTURE, dark matter, galaxies: individual: UGC 463, galaxies: kinematics and dynamics, galaxies: spiral
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