Probing the Outskirts of the Early Stage Galaxy Cluster Merger A1750

TL;DR

This study investigates the outskirts of the merging galaxy cluster A1750 using X-ray and optical data, finding no evidence of gas clumping and detecting diffuse cool gas consistent with the warm-hot intergalactic medium.

Contribution

It provides the first detailed entropy and gas fraction profiles of A1750 out to the virial radius, challenging previous findings of gas clumping in cluster outskirts.

Findings

Entropy profiles align with self-similar models.

Gas fractions match cosmic mean values.

Detection of diffuse cool gas consistent with WHIM.

Abstract

We present results from recent Suzaku and Chandra X-ray, and MMT optical observations of the strongly merging "double cluster" A1750 out to its virial radius, both along and perpendicular to a putative large-scale structure filament. Some previous studies of individual clusters have found evidence for ICM entropy profiles that flatten at large cluster radii, as compared with the self-similar prediction based on purely gravitational models of hierarchical cluster formation, and gas fractions that rise above the mean cosmic value. Weakening accretion shocks and the presence of unresolved cool gas clumps, both of which are expected to correlate with large scale structure filaments, have been invoked to explain these results. In the outskirts of A1750, we find entropy profiles that are consistent with self-similar expectations, and gas fractions that are consistent with the mean cosmic value, both along and perpendicular to the putative large scale filament. Thus, we find no evidence for gas clumping in the outskirts of A1750, in either direction. This may indicate that gas clumping is less common in lower temperature (kT~4keV), less massive systems, consistent with some (but not all) previous studies of low mass clusters and groups. Cluster mass may therefore play a more important role in gas clumping than dynamical state. Finally, we find evidence for diffuse, cool (<1 keV) gas at large cluster radii (R200) along the filament, which is consistent with the expected properties of the denser, hotter phase of the WHIM.