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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 of 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 for 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 advanced CCD imaging spectrometer detectors identified in archival galaxy cluster data.

We present imaging and spectroscopic analyses of Chandra and XMM-Newton observations of ACT-CL J0123.5−0428, one of the most massive, highest-redshift galaxy clusters detected within the survey fields of the Atacama Cosmology Telescope. The Chandra data are sufficient to characterize the morphology of this cluster and constrain the geometrically deprojected temperature in two spatial bins out to r2500, revealing a dynamically relaxed system whose temperature drops to kT = 1.8 ± 0.6 keV in the inner ∼40 kpc. Within this same inner radius, the surface brightness and density of the intracluster medium are sharply peaked, and the cooling time falls to tcool=280−120+150 Myr. A novel forward-modeling analysis of the XMM data extends imaging and spectroscopic measurements of this system out to r500, constraining the redshift to z = 1.50 ± 0.03, with a mean temperature of kT = 7.3 ± 1.1 keV and an emission-weighted mean metallicity of Z/Z⊙=0.43−0.25+0.46 . We also utilize the limited optical–IR photometric coverage of the cluster to characterize the properties of the brightest cluster galaxy (BCG), which is coincident with the X-ray peak. Despite the high redshift and strong cool core, the BCG exhibits no signs of recent or ongoing star formation, suggesting active galactic nucleus feedback has been acting persistently to stem star formation since z ∼ 2.5. These measurements identify ACT-CL J0123.5−0428 as the highest-redshift, dynamically relaxed, cool core galaxy cluster discovered to date, making it a premier target for future astrophysical and cosmological studies.

We present an in-depth Chandra X-ray analysis of the galaxy cluster SPT-CL J0417−4748 (hereafter SPT J0417) at z = 0.58 with a focus on its thermodynamic properties and the apparent absence of central star formation. Utilizing a total Chandra exposure of 103 ks, we find that the large-scale X-ray morphology is consistent with a dynamically relaxed cool-core system. The intracluster medium shows a central density of 0.08 ± 0.01 cm−3, a central pseudoentropy of 26−5+6keVcm2 , and a central cooling time of 515−75+96 Myr, values typical of massive cool-core clusters. Despite these conditions, no evidence of recent or ongoing star formation is detected in the brightest cluster galaxy (BCG). Spectral energy distribution fitting of Dark Energy Survey photometry indicates that the bulk of the stellar population formed at z ∼ 1.25, with no significant star formation over the past ∼3 Gyr, while optical spectra from Magellan show no [O II] emission. Complementary ASKAP radio and Spitzer infrared data indicate a lack of strong current active galactic nucleus (AGN) activity in the BCG. SPT J0417 exemplifies massive, relaxed cool-core clusters in which cooling and star formation appear almost completely quenched, providing valuable insights into how AGN feedback regulates the long-term thermal balance of the intracluster medium.

Galaxy clusters serve as a unique and valuable laboratory for probing cosmological models and understanding astrophysics at the high-mass limit of structure formation. Clusters that are dynamically relaxed are especially useful targets of study because of their morphological and dynamical simplicity. However, at redshifts z > 1, very few such clusters have been identified. We present results from new Chandra observations of the cluster SPT-CL J2215-3537 (hereafter SPT J2215), at z = 1.16, the second-most distant, relaxed, cool-core cluster identified to date. We place constraints on the cluster’s total mass profile and investigate its thermodynamic profiles, scaling relations (gas mass, average temperature, and X-ray luminosity), and metal enrichment, resolving the cool core and providing essential context for the massive starburst seen in its central galaxy. We contextualize the thermodynamic and cosmological properties of the cluster within a sample of well-studied, lower-redshift relaxed systems. In this way, SPT J2215 serves as a powerful high-redshift benchmark for understanding the formation of cool cores and the evolution of massive clusters of galaxies.

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.

Galaxy clusters serve as a unique and valuable laboratory for probing cosmological models and understanding astrophysics at the high-mass limit of structure formation. Clusters that are dynamically relaxed are especially useful targets of study because of their morphological and dynamical simplicity. However, at redshifts z > 1, very few such clusters have been identified. We present results from new Chandra observations of the cluster SPT-CL J2215-3537 (hereafter SPT J2215), at z = 1.16, the second most distant relaxed, cool-core cluster identified to date. We place constraints on the cluster's total mass profile and investigate its thermodynamic profiles, scaling relations (gas mass, average temperature, and X-ray luminosity), and metal enrichment, resolving the cool core and providing essential context for the massive starburst seen in its central galaxy. We contextualize the thermodynamic and cosmological properties of the cluster within a sample of well-studied, lower-redshift relaxed systems. In this way, SPT J2215 serves as a powerful high-redshift benchmark for understanding the formation of cool cores and the evolution of massive clusters of galaxies.

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.

We present an in-depth Chandra X-ray analysis of the galaxy cluster SPT-CL J0417\\(-\\)4748 (hereafter SPT J0417), at z = 0.58, with a focus on its thermodynamic properties and the apparent absence of central star formation. Utilizing a total Chandra exposure of 103 ks, we find that the large-scale X-ray morphology is consistent with a dynamically relaxed, cool-core system. The intracluster medium (ICM) shows a central density of 0.08+/-0.01 cm^-3, a central pseudo-entropy of 26^+6_-5 keVcm^2 and a central cooling time of 515^+96_-75 Myr, values typical of massive cool-core clusters. Despite these conditions, no evidence of recent or ongoing star formation is detected in the brightest cluster galaxy (BCG). Spectral energy distribution (SED) fitting of DES photometry indicates that the bulk of the stellar population formed at z~1.25, with no significant star formation over the past ~3 Gyr, while optical spectra from Magellan show no [O II] emission. Complementary ASKAP radio and Spitzer infrared data indicate a lack of strong current AGN activity in the BCG. SPT J0417 exemplifies massive, relaxed, cool-core clusters in which cooling and star formation appear almost completely quenched, providing valuable insights into how AGN feedback regulates the long-term thermal balance of the intracluster medium.

We present imaging and spectroscopic analyses of Chandra and XMM-Newton observations of ACT-CL J0123.5\\(-\\)0428, one of the most massive, highest redshift galaxy clusters detected within the survey fields of the Atacama Cosmology Telescope. The Chandra data are sufficient to characterize the morphology of this cluster and constrain the geometrically deprojected temperature in 2 spatial bins out to \\(r_2500\\), revealing a dynamically relaxed system whose temperature drops to \\(kT = 1.80.6\\) keV in the inner \\(40\\)kpc. Within this same inner radius, the surface brightness and density of the ICM is sharply peaked, and the cooling time falls to \\(t_cool=280^+150_-120\\) Myr. A novel forward-modeling analysis of the XMM data extends imaging and spectroscopic measurements of this system out to \\(r_500\\), constraining the redshift to \\(z=1.500.03\\), with a mean temperature of \\(kT = 7.31.1\\) keV and an emission-weighted mean metallicity of \\(Z/Z_ = 0.43^+0.46_-0.25\\). We also utilize the limited optical/IR photometric coverage of the cluster to characterize the properties of the brightest cluster galaxy (BCG), which is coincident with the X-ray peak. Despite the high redshift and strong cool core, the BCG exhibits no signs of recent or ongoing star formation, suggesting AGN feedback has been acting persistently to stem star formation since \\(z 2.5\\). These measurements identify ACT-CL J0123.5\\(-\\)0428 as the highest redshift, dynamically relaxed, cool core galaxy cluster discovered to date, making it a premier target for future astrophysical and cosmological studies.

The Advanced X-ray Imaging Satellite (AXIS) is one of two candidate mission concepts selected for Phase-A study for the new NASA Astrophysics Probe Explorer (APEX) mission class, with a planned launch in 2032. The X-ray camera for AXIS is under joint development by the X-ray Astronomy and Observational Cosmology (XOC) Group at Stanford, the MIT Kavli Institute (MKI), and MIT Lincoln Laboratory (MIT-LL). To accelerate development efforts and meet the AXIS mission requirements, XOC has developed a twin beamline testing system, capable of providing the necessary performance, flexibility, and robustness. We present design details, simulations, and performance results for the newer of the two beamlines, constructed and optimized to test and characterize the first full-size MIT-LL AXIS prototype detectors, operating with the Stanford-developed Multi-Channel Readout Chip (MCRC) integrated readout electronics system. The XOC X-ray beamline design is forward-looking and flexible, with a modular structure adaptable to a wide range of detector technologies identified by the Great Observatories Maturation Program (GOMAP) that span the X-ray to near-infrared wavelengths.