A METHOD FOR MEASURING (SLOPES OF) THE MASS PROFILES OF DWARF SPHEROIDAL GALAXIES
- Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB30HA (United Kingdom)
We introduce a method for measuring the slopes of mass profiles within dwarf spheroidal (dSph) galaxies directly from stellar spectroscopic data and without adopting a dark matter halo model. Our method combines two recent results: (1) spherically symmetric, equilibrium Jeans models imply that the product of half-light radius and (squared) stellar velocity dispersion provides an estimate of the mass enclosed within the half-light radius of a dSph stellar component, and (2) some dSphs have chemodynamically distinct stellar subcomponents that independently trace the same gravitational potential. We devise a statistical method that uses measurements of stellar positions, velocities, and spectral indices to distinguish two dSph stellar subcomponents and to estimate their individual half-light radii and velocity dispersions. For a dSph with two detected stellar subcomponents, we obtain estimates of masses enclosed at two discrete points in the same mass profile, immediately defining a slope. Applied to published spectroscopic data, our method distinguishes stellar subcomponents in the Fornax and Sculptor dSphs, for which we measure slopes {Gamma} {identical_to} {Delta}log M/{Delta}log r = 2.61{sup +0.43}{sub -0.37} and {Gamma} = 2.95{sup +0.51}{sub -0.39}, respectively. These values are consistent with 'cores' of constant density within the central few hundred parsecs of each galaxy and rule out 'cuspy' Navarro-Frenk-White (NFW) profiles (dlog M/dlog r {<=} 2 at all radii) with a significance {approx}> 96% and {approx}> 99%, respectively. Tests with synthetic data indicate that our method tends systematically to overestimate the mass of the inner stellar subcomponent to a greater degree than that of the outer stellar subcomponent, and therefore to underestimate the slope {Gamma} (implying that the stated NFW exclusion levels are conservative).
- OSTI ID:
- 21612641
- Journal Information:
- Astrophysical Journal, Vol. 742, Issue 1; Other Information: DOI: 10.1088/0004-637X/742/1/20; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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