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