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27 April 2024 |
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On the patchy appearance of the circum-Galactic medium and the influence of foreground absorption | | G. Ponti
; J. S. Sanders
; N. Locatelli
; X. Zheng
; Y. Zhang
; M. Yeung
; M. Freyberg
; K. Dennerl
; J. Comparat
; A. Merloni
; E. Di Teodoro
; M. Sasaki
; T. H. Reiprich
; | | Date: |
3 Nov 2022 | | 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 $sim10^circ$. 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. | | Source: | arXiv, 2211.02060 | | Services: | Forum | Review | PDF | Favorites | |
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