X-ray properties of massive compact relic galaxies

TL;DR

This study investigates the X-ray properties of local compact elliptical galaxies, revealing diverse hot gaseous halos and potential links to high-redshift red nuggets, thereby providing insights into early galaxy evolution.

Contribution

It presents the first detailed X-ray analysis of local compact relic galaxies, highlighting their hot gas properties and possible evolutionary connections to high-redshift red nuggets.

Findings

Two galaxies host extended X-ray atmospheres enabling thermodynamic profiling.

High-resolution spectral modeling indicates super-solar alpha/Fe ratios in MRK 1216.

Most galaxies show faint or no X-ray halos, with some displaying AGN-like emission.

Abstract

We present the X-ray analysis of seven local compact elliptical galaxies (cEGs), selected for their morphological resemblance to high-redshift red nuggets. As likely descendants of the red nugget population, cEGs offer a unique window into the early Universe, enabling the study of early galaxy evolution and the interplay between black holes, stellar bulges, and dark matter halos. Using data from Chandra and XMM-Newton, we investigate the properties of the hot gaseous halos in cEGs. Two galaxies - MRK 1216 and PGC 32873 - host luminous, spatially extended X-ray atmospheres, allowing us to derive radial thermodynamic profiles. For MRK 1216, we performed high-resolution spectral modeling with RGS data, which hints at super-solar $\alpha/\rm{Fe}$ abundance ratios. The remaining galaxies show either faint or undetected X-ray halos, though several display AGN-like (active galactic nucleus) power-law emission. In the context of local scaling relations, cEGs show only mild deviations from the general galaxy population, exhibiting a slightly steeper $M_{\star}-L_{X}$ relation and occupying the lower boundary of the $M_{\star}$-$M_{\rm vir}$ relation. These trends suggest that high-redshift red nuggets may also host a diverse range of X-ray atmospheres. We speculate that the compactness of cEGs may trace back to the population of `little red dots' (LRDs), hinting at a potential link between LRDs, red nuggets, and compact relic galaxies in the local Universe.