Volume 557, September 2013
|Number of page(s)||52|
|Published online||20 September 2013|
The DiskMass Survey
VII. The distribution of luminous and dark matter in spiral galaxies⋆
1 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
e-mail: firstname.lastname@example.org; email@example.com
2 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
3 Department of Astronomy, University of Wisconsin, 475 N. Charter St., Madison, WI 53706, USA
4 NRC Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, British Columbia, Canada V9E 2E7, Canada
5 National Optical Astronomy Observatory, 950 North Cherry Ave., Tucson, AZ 85719, USA
Received: 1 March 2013
Accepted: 12 July 2013
We present dynamically-determined rotation-curve mass decompositions of 30 spiral galaxies, which were carried out to test the maximum-disk hypothesis and to quantify properties of their dark-matter halos. We used measured vertical velocity dispersions of the disk stars to calculate dynamical mass surface densities (Σdyn). By subtracting our observed atomic and inferred molecular gas mass surface densities from Σdyn, we derived the stellar mass surface densities (Σ∗), and thus have absolute measurements of all dominant baryonic components of the galaxies. Using K-band surface brightness profiles (IK), we calculated the K-band mass-to-light ratio of the stellar disks (Υ∗ = Σ∗/IK) and adopted the radial mean () for each galaxy to extrapolate Σ∗ beyond the outermost kinematic measurement. The derived of individual galaxies are consistent with all galaxies in the sample having equal Υ∗. We find a sample average and scatter of ⟨⟩ = 0.31 ± 0.07. Rotation curves of the baryonic components were calculated from their deprojected mass surface densities. These were used with circular-speed measurements to derive the structural parameters of the dark-matter halos, modeled as either a pseudo-isothermal sphere (pISO) or a Navarro-Frenk-White (NFW) halo. In addition to our dynamically determined mass decompositions, we also performed alternative rotation-curve decompositions by adopting the traditional maximum-disk hypothesis. However, the galaxies in our sample are submaximal, such that at 2.2 disk scale lengths (hR) the ratios between the baryonic and total rotation curves (Fb2.2hR) are less than 0.75. We find this ratio to be nearly constant between 1–6hR within individual galaxies. We find a sample average and scatter of ⟨Fb2.2hR⟩ = 0.57 ± 0.07, with trends of larger Fb2.2hR for more luminous and higher-surface-brightness galaxies. To enforce these being maximal, we need to scale Υ∗ by a factor 3.6 on average. In general, the dark-matter rotation curves are marginally better fit by a pISO than by an NFW halo. For the nominal-Υ∗ (submaximal) case, we find that the derived NFW-halo parameters have values consistent with ΛCDM N-body simulations, suggesting that the baryonic matter in our sample of galaxies has only had a minor effect on the dark-matter distribution. In contrast, maximum-Υ∗ decompositions yield halo-concentration parameters that are too low compared to the ΛCDM simulations.
Key words: techniques: imaging spectroscopy / galaxies: spiral / galaxies: structure / galaxies: kinematics and dynamics / galaxies: fundamental parameters
Appendix is available in electronic form at http://www.aanda.org
© ESO, 2013
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