Galaxy Kinematics with VIRUS-P: The Dark Matter Halo of M87
Abstract
We present two-dimensional stellar kinematics of M87 out to R = 238'' taken with the integral field spectrograph VIRUS-P. We run a large set of axisymmetric, orbit-based dynamical models and find clear evidence for a massive dark matter halo. While a logarithmic parameterization for the dark matter halo is preferred, we do not constrain the dark matter scale radius for a Navarro-Frenk-White (NFW) profile and therefore cannot rule it out. Our best-fit logarithmic models return an enclosed dark matter fraction of 17.2+5.0 -5.0% within one effective radius (Re cong 100''), rising to 49.4+7.2 -8.8% within 2 Re . Existing SAURON data (R <=13''), and globular cluster (GC) kinematic data covering 145'' <= R <= 554'' complete the kinematic coverage to R = 47 kpc (~5 Re ). At this radial distance, the logarithmic dark halo comprises 85.3+2.5 -2.4% of the total enclosed mass of 5.7+1.3 -0.9 × 1012 M sun making M87 one of the most massive galaxies in the local universe. Our best-fit logarithmic dynamical models return a stellar mass-to-light ratio (M/L) of 9.1+0.2 -0.2 (V band), a dark halo circular velocity of 800+75 -25 km s-1, and a dark halo scale radius of 36+7 -3 kpc. The stellar M/L, assuming an NFW dark halo, is well constrained to 8.20+0.05 -0.10 (V band). The stars in M87 are found to be radially anisotropic out to R cong0.5 Re , then isotropic or slightly tangentially anisotropic to our last stellar data point at R = 2.4 Re where the anisotropy of the stars and GCs are in excellent agreement. The GCs then become radially anisotropic in the last two modeling bins at R = 3.4 Re and R = 4.8 Re . As one of the most massive galaxies in the local universe, constraints on both the mass distribution of M87 and anisotropy of its kinematic components strongly inform our theories of early-type galaxy formation and evolution in dense environments.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2011
- DOI:
- 10.1088/0004-637X/729/2/129
- arXiv:
- arXiv:1101.1957
- Bibcode:
- 2011ApJ...729..129M
- Keywords:
-
- dark matter;
- galaxies: elliptical and lenticular;
- cD;
- galaxies: kinematics and dynamics;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 15 figures, 29 pages, Accepted for publication in ApJ