Probing the hot circumgalactic medium of external galaxies in X-ray absorption II: a luminous spiral galaxy at $z\approx 0.225$

Abstract

The circumgalactic medium (CGM) is the most massive baryonic component of a spiral galaxy, shock heated to about $10^6$K for an ${\mathrm{L}}^{\star }$ galaxy. The CGM of the Milky Way has been well-characterized through X-ray absorption line spectroscopy. However, the paucity of bright background sources makes it challenging to probe the CGM of external galaxies. Previously, using broad OVI absorption as a signpost, we successfully detected the CGM of one galaxy in X-rays. Here we report on the detection of the OVII $K\alpha$ absorption line at the redshift of a spiral galaxy at $z\approx 0.225$ using 1.2 Ms of Chandra observations. This is a robust detection, clearly showing the presence of the hot gas. The mass in the hot phase is at least an order of magnitude larger than that in the cooler phases detected in the UV. The presence of hot gas $116h^{-1}$kpc from the center of this galaxy provides credence to the existence of the extended CGM of the Milky Way. There has been a report of the detection of OVII absorption from the warm-hot intergalactic medium in this sightline using stacking analysis on an older dataset. We argue that the absorption line is from the CGM of the $z\approx 0.225$ galaxy instead.

To be published in MNRAS Letters

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• The Cosmic Baryon Partition between the IGM and CGM in the SIMBA Simulations
• Quantifying Observational Projection Effects with a Simulation-based hot CGM model
• A Sub-solar Fe/O, logT~7.5 Gas Component Permeating the Milky Way's CGM
• Retrieving the hot circumgalactic medium physics from the X-ray radial profile from eROSITA with an IlustrisTNG-based forward model
• An Observationally Driven Multifield Approach for Probing the Circum-Galactic Medium with Convolutional Neural Networks