Metal-THINGS: On the metallicity and ionization of ULX sources in NGC
  925
  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 favours 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.
