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

Abstract

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 which exhibits different morphology in the H$\alpha$ and [O III] images. The [O III]/H$\alpha$ ratio map shows that the H$\alpha$-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 to the bubble as $P_w\sim 5\times 10^{40}$ erg s${}^{-1}$ and the corresponding bubble age of $\sim 7\times 10^5$ yr. Relativistic jets are needed to provide such level of mechanical power with a mass-loss rate of $\sim 10^{-7}{M}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$. Besides the accretion, the black hole spin is likely an additional energy source for the super-Eddington jet power.

17 pages, 10 figures, accepted by ApJ

References in corpus (25)

• Array Programming with NumPy
• The MAPPINGS III Library of Fast Radiative Shock Models
• An Ultraluminous X-ray Source Powered by An Accreting Neutron Star
• An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907
• The power of relativistic jets is larger than the luminosity of their accretion disks
• Discovery of a 0.42-s pulsar in the ultraluminous X-ray source NGC 7793 P13
• Discovery of coherent pulsations from the Ultraluminous X-ray Source NGC 7793 P13
• The Nature of SS433 and the Ultraluminous X-ray Sources
• A mass of less than 15 solar masses for the black hole in an ultraluminous X-ray source
• The Panchromatic Hubble Andromeda Treasury X. Ultraviolet to Infrared Photometry of 117 Million Equidistant Stars
• MegaPipe: the MegaCam image stacking pipeline at the Canadian Astronomical Data Centre
• The Abundance Properties of Nearby Late-Type Galaxies.I. The Data
• The discovery of weak coherent pulsations in the ultraluminous X-ray source NGC 1313 X-2
• XMM-Newton campaign on the ultraluminous X-ray source NGC 247 ULX-1: outflows
• Optical Properties of the Ultraluminous X-ray Source Holmberg IX X-1 and its Stellar Environment
• New Hubble Space Telescope imaging of the counterparts to six ultraluminous X-ray sources
• Ionised Emission and Absorption in a Large Sample of Ultraluminous X-ray Sources
• A new candidate pulsating ULX in NGC 7793
• Asymmetric MHD Outflows/Jets from Accreting T Tauri Stars
• MUSE spectroscopy of the ULX NGC 1313 X-1: a shock-ionised bubble, an X-ray photoionised nebula, and two supernova remnants
• Exploring the Dust Content of Galactic Winds with Herschel. I. NGC 4631
• The ultraluminous X-ray source bubble in NGC 5585
• Linking soft excess in ultraluminous X-ray sources with optically thick wind driven by supercritical accretion
• Investigating the nature of the ultraluminous X-ray sources in the galaxy NGC 925
• VLT MUSE observations of the bubble nebula around NGC 1313 X-2 and evidence for additional photoionization

Cited by in corpus (2)

• New Transient ULX Candidate in NGC 4254: Evidence of Circumbinary Disk?
• Identification of three new ultraluminous X-ray sources in NGC 4631 and NGC 1097: Evidence for stellar-mass black holes