Dark Matter within High Surface Brightness Spiral Galaxies

Abstract

We present results from a detailed dynamical analysis of five high surface brightness, late-type spiral galaxies, NGC 3810, NGC 3893, NGC 4254, NGC 5676, and NGC 6643, which were studied with the aim of quantifying the luminous-to-dark matter ratio inside their optical radii. The galaxies' stellar light distribution and gas kinematics have been observed and compared to hydrodynamic gas simulations that predict the gasdynamics arising in response to empirical gravitational potentials, which are combinations of differing stellar disk and dark halo contributions. The gravitational potential of the stellar disk was derived from nearinfrared photometry, color corrected to yield a constant stellar mass-to-light ratio (M/L); for the dark halo, the mass density distribution of an axisymmetric isothermal sphere with a core was chosen. Hydrodynamic gas simulations were performed for each galaxy for a sequence of five different mass fractions of the stellar disk and for a wide range of spiral pattern speeds. These two parameters mainly determine the modeled gas distribution and kinematics. The agreement between the simulated and observed gas kinematics permitted us to conclude that the galaxies with the highest rotation velocities tend to possess very massive stellar disks that dominate the gasdynamics within the optical radius. In less massive galaxies, with a maximal rotation velocity of less than 200 km s À1 , the mass of the dark halo at least equals the stellar mass within 2-3 disk scale lengths. The maximal disk stellar mass-to-light ratio in the K band was found to lie at about M=L K % 0:6. Furthermore, the gasdynamic simulations provide a powerful tool for accurately determining the dominant spiral pattern speed for galaxies, independent of a specific density wave theory. It was found that the location of the corotation resonance falls into a narrow range of around three exponential disk scale lengths for all galaxies from the sample. The corotation resonance encloses the strong part of the stellar spiral in all cases. Based on the experience gained from this project, the use of a color correction to account for local stellar population differences is strongly encouraged when properties of galactic disks are studied that rely on their stellar mass distributions.

The DiskMass Survey

“…They found that maximum-disk values are highly favored for this galaxy, and argued that the luminous matter dominates inside the optical radius of high surface brightness disk galaxies in general. Kranz et al (2003) studied five high surface brightness late-type spiral galaxies using hydrodynamic gas simulations and draw the conclusion that high surface brightness galaxies possess maximal disks if their maximal A131, page 16 of 52 rotation velocities are larger than 200 km s −1 . If the maximal rotation velocity is less, the galaxies appear to have submaximal disks.…”

“…However, observations have so far not lead to a consensus, and the maximality may depend on the galaxy type (Bottema 1993;Weiner et al 2001;Kranz et al 2003;Kregel et al 2005;Byrd et al 2006;Herrmann & Ciardullo 2009;Dutton et al 2011Dutton et al , 2013Barnabè et al 2012).…”

Bars and Dark Matter Halo Cores

“…Englmaier & Gerhard (1999), Weiner, Sellwood, & Williams (2001), and Kranz, Slyz, & Rix (2003) have made dynamical estimates of the disk mass, finding generally that the disk dominates the inner galaxy and that the DM halo has a very low central density. Binney & Evans (2001) also argue, although slightly less directly, for a low central density in the Milky Way.…”

Numerical Simulations of KPG 302 (NGC 3893/96)

“…For example, the pitch angle of the spiral pattern of NGC 3893 measured by Kranz et al (2003) from NIR observations is of 19 degrees while the numerical simulations predict pitch angles that depend on the density distribution of the DM halo being better suited those with pseudo-isothermal density profiles. We are still conducting comprehensive sets of simulations in order to take into account the different observations on this galaxy pair.…”