THE STRUCTURE AND DYNAMICS OF MASSIVE EARLY-TYPE GALAXIES: ON HOMOLOGY, ISOTHERMALITY, AND ISOTROPY INSIDE ONE EFFECTIVE RADIUS
Author(s)Koopmans, L. V. E.; Bolton, Adam S.; Treu, T.; Czoske, O.; Auger, M. W.; Barnabe, M.; Vegetti, S.; Gavazzi, R.; Moustakas, L. A.; Burles, Scott; ... Show more Show less
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Based on 58 SLACS strong-lens early-type galaxies (ETGs) with direct total-mass and stellar-velocity dispersion measurements, we find that inside one effective radius massive elliptical galaxies with Meff [> over ~] 3 × 10[superscript 10] M[superscript ☉] are well approximated by a power-law ellipsoid, with an average logarithmic density slope of 〈γ'LD〉 ≡ −dlog(ρ[subscript tot]) [over dlog(r)] = 2.085[superscript +0.025 subscript −0.018] (random error on mean) for isotropic orbits with β[subscript r] = 0, ±0.1 (syst.) and σ[subscript γ'] [< over ~] 0.20 [superscript +0.04 subscript -0.02] intrinsic scatter (all errors indicate the 68% CL). We find no correlation of γ'[subscript LD] with galaxy mass (M[subscript eff]), rescaled radius (i.e., R[subscript einst] [over R[subscript eff]]) or redshift, despite intrinsic differences in density-slope between galaxies. Based on scaling relations, the average logarithmic density slope can be derived in an alternative manner, fully independent from dynamics, yielding 〈γ'[subscript SR]〉 = 1.959 ± 0.077. Agreement between the two values is reached for 〈β[subscript r]〉 = 0.45 ± 0.25, consistent with mild radial anisotropy. This agreement supports the robustness of our results, despite the increase in mass-to-light ratio with total galaxy mass: M[subscript eff] ∝ L[superscript 1.363±0.056 subscript V,eff]. We conclude that massive ETGs are structurally close to homologous with close to isothermal total density profiles ([< over ~]10% intrinsic scatter) and have at most some mild radial anisotropy. Our results provide new observational limits on galaxy formation and evolution scenarios, covering 4 Gyr look-back time.
DepartmentMassachusetts Institute of Technology. Department of Physics; MIT Kavli Institute for Astrophysics and Space Research
Koopmans, L. V. E., A. Bolton, T. Treu, O. Czoske, M. W. Auger, M. Barnabè, S. Vegetti, R. Gavazzi, L. A. Moustakas, and S. Burles. “THE STRUCTURE AND DYNAMICS OF MASSIVE EARLY-TYPE GALAXIES: ON HOMOLOGY, ISOTHERMALITY, AND ISOTROPY INSIDE ONE EFFECTIVE RADIUS.” The Astrophysical Journal 703, no. 1 (September 2, 2009): L51–L54. © 2009 The American Astronomical Society
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