eROSITA narrowband maps at the energies of soft X-ray emission lines
arxiv(2024)
摘要
[abridged] Hot plasma plays a crucial role in regulating the baryon cycle
within the Milky Way, flowing from the energetic sources in the Galactic center
and disc, to the corona and the halo Taking advantage of the Spectrum Roentgen
Gamma (SRG)/eROSITA first all-sky survey, in this work we aim to provide a
panoramic view of the hot circumgalactic medium (CGM) of the Milky Way. The
energy resolution of eROSITA enables us to map, for the first time, the sky
within the narrow energy bands characteristic of soft X-ray emission lines. We
present the eROSITA eRASS1 half sky maps in narrow energy bands corresponding
to the most prominent soft X-ray lines: O VII and O VIII, which allow us to
constrain the distribution of the hot plasma within and surrounding the Milky
Way. We removed the expected contribution associated with the cosmic X-ray
background, the time-variable solar wind charge exchange, the local hot bubble
and foreground absorption. We use the line ratio of the oxygen lines as a proxy
to constrain the temperature of the warm-hot CGM and we define a
pseudo-temperature 𝒯 map. The map highlights how different regions
are dominated by different thermal components. Towards the outer halo, the
temperature distribution of the CGM is consistent with being constant (Δ𝒯 / ⟨𝒯⟩) ≤ 4%) on angular scales of 2-20
deg, while significant variations ∼ 12% are observed on many tens of
degrees scales, when comparing the northern and southern hemisphere. The
pseudo-temperature map shows significant variations across the borders of the
eROSITA bubbles, therefore suggesting temperature variations, possibly linked
to shocks, between the interior of the Galactic outflow and the unperturbed
CGM. In particular, a "shell" of colder material appears to be present close to
the edge of the eROSITA bubbles.
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