# Constraining the Physical State of the Hot Gas Halos in NGC 4649 and NGC 5846

## TL;DR

This study compares X-ray and optical mass profiles of NGC 4649 and NGC 5846 to assess the hot gas halos' physical state, revealing mostly hydrostatic equilibrium with localized deviations linked to nuclear activity and gas sloshing.

## Contribution

It provides the first detailed joint X-ray and optical analysis of these galaxies' hot halos, highlighting the impact of non-thermal pressure and gas dynamics on mass estimates.

## Key findings

- X-ray mass profiles are smooth and consistent with optical estimates beyond 12 kpc.
- Central regions of NGC 4649 show underpredicted mass, indicating non-thermal pressure.
- NGC 5846 exhibits azimuthal asymmetries and signs of gas sloshing affecting hydrostatic equilibrium.

## Abstract

We present results of a joint \textit{Chandra}/\textit{XMM-Newton} analysis of the early-type galaxies NGC 4649 and NGC 5846 aimed at investigating differences between mass profiles derived from X-ray data and those from optical data, to probe the state of the hot ISM in these galaxies. If the hot ISM is at a given radius in hydrostatic equilibrium (HE) the X-ray data can be used to measure the total enclosed mass of the galaxy. Differences from optically-derived mass distributions therefore yield information about departures from HE in the hot halos. The X-ray mass profiles in different angular sectors of NGC 4649 are generally smooth with no significant azimuthal asymmetries within \(12\) kpc. Extrapolation of these profiles beyond this scale yields results consistent with the optical estimate. However, in the central region (\(r < 3\) kpc) the X-ray data underpredict the enclosed mass, when compared with the optical mass profiles. Consistent with previous results we estimate a non-thermal pressure component accounting for \(30\%\) of the gas pressure, likely linked to nuclear activity. In NGC 5846 the X-ray mass profiles show significant azimuthal asymmetries, especially in the NE direction. Comparison with optical mass profiles in this direction suggests significant departures from HE, consistent with bulk gas compression and decompression due to sloshing on \(\sim 15\) kpc scales; this effect disappears in the NW direction where the emission is smooth and extended. In this sector we find consistent X-ray and optical mass profiles, suggesting that the hot halo is not responding to strong non-gravitational forces.