Cooling in the X-ray halo of the rotating, massive early-type galaxy NGC 7049

TL;DR

This study analyzes X-ray data of galaxy NGC 7049, revealing how rotation influences hot gas cooling and multiphase structure, leading to a disc formation consistent with hydrodynamical simulations.

Contribution

It provides observational evidence that galaxy rotation affects hot gas cooling and condensation, supporting models predicting multiphase disc formation in rotating galaxies.

Findings

Hot gas shows multi-temperature structure indicating ongoing cooling.

Rotational support alters multiphase condensation regardless of cooling time ratios.

Condensing gas follows non-radial orbits forming a disc, matching simulations.

Abstract

The relative importance of the physical processes shaping the thermodynamics of the hot gas permeating rotating, massive early-type galaxies is expected to be different from that in non-rotating systems. Here, we report the results of the analysis of XMM-Newton data for the massive, lenticular galaxy NGC 7049. The galaxy harbours a dusty disc of cool gas and is surrounded by an extended hot X-ray emitting gaseous atmosphere with unusually high central entropy. The hot gas in the plane of rotation of the cool dusty disc has a multi-temperature structure, consistent with ongoing cooling. We conclude that the rotational support of the hot gas is likely capable of altering the multiphase condensation regardless of the $t_{\rm cool}/t_{\rm ff}$ ratio, which is here relatively high, $\sim 40$. However, the measured ratio of cooling time and eddy turnover time around unity ($C$-ratio $\approx 1$) implies significant condensation, and at the same time, the constrained ratio of rotational velocity and the velocity dispersion (turbulent Taylor number) ${\rm Ta_t} > 1$ indicates that the condensing gas should follow non-radial orbits forming a disc instead of filaments. This is in agreement with hydrodynamical simulations of massive rotating galaxies predicting a similarly extended multiphase disc.