Probing the anisotropy of the Milky Way gaseous halo: Sight-lines toward Mrk 421 and PKS2155-304

Abstract

(Abridged) We recently found that the halo of the Milky Way contains a large reservoir of warm-hot gas that contains a large fraction of the missing baryons from the Galaxy. The average physical properties of this circumgalactic medium (CGM) are determined by combining average absorption and emission measurements along several extragalactic sightlines. However, there is a wide distribution of both, the halo emission measure and the \ovii column density, suggesting that the Galactic warm-hot gaseous halo is anisotropic. We present {\it Suzaku} observations of fields close to two sightlines along which we have precise \ovii absorption measurements with \chandran. The column densities along these two sightlines are similar within errors, but we find that the emission measures are different. Therefore the densities and pathlengths in the two directions must be different, providing a suggestive evidence that the warm-hot gas in the CGM of the Milky Way is not distributed uniformly. However, the formal errors on derived parameters are too large to make such a claim. The average density and pathlength of the two sightlines are similar to the global averages, so the halo mass is still huge, over 10 billion solar masses. With more such studies, we will be able to better characterize the CGM anisotropy and measure its mass more accurately. We also show that the Galactic disk makes insignificant contribution to the observed \ovii absorption; a similar conclusion was also reached independently about the emission measure. We further argue that any density inhomogeneity in the warm-hot gas, be it from clumping, from the disk, or from a non-constant density gradient, would strengthen our result in that the Galactic halo path-length and the mass would become larger than what we estimate here. As such, our results are conservative and robust.

27 pages, 5 figures, submitted to ApJ

References in corpus (9)

• The Search for the Missing Baryons at Low Redshift
• X-Ray Absorption from the Milky Way Halo and the Local Group
• Where are the ``Missing'' Galactic Baryons?
• An XMM-Newton Survey of the Soft X-ray Background. III. The Galactic Halo X-ray Emission
• X-ray and UV spectroscopy of Galactic diffuse hot gas along the LMC X--3 sight line
• Chandra and Far Ultraviolet Spectroscopic Explorer Observations of z~0 Warm-Hot Gas Toward PKS 2155-304
• Warm-hot gas in groups and galaxies toward H2356-309
• On the nature of the z=0 X-ray absorbers: I. Clues from an external group
• The warm-hot gaseous halo of the Milky Way

Cited by in corpus (29)

• The Extended Distribution of Baryons Around Galaxies
• Evidence for a Massive, Extended Circumgalactic Medium Around the Andromeda Galaxy
• The Magellanic Stream System: I. Ram-pressure tails and the relics of the collision between the Magellanic Clouds
• Project AMIGA: The Circumgalactic Medium of Andromeda
• XMM-Newton Survey of Local O VII Absorption Lines in the Spectra of Active Galactic Nuclei
• Multiple temperature components of the hot circumgalactic medium of the Milky Way
• The hot circumgalactic medium of the Milky Way: evidence for super-virial, virial, and sub-virial temperature, non-solar chemical composition, and non-thermal line broadening
• Super-virial temperature or Neon overabundance?: Suzaku observations of the Milky Way circumgalactic Medium
• Widespread Detection of Two Components in the Hot Circumgalactic Medium of the Milky Way
• The Hot, Accreted Halo of NGC 891
• Probing the Anisotropy of the Milky Way Gaseous Halo-II: sightline toward Mrk509
• Evidence for massive warm-hot circumgalactic medium around NGC 3221
• High Resolution X-ray Spectroscopy of the Local Hot Gas along the 3C 273 Sightline
• EAGLE-Auriga: effects of different subgrid models on the baryon cycle around Milky Way-mass galaxies
• GARROTXA Cosmological Simulations of Milky Way-sized Galaxies: General Properties, Hot Gas Distribution, and Missing Baryons
• The warm-hot, extended, massive circumgalactic medium of NGC 3221: an XMM-Newton discovery
• The warm-hot circumgalactic medium around EAGLE-simulation galaxies and its detection prospects with X-ray line emission
• The hot circumgalactic medium of the Milky-Way: new insights from XMM-Newton observations
• Structual Study of Galactic Hot Gas toward Markarian 421 from X-Ray Absorption and Emission Lines
• Empirical estimates of the Galactic halo contribution to the dispersion measures of extragalactic fast radio bursts using X-ray absorption
• Agnostic Stacking of Intergalactic Doublet Absorption: Measuring the NeVIII Population
• Probing the hot circumgalactic medium of external galaxies in X-ray absorption II: a luminous spiral galaxy at $z\approx 0.225$
• Diagnostics of Gaseous Halo of the Milky Way by a Shock Wave from the Galactic Centre
• Probing the Warm-Hot Circumgalactic Medium with broad OVI and X-rays
• The Origin of the X-ray Emission from the High-velocity Cloud MS30.7-81.4-118
• Is the Milky Way's Hot Halo Convectively Unstable?
• A High Signal-to-Noise HST Spectrum Toward J1009+0713: Precise Absorption Measurements in the CGM of Two Galaxies
• On the origin of the $10^7$ K hot emitting gas in the Circumgalactic medium of the Milky Way
• Point source contribution to the Diffuse X-ray Background below 1 keV and its effect on our understanding of the circum-galactic medium