Dwarf Galaxy Dark Matter Density Profiles Inferred From Stellar And Gas Kinematics

Date
2014-07
Authors
Adams, Joshua J.
Simon, Joshua D.
Fabricius, Maximilian H.
van den Bosch, Remco C. E.
Barentine, John C.
Bender, Ralf
Gebhardt, Karl
Hill, Gary J.
Murphy, Jeremy D.
Swaters, R. A.
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Abstract

We present new constraints on the density profiles of dark matter (DM) halos in seven nearby dwarf galaxies from measurements of their integrated stellar light and gas kinematics. The gas kinematics of low-mass galaxies frequently suggest that they contain constant density DM cores, while N-body simulations instead predict a cuspy profile. We present a data set of high-resolution integral-field spectroscopy on seven galaxies and measure the stellar and gas kinematics simultaneously. Using Jeans modeling on our full sample, we examine whether gas kinematics in general produce shallower density profiles than are derived from the stars. Although two of the seven galaxies show some localized differences in their rotation curves between the two tracers, estimates of the central logarithmic slope of the DM density profile, gamma, are generally robust. The mean and standard deviation of the logarithmic slope for the population are gamma = 0.67 +/- 0.10 when measured in the stars and gamma = 0.58 +/- 0.24 when measured in the gas. We also find that the halos are not under-concentrated at the radii of half their maximum velocities. Finally, we search for correlations of the DM density profile with stellar velocity anisotropy and other baryonic properties. Two popular mechanisms to explain cored DM halos are an exotic DM component or feedback models that strongly couple the energy of supernovae into repeatedly driving out gas and dynamically heating the DM halos. While such models do not yet have falsifiable predictions that we can measure, we investigate correlations that may eventually be used to test models. We do not find a secondary parameter that strongly correlates with the central DM density slope, but we do find some weak correlations. The central DM density slope weakly correlates with the abundance of a elements in the stellar population, anti-correlates with Hi fraction, and anti-correlates with vertical orbital anisotropy. We expect, if anything, the opposite of these three trends for feedback models. Determining the importance of these correlations will require further model developments and larger observational samples.

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Citation
Adams, Joshua J., Joshua D. Simon, Maximilian H. Fabricius, Remco CE van den Bosch, John C. Barentine, Ralf Bender, Karl Gebhardt et al. "Dwarf galaxy dark matter density profiles inferred from stellar and gas kinematics." The Astrophysical Journal, Vol. 789, No. 1 (Jul., 2014): 63.