2023ApJ...946...72G -
Astrophys. J., 946, 72 (2023/April-1)
Bubble in the Whale: Identifying the Optical Counterparts and Extended Nebula for the Ultraluminous X-Ray Sources in NGC 4631.
GUO J., WU J., FENG H., CAI Z., ZHOU P., ZHOU C., ZHANG S., WANG J., SUN M., GU W.-M., WENG S.-S. and LIU J.
Abstract (from CDS):
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 Hα and [O III] images. The [O III]/Hα ratio map shows that the Hα-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 Pw ∼ 5 × 1040 erg s–1 and the corresponding bubble age as ∼7 × 105 yr. Relativistic jets are needed to provide such a level of mechanical power with a mass-loss rate of ∼10–7M⊙ yr–1. Besides the accretion, the black hole spin is likely an additional energy source for the super-Eddington jet power.
Abstract Copyright:
© 2023. The Author(s). Published by the American Astronomical Society.
Journal keyword(s):
Ultraluminous x-ray sources - Emission nebulae - Accretion - X-ray binary stars
Simbad objects:
15
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