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Peer-reviewedCC BY 4.0The Astrophysical Journal

Probing the All-sky Distribution of Soft X-Ray Emission Associated with the Milky Way

  • Kazuki Ampuku1
  • Ikuyuki Mitsuishi1
  • Philip Kaaret2
  • Kyoko Matsushita3
  • Kotaro Fukushima3
  • Lorella Angelini4
  • Dimitra Koutroumpa5
  • K. D. Kuntz4,6
6 affiliations
  1. 1Nagoya University
  2. 2NASA/Marshall Space Flight Center
  3. 3Tokyo University of Science
  4. 4NASA/Goddard Space Flight Center
  5. 5UVSQ Université Paris-Saclay
  6. 6Johns Hopkins University
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Abstract

We present an all-sky analysis of soft X-ray emission associated with the Milky Way using HaloSat and ROSAT data, extending our previous study of five Galactic-plane regions to 330 fields across the sky. We performed uniform spectral fitting with a model including an unabsorbed Local Hot Bubble and two additional absorbed thermal components, representing emission from warm–hot and hot plasma, while accounting for solar wind charge exchange and the cosmic X-ray background. The warm–hot component is often interpreted as emission from the circumgalactic medium, whereas the origin of the hot component remains uncertain. Individual-field fits generally favored the inclusion of the hot component and the field-to-field temperature distributions had medians of kT = 0.19 and 0.74 keV, with 16th–84th percentile ranges of 0.17–0.21 and 0.61–0.90 keV, respectively. The corresponding 16th–84th percentile EM ranges were (1.0–8.2) × 10−2 and (0.5–4.1) × 10−3 cm−6 pc. Stacked spectra from fields within 60∘ ≤ l ≤ 180∘ supported the individual-field results. After excluding bright X-ray sources and large-scale Galactic structures, we modeled the EM distributions of 178 fields using a hybrid spatial framework comprising stellar emission and disk-like and halo-like diffuse-plasma components. The warm–hot emission was described mainly by the disk-like term, whereas the hot emission was described mainly by stellar emission with an additional halo-like term. These results support a widespread two-temperature description and suggest a composite origin for the hot emission.

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Cite

BibTeXRIS
BibTeX
@article{ampuku2026probing,
  title = {{Probing the All-sky Distribution of Soft X-Ray Emission Associated with the Milky Way}},
  author = {Kazuki Ampuku and Ikuyuki Mitsuishi and Philip Kaaret and Kyoko Matsushita and Kotaro Fukushima and Lorella Angelini and Dimitra Koutroumpa and K. D. Kuntz},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aea6ce},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea6ce},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Probing the All-sky Distribution of Soft X-Ray Emission Associated with the Milky Way
AU  - Kazuki Ampuku
AU  - Ikuyuki Mitsuishi
AU  - Philip Kaaret
AU  - Kyoko Matsushita
AU  - Kotaro Fukushima
AU  - Lorella Angelini
AU  - Dimitra Koutroumpa
AU  - K. D. Kuntz
PY  - 2026
DA  - 2026/10/27
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea6ce
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea6ce
AB  - We present an all-sky analysis of soft X-ray emission associated with the Milky Way using HaloSat and ROSAT data, extending our previous study of five Galactic-plane regions to 330 fields across the sky. We performed uniform spectral fitting with a model including an unabsorbed Local Hot Bubble and two additional absorbed thermal components, representing emission from warm–hot and hot plasma, while accounting for solar wind charge exchange and the cosmic X-ray background. The warm–hot component is often interpreted as emission from the circumgalactic medium, whereas the origin of the hot component remains uncertain. Individual-field fits generally favored the inclusion of the hot component and the field-to-field temperature distributions had medians of kT = 0.19 and 0.74 keV, with 16th–84th percentile ranges of 0.17–0.21 and 0.61–0.90 keV, respectively. The corresponding 16th–84th percentile EM ranges were (1.0–8.2) × 10−2 and (0.5–4.1) × 10−3 cm−6 pc. Stacked spectra from fields within 60∘ ≤ l ≤ 180∘ supported the individual-field results. After excluding bright X-ray sources and large-scale Galactic structures, we modeled the EM distributions of 178 fields using a hybrid spatial framework comprising stellar emission and disk-like and halo-like diffuse-plasma components. The warm–hot emission was described mainly by the disk-like term, whereas the hot emission was described mainly by stellar emission with an additional halo-like term. These results support a widespread two-temperature description and suggest a composite origin for the hot emission.
SN  - 1538-4357
SN  - 0004-637X
ER  -