The MASSIVE Survey IV.: The X-ray halos of the most massive early-type galaxies in the nearby Universe

TL;DR

This study analyzes the hot X-ray gas properties of 33 early-type galaxies from the MASSIVE survey, revealing a universal L_X~T_gas^4.5 scaling law and insights into the origins and heating of the gas.

Contribution

It presents the first combined analysis of MASSIVE and ATLAS^3D galaxies, establishing a universal X-ray scaling law and examining the factors influencing hot gas properties in early-type galaxies.

Findings

All early-type galaxies follow a universal L_X~T_gas^4.5 relation.

X-ray measurements are unaffected by environment when using consistent apertures.

T_gas correlates with galaxy potential, indicating internal processes dominate gas heating.

Abstract

Studies of the physical properties of local elliptical galaxies (e.g., gas temperatures, halo masses, stellar kinematics) are shedding new light on galaxy formation. Here we present the hot X-ray gas properties of 33 early-type systems within the MASSIVE galaxy survey sample that have archival Chandra X-ray observations. Through careful X-ray spectral modeling, we derive X-ray luminosities (L_X) and plasma temperatures (T_gas) for the diffuse gas components in these galaxies. We combine the MASSIVE sample with 41 galaxies from the ATLAS^3D survey to investigate the X-ray and optical properties of a statistically significant sample of nearby early-type galaxies across a wide-range of environments. We deduce that all early-type galaxies (independent of galaxy mass and rotational support) follow a universal scaling law such that L_X~T_gas^4.5. When X-ray measurements are performed consistently in apertures set by the galaxy stellar content, the wide-scale environment does not contribute to the intrinsic scatter (~0.5dex) within the scaling relation. We further demonstrate that the scatter in L_X around both K-band luminosity (L_K) and the galaxy stellar velocity dispersion is primarily driven by T_gas, with no clear trends with halo mass, radio power, or angular momentum of the stars. It is not trivial to tie the origin of the gas directly to either the stellar mass or the galaxy potential. Indeed, our data require a steeper relation between L_X, L_K, and sigma_e than predicted by standard mass-loss models. Finally, we find a statistically significant correlation between sigma_e and T_gas, suggesting that T_gas is set by the galaxy potential inside the optical effective radius. We conclude that within the inner-most 10-30kpc region, early-types maintain pressure-supported hot gas, with a minimum T_gas set by the virial temperature, but the majority show evidence for some additional heating.