Probing the Circumgalactic Medium with X-Ray Absorption Lines

Mathur, S.

doi:10.1007/978-981-16-4544-0_112-1

Cited by 8 publications

(6 citation statements)

References 89 publications

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“…This particular phase had been linked to the coronal gas of the Milky Way (MW) that should exist at the virial temperature of the dark matter halo (Spitzer 1956). The detection of a component with temperatures of ∼10 6 K (∼0.2 keV) in emission (Snowden et al 2000;Yao et al 2009;Yoshino et al 2009;Henley et al 2010;Henley & Shelton 2013;Henley et al 2015;Nakashima et al 2018) and absorption (Gupta et al 2012;Nicastro et al 2016;Gupta et al 2017;Gatuzz & Churazov 2018;Mathur 2022) has fulfilled this prediction, and has consequently been named as the virial or the warm-hot component of the CGM.…”

Section: Introductionmentioning

confidence: 95%

The Hot Circumgalactic Medium of the Milky Way: New Insights from XMM-Newton Observations

Bhattacharyya

Das

Gupta

et al. 2023

ApJ

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We present XMM-Newton observations around the sight line of Mrk 421. The emission spectrum of the Milky Way (MW) circumgalactic medium (CGM) shows that a two-phase model is a better fit to the data compared to a single-phase model; in addition to the warm-hot virial phase at log (T/K) = 6.30 ± 0.02, a hot super-virial phase at log (T/K) = 6.88 − 0.06 + 0.07 is required. Furthermore, we present observations of five fields within 5 degrees of the primary field. Their spectra also require a two-phase model at warm-hot and hot temperatures. The hot phase, which was first discovered in Das et al. in 2019, appears to be widespread. By chemical tagging, we show that the emission from the supevirial phase comes from the L-shell transitions of Fe xviii–Fe xxii, and that the range of temperatures probed in emission is distinct from that in absorption. We detect scatter in temperature and emission measure in both the phases, and deduce that there is small-scale density inhomogeneity in the MW CGM. The emitting gas likely has higher density, possibly from regions close to the disk of the MW, while the absorption in the virial phase may arise from low-density gas extended out to the virial radius of the MW. The presence of the super-virial phase far from the regions around the Galactic center implicates physical processes unrelated to the activity at the Galactic center. Hot outflows resulting from star formation activity throughout the Galactic disk are likely to be responsible for producing this phase.

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Section: Introductionmentioning

confidence: 95%

The Hot Circumgalactic Medium of the Milky Way: New Insights from XMM-Newton Observations

Bhattacharyya

Das

Gupta

et al. 2023

ApJ

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“…This warm-hot 10 6 K gas is observed using the emission and absorption lines of He-like and H-like metal ions, e.g., O VII and O VIII, and free-free continuum emission in X-ray. However, due to the intrinsic difficulties in detecting the warm-hot gas, the warm-hot CGM has been best characterized for the Milky Way (see the review by Mathur 2022).…”

Section: Introductionmentioning

confidence: 99%

Detecting the Effect of Nonthermal Sources on the Warm-hot Galactic Halo

Das

2024

ApJL

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We report the first detection of nonthermal broadening of O vii lines in the warm-hot ≈106 K circumgalactic medium of the Milky Way. We use z = 0 absorption of O vii Kα, O vii Kβ, and O viii Kα lines in archival grating data of b > 15° quasar sightlines from Chandra and XMM-Newton. Nonthermal line broadening is evident in two-thirds of the sightlines considered, and on average is constrained at 4.6σ significance. Nonthermal line broadening dominates over thermal broadening. We extensively test whether the appearance of nonthermal line broadening could instead be because of multiple thermally broadened velocity components and robustly rule it out. Nonthermal line broadening is more evident toward sightlines at lower galactic latitude indicating the Galactic disk origin of the nonthermal sources. There is weak/no correlation between nonthermal line broadening and the angular separation of sightlines from the Galactic center, indicating that the nuclear region might not be a major source of nonthermal factors.

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“…Hence, a common way of studying it is by viewing it in absorption against bright background sources such as quasars or blazars (Tumlinson et al 2017). This method allows the detection of faint signals from absorption lines on their spectra (e.g., Mathur 2022). Gupta et al (2012) investigated the absorption lines of O VII and O VIII in the CGM of our Galaxy, by measuring the column densities from the Kα and Kβ transitions to derive properties of the hot gas around the Galaxy.…”

Section: Introductionmentioning

confidence: 99%

Detection of a Supervirial Hot Component in the Milky Way Circumgalactic Medium Along Multiple Sight Lines by Using the Stacking Technique

Lara-DI

Mathur

Krongold

et al. 2023

ApJ

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The study of the elusive hot component (T ≳ 107 K) of the Milky Way circumgalactic medium (CGM) is a novel topic for understanding Galactic formation and evolution. In this work, we use the stacking technique through 46 lines of sight with Chandra ACIS-S HETG totaling over 10 Ms of exposure time and nine lines of sight with ACIS-S LETG observations totaling over 1 Ms of exposure time, to study in absorption the presence of highly ionized metals arising from the supervirial temperature phase of the CGM. Focusing in the spectral range 4–8 Å, we were able to confirm the presence of this hot phase with high significance. We detected transitions of Si XIV K α (with a total significance of 6.0σ) and, for the first time, S XVI K α (total significance of 4.8σ) in the rest frame of our own galaxy. For S XVI K α we found a column density of 1.50 − 0.38 + 0.44 × 10 16 cm − 2 . For Si XIV K α we measured a column density of 0.87 ± 0.16 × 1016 cm−2. The lines of sight used in this work are spread across the sky, probing widely separated regions of the CGM. Therefore, our results indicate that this newly discovered hot medium extends throughout the halo and is not related only to the Galactic bubbles. The hot gas location, distribution, and covering factor, however, remain unknown. This component might contribute significantly to the missing baryons and metals in the Milky Way.

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Probing the Circumgalactic Medium with X-Ray Absorption Lines

Cited by 8 publications

References 89 publications

The Hot Circumgalactic Medium of the Milky Way: New Insights from XMM-Newton Observations

The Hot Circumgalactic Medium of the Milky Way: New Insights from XMM-Newton Observations

Detecting the Effect of Nonthermal Sources on the Warm-hot Galactic Halo

Detection of a Supervirial Hot Component in the Milky Way Circumgalactic Medium Along Multiple Sight Lines by Using the Stacking Technique

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