Robust detection of hot intragroup medium in optically selected, poor galaxy groups by eROSITA

TL;DR

This study robustly detects hot intragroup medium in optically selected poor galaxy groups using eROSITA X-ray data, revealing its presence but insufficient to solve the missing baryons problem.

Contribution

First robust detection of hot intragroup medium in poor galaxy groups through stacked eROSITA X-ray images, expanding understanding of baryon content in these structures.

Findings

Hot intragroup medium detected in poor galaxy groups.

The gas is insufficient to account for the universal baryon fraction.

The missing baryons problem persists in poor galaxy groups.

Abstract

Over the last several decades, extensive research has been conducted on the baryon cycles within cosmic structures, encompassing a broad mass range from dwarf galaxies to galaxy clusters. However, a notable gap in understanding the cosmic baryon cycle is the poor galaxy groups with halo masses around $10^{13}\ M_{\odot}$ (e.g., McGaugh et al. 2010). Poor galaxy groups, like our own Local Group, are prevalent throughout the universe, yet robust detection of their hot, X-ray emitting intragroup medium (IGrM) has remained elusive. The presence of this hot IGrM is crucial for addressing the long-standing "missing baryons" problem. Previous ROSAT-based studies were limited by a small number of X-ray bright samples, thus restricting the scope of their findings. Here we show a robust detection of this hot IGrM in a large, optically selected poor groups sample, based on the stacked X-ray images from the eROSITA Final Equatorial Depth Survey. These groups are identified in DESI LS with a mass range of log($M_\mathrm{halo}/h^{-1}M_{\odot}$) = 11.5-13.5 and a redshift range of z = 0.1-0.5. Additionally, our results indicate that despite its presence in virtually groups at all sizes, this gas component is still not sufficient to recover the universal baryon fraction, and hence the "missing baryons" problem still persists in poor galaxy groups.