Probing the All-sky Distribution of Soft X-ray Emission Associated with the Milky Way
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) x 10-2 and (0.5-4.1) x 10-3 cm-6 pc. Stacked spectra from fields within 60 deg. <= l <= 180 deg. 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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BibTeX
@misc{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. Kuntz},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.16688},
eprint = {2609.16688},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05794723v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
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. Kuntz
PY - 2026
DA - 2026/09/15
PB - HAL
DO - 10.48550/arxiv.2609.16688
UR - https://hal.science/hal-05794723v1
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) x 10-2 and (0.5-4.1) x 10-3 cm-6 pc. Stacked spectra from fields within 60 deg. <= l <= 180 deg. 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.
ER -