Ruminations Upon the Modeling of X-ray Foregrounds, Backgrounds and Faint Sources

TL;DR

This paper develops a forward modeling strategy to accurately extract faint X-ray signals from galaxy clusters by modeling all foregrounds and backgrounds, improving analysis of current and future X-ray observations.

Contribution

It introduces a comprehensive forward modeling approach for X-ray foregrounds and backgrounds, enabling better analysis of faint, diffuse sources in galaxy cluster observations.

Findings

Modest improvement for bright clusters at intermediate redshifts.

Significant advantages for high-redshift, low-surface-brightness clusters.

Provides a correction for Chandra ACIS detector miscalibration.

Abstract

With the goal of extracting as much information as possible from Chandra and XMM-Newton observations of faint, diffuse sources such as galaxy clusters, as well as those of future X-ray telescopes, we present a strategy for forward modeling all the foreground and background signals present in these data. This work leverages widespread efforts to understand the soft X-ray emission from the Galaxy, as well as the cosmic X-ray background and instrument-specific, particle-induced backgrounds. Statistically, a forward model of the foregrounds and backgrounds is preferable to alternatives because it requires no binning of the data, and allows straightforward marginalization over systematic uncertainties. We apply these methods to several galaxy clusters at intermediate-to-high redshifts, spanning a range of masses and morphologies, using Chandra and/or XMM-Newton data. Our results suggest a modest improvement even for relatively bright clusters at these redshifts, and more substantial advantages in the high-redshift, low-surface-brightness regime. We also discuss and provide a simple correction for a time-dependent miscalibration of the Chandra ACIS detectors identified in archival galaxy cluster data.