Bubble in the Whale: Identifying the Optical Counterparts and Extended Nebula for the Ultraluminous X-Ray Sources in NGC 4631

We present a deep optical imaging campaign on the starburst galaxy NGC 4631 with CFHT/MegaCam. By supplementing the HST/ACS and Chandra/ACIS archival data, we search for the optical counterpart candidates of the five brightest X-ray sources in this galaxy, four of which are identified as ultralumino...

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Bibliographic Details
Published in:The Astrophysical journal 2023-04, Vol.946 (2), p.72
Main Authors: Guo, Jing, Wu, Jianfeng, Feng, Hua, Cai, Zheng, Zhou, Ping, Zhou, Changxing, Zhang, Shiwu, Wang, Junfeng, Sun, Mouyuan, Gu, Wei-Min, Weng, Shan-Shan, Liu, Jifeng
Format: Article
Language:English
Subjects:
Accretion
Astrophysics
Black holes
Bubbles
Data search
Deposition
Emission nebulae
Energy sources
Galaxies
Interstellar matter
Interstellar medium
Ionization
Nebulae
Optical counterparts (astronomy)
Photoionization
Starburst galaxies
Ultraluminous x-ray sources
X ray sources
X-ray astronomy
X-ray binary stars
X-rays
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Summary:We present a deep optical imaging campaign on the starburst galaxy NGC 4631 with CFHT/MegaCam. By supplementing the HST/ACS and Chandra/ACIS archival data, we search for the optical counterpart candidates of the five brightest X-ray sources in this galaxy, four of which are identified as ultraluminous X-ray sources (ULXs). The stellar environments of the X-ray sources are analyzed using the extinction-corrected color–magnitude diagrams and the isochrone models. We discover a highly asymmetric bubble nebula around X4 that exhibits different morphology in the H α and [O iii ] images. The [O iii ]/H α ratio map shows that the H α -bright bubble may be formed mainly via the shock ionization by the one-sided jet/outflow, while the more compact [O iii ] structure is photoionized by the ULX. We constrain the bubble expansion velocity and interstellar medium density with the MAPPINGS V code and hence estimate the mechanical power injected into the bubble as P w ∼ 5 × 10 40 erg s −1 and the corresponding bubble age as ∼7 × 10 5 yr. Relativistic jets are needed to provide such a level of mechanical power with a mass-loss rate of ∼10 −7 M ⊙ yr −1 . Besides the accretion, the black hole spin is likely an additional energy source for the super-Eddington jet power.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/acaddd