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26 April 2024 |
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Abundance and temperature of the outer hot circum-Galactic medium: The SRG/eROSITA view of the soft X-ray background in the eFEDS field | | G. Ponti
; X. Zheng
; N. Locatelli
; S. Bianchi
; Y. Zhang
; K. Anastasopoulou
; J. Comparat
; K. Dennerl
; M. Freyberg
; F. Haberl
; A. Merloni
; T. H. Reiprich
; M. Salvato
; J. Sanders
; M. Sasaki
; A. Strong
; M. C. H. Yeung
; | | Date: |
6 Oct 2022 | | Abstract: | Despite their vital importance to understand galaxy evolution and our own
Galactic ecosystem, our knowledge of the physical properties of the hot phase
of the Milky Way is still inadequate. However, sensitive SRG/eROSITA large area
surveys are now providing us with the long sought-after data needed to mend
this state of affairs. We present the properties of the soft X-ray emission as
observed by eROSITA in the eFEDS field. We measure the temperature and metal
abundance of the hot circum-Galactic medium (CGM) to be within
$kT_{CGM}=0.153-0.178$ keV and $Z_{CGM}=0.052-0.072$ $Z_odot$, depending on
the contribution of solar wind charge exchange (SWCX). Slightly larger CGM
abundances $Z_{CGM}=0.05-0.10$ $Z_odot$ are possible, considering the
uncertain extrapolation of the extragalactic Cosmic X-ray background (CXB)
emission below $sim1$ keV. To recover CGM abundances as large as $Z_{CGM}=0.3$
$Z_odot$, it must be postulated the presence of an additional component,
likely associated with the warm-hot intergalactic medium, providing
$sim15-20$% of the flux in the soft X-ray band. The emission in the soft band
is dominated by the CGM, with contributions from the CXB and the local hot
bubble. Moreover, the eROSITA data require the presence of an additional
component associated with the elusive Galactic corona plus a possible
contribution from unresolved M dwarf stars. This component has a temperature of
$kTsim0.4-0.7$ keV and it might be out of thermal equilibrium. It contributes
$sim9$% to the total emission in the 0.6--2 keV band, therefore it is a likely
candidate to produce part of the unresolved CXB flux observed in X-ray
ultra-deep fields. We also observe a significant contribution to the soft X-ray
flux due to SWCX, during periods characterised by stronger solar wind activity,
and causing the largest uncertainty on the determination of the CGM
temperature. | | Source: | arXiv, 2210.03133 | | Services: | Forum | Review | PDF | Favorites | |
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