On the patchy appearance of the circum-Galactic medium and the influence of foreground absorption

Abstract

Recent studies have demonstrated that the emission from the circumgalactic medium of the Milky Way displays a relatively high degree of patchiness on angular scales of $\sim 10^{\circ }$. Taking advantage of the Spectrum Roentgen Gamma eROSITA Final Equatorial Depth Survey (eFEDS), we aim to constrain any variation in the soft X-ray surface brightness on scales going from sub-degree to a hundred square degrees. We observe modulations of about $60$% on scales of several degrees and decreasing for higher energies. The observed patchiness is stable over a period of two years, therefore excluding that it is induced by Solar wind charge exchange. We also observe no correlation between such excess and the density of galaxies in the Local Universe, suggesting no strong contribution from the hot baryons in the filaments of the Cosmic web. Instead, the soft X-ray emission is anti-correlated with the column density of absorbing material. Indeed, we can reproduce the spectrum of the bright and dark regions by simply varying the column density of the matter absorbing the emission components located beyond the Local Hot Bubble, while no modulation of the intrinsic emission is required. At high Galactic latitudes, the eROSITA all sky map shows patchiness of the soft X-ray diffuse emission similar to the one observed in the eFEDS field, it is therefore likely that the same "absorption-modulation" is present over the entire sky. These results highlight the importance of an accurate treatment of the absorption effects, to determine the patchiness of the circumgalactic medium.

Accepted for publication in Astronomy and Astrophysics

References in corpus (18)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Gaia-2MASS 3D maps of Galactic interstellar dust within 3 kpc
• The eROSITA Final Equatorial Depth Survey (eFEDS): The X-ray catalog
• Galaxy And Mass Assembly (GAMA): Data Release 4 and the z < 0.1 total and z < 0.08 morphological galaxy stellar mass functions
• Constraining the Milky Way's Hot Gas Halo with OVII and OVII Emission Lines
• Star formation near the Sun is driven by expansion of the Local Bubble
• The gas-to-extinction ratio and the gas distribution in the Galaxy
• The Structure of the Local Hot Bubble
• The Abell 3391/95 galaxy cluster system: A 15 Mpc intergalactic medium emission filament, a warm gas bridge, infalling matter clumps, and (re-) accelerated plasma discovered by combining SRG/eROSITA data with ASKAP/EMU and DECam data
• The Circum-Galactic Medium of MASsive Spirals II: Probing the Nature of Hot Gaseous Halo around the Most Massive Isolated Spiral Galaxies
• A disk-dominated and clumpy circumgalactic medium of the Milky Way seen in X-ray emission
• The eROSITA Final Equatorial Depth Survey (eFEDS): X-ray emission around star-forming and quiescent galaxies at $0.05<z<0.3$
• Abundance and temperature of the outer hot circum-Galactic medium: The SRG/eROSITA view of the soft X-ray background in the eFEDS field
• The Heraklion Extragalactic Catalogue (HECATE): a value-added galaxy catalogue for multi-messenger astrophysics
• Detecting shocked intergalactic gas with X-ray and radio observations
• disnht: modeling X-ray absorption from distributed column densities
• The high-velocity clouds above the disk of the outer Milky Way: misty precipitating gas in a region roiled by stellar streams

Cited by in corpus (7)

• The SRG/eROSITA all-sky survey: First X-ray catalogues and data release of the western Galactic hemisphere
• Abundance and temperature of the outer hot circum-Galactic medium: The SRG/eROSITA view of the soft X-ray background in the eFEDS field
• SRG/eROSITA X-ray shadowing study of giant molecular clouds
• eROSITA narrowband maps at the energies of soft X-ray emission lines
• Cross-correlation between soft X-rays and galaxies A new benchmark for galaxy evolution models
• Soft X-ray line emission from hot gas in intervening galaxy halos and diffuse gas in the cosmic web
• Baryonic Ecosystem IN Galaxies (BEINGMgII) -- III. Cool gas reservoirs at $0.3\le z\le 1.6$ in the Dark Energy Survey