Hot gas in groups: NGC 5328 and the intriguing case of NGC 4756 with XMM-Newton

TL;DR

This study analyzes the hot gas properties in the halos of NGC 5328 and NGC 4756 using XMM-Newton data, revealing extended emissions, potential connections between structures, and insights into their evolutionary stages.

Contribution

It provides a detailed separation of X-ray emissions in complex environments and combines observations with simulations to understand galaxy evolution.

Findings

NGC 4756's hot gas extends up to 40 kpc with a luminosity of ~10^41 erg/s.

Detected gas between NGC 4756 and its substructure suggests a physical connection.

NGC 5328's hot gas extends to 110 kpc, with a similar luminosity, indicating different evolutionary stages.

Abstract

[Abridged] NGC 5238 and NGC 4756 are the brightest unperturbed elliptical galaxies in their respective loose groups. In the present study we aim at characterizing the properties of the hot gas in the halos of the brightest members and in the environment. In NGC 4756 we are also interested in the properties of a substructure identified to the SW and the region connecting the two structures, to search for a physical connection between the two. However, we have to take into account the fact that the group is projected against the bright, X-ray emitting cluster A1361, which heavily contaminates and confuses the emission from the foreground structure. We present a careful analysis of XMM-Newton data of the groups to separate different components. We also present a re-evaluation of the dynamical properties of the systems and . SPH simulations to interpret the results. We find that the X-ray source associated with NGC 4756 indeed sits on top of extended emission from the background cluster A1361, but can be relatively well distinguished from it as a significant excess over it out to r\sim150"\ (~40 kpc). NGC 4756 has an X-ray luminosity of ~10^41 erg/s due to hot gas, with an average temperature of kT\sim0.7 keV. We measure a faint diffuse emission also in the region of the subclump to the SW, but more interestingly, we detect gas between the two structures, indicating a possible physical connection. The X-ray emission from NGC 5328 is clearly peaked on the galaxy, also at 10^41 erg/s, and extends to r\sim110 kpc. Simulations provide an excellent reproduction of the SED and the global properties of both galaxies, which are caught at two different epochs of the same evolutionary process, with NGC 5328 ~2.5 Gyr younger than NGC 4756.