Optical Spectroscopy of the environment of a ULX in NGC 7331

Abstract

Optical photometric and spectroscopic data are presented that show an association of an ultraluminous X-ray source in NGC 7331 with a young star cluster of mass 1.1e5 solar masses and age 4.25 Myr. If the ULX is part of the bright stellar cluster, then the mass of the progenitor of the compact accretor must have been greater than about 40-50 solar masses in order to already have evolved through the supernova stage to a compact object. The companion star is also likely an evolved massive star. The emission line spectrum of the nebula surrounding the cluster can be interpreted as a result of photoionization by the cluster OB stars with an additional source of shock excitation producing strong [SII], [OI] and NII lines. This additional source appears to be as much as five times more powerful than the supernovae and stellar winds in the cluster can provide. Additional mechanical energy input associated with the ULX itself can help explain the residual shock excited line luminosities of the emission region.

17 pages, accepted to ApJ

References in corpus (4)

• Spectroscopy of Optical Counterparts of Ultraluminous X-ray Sources
• A ULX microquasar in NGC 5408?
• Ultraluminous X-ray Sources: Bubbles and Optical Counterparts
• The Ultraluminous X-ray Source in Holmberg IX and its Environment

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• Ultraluminous X-ray Sources in Seven Edge-On Spiral Galaxies
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