Metal-THINGS: On the Metallicity and Ionization of ULX Sources in NGC 925

• Published in: The Astrophysical journal Vol. 906; no. 1; pp. 42 - 52
• Main Authors: Lara-López, Maritza A., Zinchenko, Igor A., Pilyugin, Leonid S., Gunawardhana, Madusha L. P., López-Cruz, Omar, O’Sullivan, Shane P., Feltre, Anna, Rosado, Margarita, Sánchez-Cruces, Mónica, Chevallard, Jacopo, De Rossi, Maria Emilia, Dib, Sami, Fritz, Jacopo, Fuentes-Carrera, Isaura, Garduño, Luis E., Ibar, Eduardo
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.01.2021; IOP Publishing; American Astronomical Society
• Subjects: Abundance ratios; Accretion; Astrophysics; Binary stars; Chemical abundances; Context; Deposition; Emission line galaxies; Ionization; Kinematics; Metallicity; Nebulae; Neutron stars; Optical properties; Parameters; Sciences of the Universe; Spectroscopy; Spiral galaxies; Star formation; Stellar evolution; X ray binaries; X ray stars; X-ray sources; Chemical abundances; Abundance ratios; Spectroscopy; Emission line galaxies; Ionization; X-ray sources
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/abc892

Abstract We present an analysis of the optical properties of three Ultra Luminous X-ray (ULX) sources identified in NGC 925. We use Integral field unit data from the George Mitchel spectrograph in the context of the Metal-THINGS survey. The optical properties for ULX-1 and ULX-3 are presented, while the spaxel associated with ULX-2 had a low S/N, which prevented its analysis. We also report the kinematics and dimensions of the optical nebula associated with each ULX using ancillary data from the PUMA Fabry–Perot spectrograph. A BPT analysis demonstrates that most spaxels in NGC 925 are dominated by star-forming regions, including those associated with ULX-1 and ULX-3. Using the resolved gas-phase metallicities, a negative metallicity gradient is found, consistent with previous results for spiral galaxies, while the ionization parameter tends to increase radially throughout the galaxy. Interestingly, ULX-1 shows a very low gas metallicity for its galactocentric distance, identified by two independent methods, while exhibiting a typical ionization. We find that such low gas metallicity is best explained in the context of the high-mass X-ray binary population, where the low-metallicity environment favors active Roche lobe overflows that can drive much higher accretion rates. An alternative scenario invoking accretion of a low-mass galaxy is not supported by the data in this region. Finally, ULX-3 shows both a high metallicity and ionization parameter, which is consistent with the progenitor being a highly accreting neutron star within an evolved stellar population region.