The structure and dark halo core properties of dwarf spheroidal galaxies
- University Observatory Munich (USM), Scheinerstrasse 1, D-81679 Munich (Germany)
- (MPE), Giessenbachstr. 1, D-85748 Garching (Germany)
The structure and dark matter halo core properties of dwarf spheroidal galaxies (dSphs) are investigated. A double-isothermal (DIS) model of an isothermal, non-self-gravitating stellar system embedded in an isothermal dark halo core provides an excellent fit to the various observed stellar surface density distributions. The stellar core scale length a{sub *} is sensitive to the central dark matter density ρ{sub 0,d}. The maximum stellar radius traces the dark halo core radius r{sub c,d}. The concentration c{sub *} of the stellar system, determined by a King profile fit, depends on the ratio of the stellar-to-dark-matter velocity dispersion σ{sub ∗}/σ{sub d}. Simple empirical relationships are derived that allow us to calculate the dark halo core parameters ρ{sub 0,d}, r{sub c,d}, and σ{sub d} given the observable stellar quantities σ{sub *}, a{sub *}, and c{sub *}. The DIS model is applied to the Milky Way’s dSphs. All dSphs closely follow the same universal dark halo scaling relations ρ{sub 0,d}×r{sub c,d}=75{sub −45}{sup +85} M{sub ⊙} pc{sup −2} that characterize the cores of more massive galaxies over a large range in masses. The dark halo core mass is a strong function of core radius, M{sub c,d}∼r{sub c,d}{sup 2}. Inside a fixed radius of ∼400 pc the total dark matter mass is, however, roughly constant with M{sub d}=2.6±1.4×10{sup 7} M{sub ⊙}, although outliers are expected. The dark halo core densities of the Galaxy’s dSphs are very high, with ρ{sub 0,d} ≈ 0.2 M{sub ⊙} pc{sup −3}. dSphs should therefore be tidally undisturbed. Evidence for tidal effects might then provide a serious challenge for the CDM scenario.
- OSTI ID:
- 22882841
- Journal Information:
- Astrophysical Journal, Vol. 808, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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