Temperature and Metallicity Gradients in the Hot Gas Outflows of M82
  We utilize deep Chandra X-ray Observatory imaging and spectra of M82, the
prototype of a starbursting galaxy with a multiphase wind, to map the hot
plasma properties along the minor axis of the galaxy. We extract spectra from
11 regions up to 2.5 kpc from the starbursting midplane and model the data as a
multi-temperature, optically thin thermal plasma with contributions from a
non-thermal (power-law) component and from charge exchange (CX). We examine the
gradients in best-fit parameters, including the intrinsic column density,
plasma temperature, metal abundances, and number density of the hot gas as a
function of distance from the M82 nucleus. We find that the temperatures and
number densities of the warm-hot and hot plasma peak at the starbursting ridge
and decreases along the minor axis. The temperature and density profiles are
inconsistent with spherical adiabatic expansion of a super-heated wind and
suggest mass loading and mixing of the hot phase with colder material.
Non-thermal emission is detected in all of the regions considered, and CX
comprises 8-25% of the total absorption-corrected, broad-band (0.5-7 keV) X-ray
flux. We show that the abundances of O, Ne, Mg, and Fe are roughly constant
across the regions considered, while Si and S peak within 500 pc of the central
starburst. These findings support a direct connection between the M82 superwind
and the warm-hot, metal-rich circumgalactic medium (CGM).
