Circumgalactic Medium on the Largest Scales: Detecting X-Ray Absorption Lines with Large-area Microcalorimeters

Abstract

The circumgalactic medium (CGM) plays a crucial role in galaxy evolution as it fuels star formation, retains metals ejected from the galaxies, and hosts gas flows in and out of galaxies. For Milky Way–type and more-massive galaxies, the bulk of the CGM is in hot phases best accessible at X-ray wavelengths. However, our understanding of the CGM remains largely unconstrained due to its tenuous nature. A promising way to probe the CGM is via X-ray absorption studies. Traditional absorption studies utilize bright background quasars, but this method probes the CGM in a pencil beam, and, due to the rarity of bright quasars, the galaxy population available for study is limited. Large-area, high spectral resolution X-ray microcalorimeters offer a new approach to exploring the CGM in emission and absorption. Here, we demonstrate that the cumulative X-ray emission from cosmic X-ray background sources can probe the CGM in absorption. We construct column density maps of major X-ray ions from the Magneticum simulation and build realistic mock images of nine galaxies to explore the detectability of X-ray absorption lines arising from the large-scale CGM. We conclude that the O VII absorption line is detectable around individual massive galaxies at the 3σ–6σ confidence level. For Milky Way–type galaxies, the O VII and O VIII absorption lines are detectable at the ∼ 6σ and ∼ 3σ levels even beyond the virial radius when coadding data from multiple galaxies. This approach complements emission studies, does not require additional exposures, and will allow for probing the baryon budget and the CGM at the largest scales.

Properties of the Line-of-sight Velocity Field in the Hot and X-Ray-emitting Circumgalactic Medium of Nearby Simulated Disk Galaxies

“…Nelson et al (2023a) investigated the possibility that the resonant scattering of O VIIr emission line photons could boost the CGM signal from this line to be significantly brighter than the intrinsic emission alone, using galaxies from the the Illustris TNG50-1 (hereafter TNG50) simulations. Bogdan et al (2023) showed using mock LEM observations of galaxies from the Magneticum simulations that O VII and O VIII absorption lines can be detected at very large radius. Comparisons between galaxies from Illustris "The Next Generation" (TNG), SIMBA, and EAGLE demonstrate that emission lines from oxygen and iron in the X-ray band can be used to distinguish between different models of AGN feedback and determine the role of feedback from supernovae and black holes in regulating star formation (Truong et al 2023b).…”