The Gravitational Potential near the Sun from SEGUE Kdwarf Kinematics
Abstract
To constrain the Galactic gravitational potential near the Sun (~1.5 kpc), we derive and model the spatial and velocity distributions for a sample of 9000 Kdwarfs with spectra from SDSS/SEGUE, which yield radial velocities and abundances ([Fe/H] and [α/Fe]). We first derive the spatial density distribution for three abundanceselected subpopulations of stars accounting for the survey's selection function. The vertical profiles of these subpopulations are simple exponentials and their vertical dispersion profile is nearly isothermal. To model these data, we apply the "vertical" Jeans equation, which relates the observable tracer number density and vertical velocity dispersion to the gravitational potential or vertical force. We explore a number of functional forms for the vertical force law, fit the dispersion and density profiles of all abundanceselected subpopulations simultaneously in the same potential, and explore all parameter covariances using a Markov Chain Monte Carlo technique. Our fits constrain a disk mass scale height <~ 300 pc and the total surface mass density to be 67 ± 6 M _{⊙} pc^{2} at z = 1.0 kpc of which the contribution from all stars is 42 ± 5 M _{⊙} pc^{2} (assuming a contribution from cold gas of 13 M _{⊙} pc^{2}). We find significant constraints on the local dark matter density of 0.0065 ± 0.0023 M _{⊙} pc^{3} (0.25 ± 0.09 GeV cm^{3}). Together with recent experiments this firms up the best estimate of 0.0075 ± 0.0021 M _{⊙} pc^{3} (0.28 ± 0.08 GeV cm^{3}), consistent with global fits of approximately round dark matter halos to kinematic data in the outskirts of the Galaxy.
 Publication:

The Astrophysical Journal
 Pub Date:
 August 2013
 DOI:
 10.1088/0004637X/772/2/108
 arXiv:
 arXiv:1209.0256
 Bibcode:
 2013ApJ...772..108Z
 Keywords:

 Galaxy: kinematics and dynamics;
 Galaxy: structure;
 solar neighborhood;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 46 pages, 13 figures, 1 table, accepted for publication in The Astrophysical Journal