The Hot Circumgalactic Medium of the Milky Way: Evidence for Supervirial, Virial, and Subvirial Temperatures; Nonsolar Chemical Composition; and Nonthermal Line Broadening

Das, Sanskriti; Mathur, S.; Gupta, Anjali; Krongold, Y.

doi:10.3847/1538-4357/ac0e8e

Cited by 30 publications

(21 citation statements)

References 95 publications

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“…By choosing these values for Φ and cs implies rc ≈ 1 kpc (see section 2.2). This value of kT ≈ 400 eV is compatible with recent observations of the Galactic halo that presents a mixed hot-warm phase with a hot phase for which the temperature can reach ∼1 keV (Das et al 2021). It should be noted that a small increase in the gas temperature does not significantly change the critical radius and thus has little effect on the results.…”

Section: Galactic Gas Temperature and Density Profilesupporting

confidence: 91%

A galactic breeze origin for the Fermi bubbles emission

Tourmente

Rodgers-Lee

Taylor

2022

Monthly Notices of the Royal Astronomical Society

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The origin of the Fermi bubbles, which constitute two gamma-ray emitting lobes above and below the Galactic plane, remains unclear. The possibility that this Fermi bubbles gamma-ray emission originates from hadronic cosmic rays advected by a subsonic Galactic outflow, or breeze, is here explored. The simulation of a breeze solution and subsequent cosmic ray transport is carried out using the hydrodynamical code, PLUTO, in combination with a cosmic ray transport code. The Galactic outflow model obtained is found to be compatible with both inferences of the decelerating outflow velocity profile of the gas in the Fermi bubbles region, and evidence for the presence of a large amount of hot ionised gas out in the Galactic halo region. Although simple, this model is found to be able to reproduce the observed Fermi-LAT energy flux at high Galactic latitudes. Following these results a prediction concerning the gamma-ray emission for 1-3 TeV photons is made for future comparison with CTA/SWGO measurements.

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Section: Galactic Gas Temperature and Density Profilesupporting

confidence: 91%

A galactic breeze origin for the Fermi bubbles emission

Tourmente

Rodgers-Lee

Taylor

2022

Monthly Notices of the Royal Astronomical Society

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“…Our averaged spectra include an ample set of lines of sight, including many directions that do not cross these bubbles. The same was found by Das et al (2021) for Mrk 421, whose line of sight does not cross the bubbles. This is further confirmed by emission studies of the CGM, which have found a hot component coexistent with the virial phase toward directions away from the Galactic center (e.g., Bhattacharyya et al 2022;Bluem et al 2022;Gupta et al 2022).…”

Section: The Extended Hot Cgm Componentsupporting

confidence: 83%

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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“…In our analysis of NGC 253, only the central region has this hotter component, which is the likely explanation for why the S and Si peaks are so prominent in that location. Das et al (2019Das et al ( , 2021 found α-enhancement in their analysis of the Milky Way's CGM. Gupta et al (2022) also found supersolar Ne/O in the Galactic eROSITA bubbles.…”

Section: Comparison To M82 Metal Abundances and Their Distributionsmentioning

confidence: 96%

X-Ray Properties of NGC 253's Starburst-driven Outflow

López

Lopez

Nguyen

et al. 2023

ApJ

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We analyze image and spectral data from ≈365 ks of observations from the Chandra X-ray Observatory of the nearby, edge-on starburst galaxy NGC 253 to constrain properties of the hot phase of the outflow. We focus our analysis on the −1.1 to +0.63 kpc region of the outflow and define several regions for spectral extraction where we determine best-fit temperatures and metal abundances. We find that the temperatures and electron densities peak in the central ∼250 pc region of the outflow and decrease with distance. These temperature and density profiles are in disagreement with an adiabatic spherically expanding starburst wind model and suggest the presence of additional physics such as mass loading and nonspherical outflow geometry. Our derived temperatures and densities yield cooling times in the nuclear region of a few million years, which may imply that the hot gas can undergo bulk radiative cooling as it escapes along the minor axis. Our metal abundances of O, Ne, Mg, Si, S, and Fe all peak in the central region and decrease with distance along the outflow, with the exception of Ne, which maintains a flat distribution. The metal abundances indicate significant dilution outside of the starburst region. We also find estimates of the mass outflow rates, which are 2.8 M ⊙ yr−1 in the northern outflow and 3.2 M ⊙ yr−1 in the southern outflow. Additionally, we detect emission from charge exchange and find it makes a significant contribution (20%–42%) to the total broadband (0.5–7 keV) X-ray emission in the central and southern regions of the outflow.

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The Hot Circumgalactic Medium of the Milky Way: Evidence for Supervirial, Virial, and Subvirial Temperatures; Nonsolar Chemical Composition; and Nonthermal Line Broadening

Cited by 30 publications

References 95 publications

A galactic breeze origin for the Fermi bubbles emission

A galactic breeze origin for the Fermi bubbles emission

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

X-Ray Properties of NGC 253's Starburst-driven Outflow

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