Modeling mass independent of anisotropy

TL;DR

This paper refines the method for estimating galaxy mass within the half-light radius, demonstrating its robustness against anisotropy variations and applying it to various galaxy types, revealing a U-shaped mass-to-light ratio trend.

Contribution

It introduces a simplified, anisotropy-independent approach to determine galaxy mass within the half-light radius and applies it across different galaxy populations.

Findings

Mass within half-light radius can be reliably estimated with minimal assumptions.

Milky Way dwarf spheroidals are consistent with a ~3 x 10^9 M_sun halo mass.

Mass-to-light ratio exhibits a U-shape across galaxy types.

Abstract

By manipulating the spherical Jeans equation, Wolf et al. (2010) show that the mass enclosed within the 3D deprojected half-light radius r_1/2 can be determined with only mild assumptions about the spatial variation of the stellar velocity dispersion anisotropy as long as the projected velocity dispersion profile is fairly flat near the half-light radius, as is typically observed. They find M_1/2 = 3 \sigma_los^2 r_1/2 / G ~ 4 \sigma_los^2 R_eff / G, where \sigma_los^2 is the luminosity-weighted square of the line-of-sight velocity dispersion and R_eff is the 2D projected half-light radius. This finding can be used to show that all of the Milky Way dwarf spheroidal galaxies (MW dSphs) are consistent with having formed within a halo of mass approximately 3 x 10^9 M_sun assuming a LCDM cosmology. In addition, the dynamical I-band mass-to-light ratio (M/L) vs. M_1/2 relation for dispersion-supported galaxies follows a U-shape, with a broad minimum near M/L ~ 3 that spans dwarf elliptical galaxies to normal ellipticals, a steep rise to M/L ~ 3,200 for ultra-faint dSphs, and a more shallow rise to M/L ~ 800 for galaxy cluster spheroids.