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Title: A UNIVERSAL POWER-LAW PROFILE OF PSEUDO-PHASE-SPACE DENSITY-LIKE QUANTITIES IN ELLIPTICAL GALAXIES

We study profiles of mass density, velocity dispersion (VD), and a combination of both using ∼2000 nearly spherical and rotation-free Sloan Digital Sky Survey galaxies. For observational stellar mass density ρ{sub *}(r), we consider a range of dark matter (DM) distribution ρ{sub DM}(r) and VD anisotropy β(r) to investigate radial stellar VD σ{sub *r}(r) using the spherical Jeans equation. While mass and VD profiles vary appreciably depending on DM distribution and anisotropy, the pseudo-phase-space density-like combination ρ(r)/σ{sub ⋆r}{sup 3}(r) with total density ρ(r) = ρ{sub *}(r) + ρ{sub DM}(r) is nearly universal. In the optical region, the negative logarithmic slope has a mean value of (χ) ≈ 1.86-1.90 with a galaxy-to-galaxy rms scatter of ≈0.04-0.06, which is a few times smaller than that of ρ(r) profiles. The scatter of χ can be increased by invoking wildly varying anisotropies that are, however, less likely because they would produce too large a scatter of line of sight VD profiles. As an independent check of this universality, we analyze stellar orbit-based dynamical models of 15 early-type galaxies (ETGs) of the Coma cluster provided by J. Thomas. Coma ETGs, with σ{sub *r}(r) replaced by the rms velocity of stars v {sub *rms}(r) including netmore » rotation, exhibit a similar universality with a slope of χ = 1.93 ± 0.06. Remarkably, the inferred values of χ for ETGs match well the slope ≈1.9 predicted by N-body simulations of DM halos. We argue that the inferred universal nature of ρ(r)/σ{sub ⋆r}{sup 3}(r) cannot be fully explained by equilibrium alone, implying that some astrophysical factors conspire and/or it reflects a fundamental principle in collisionless formation processes.« less
Authors:
 [1]
  1. Department of Astronomy and Space Science, Sejong University, 98 Gunja-dong, Gwangjin-Gu, Seoul 143-747 (Korea, Republic of)
Publication Date:
OSTI Identifier:
22365795
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 788; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANISOTROPY; ASTROPHYSICS; COMPUTERIZED SIMULATION; DENSITY; EQUILIBRIUM; GALAXIES; GALAXY CLUSTERS; MASS; NONLUMINOUS MATTER; ORBITS; PHASE SPACE; ROTATION; SPHERICAL CONFIGURATION; STARS; VELOCITY