Mass discrepancy in galaxy clusters as a result of the offset between dark matter and baryon distributions

TL;DR

This paper investigates how offsets between the X-ray and gravitational centers in galaxy clusters can cause significant discrepancies in mass measurements, emphasizing the importance of considering these offsets in dynamical analyses.

Contribution

It provides a theoretical analysis of the dynamical effects of lensing-X-ray offsets and compares these effects with observational data, highlighting their impact on mass discrepancy.

Findings

Offsets can cause up to a factor of two difference in mass estimates

Offsets are common in lensing clusters and affect core region measurements

Ignoring offsets may lead to inaccurate dynamical mass determinations

Abstract

Recent studies of lensing clusters reveal that it might be fairly common for a galaxy cluster that the X-ray center has an obvious offset from its gravitational center which is measured by strong lensing. We argue that if these offsets exist, then X-rays and lensing are indeed measuring different regions of a cluster, and may thus naturally result in a discrepancy in the measured gravitational masses by the two different methods. Here we investigate theoretically the dynamical effects of such lensing-X-ray offsets, and compare with observational data. We find that for typical values, the offset alone can give rise to a factor of two difference between the lensing and X-ray determined masses for the core regions of a cluster, suggesting that such "offset effect" may play an important role and should not be ignored in our dynamical measurements of clusters.