The metallicity of the nebula surrounding the ultra-luminous X-ray source NGC 1313 X-2

Abstract

Recent models of the formation of ultra-luminous X-ray sources (ULXs) predict that they preferentially form in low-metallicity environments. We look at the metallicity of the nebula surrounding NGC 1313 X-2, one of the best-studied ULXs. Simple estimates, based on the extrapolation of the metallicity gradient within NGC 1313, or on empirical calibrations (relating metallicity to strong oxygen lines) suggest a quite low metal content (Z ~ 0.1 Zsun). But such estimates do not account for the remarkably strong X-ray flux irradiating the nebula. Then, we build photoionization models of the nebula using CLOUDY; using such models, the constraints on the metallicity weaken substantially, as we find 0.15 Zsun <= Z <= 0.5 Zsun.

4 pages. Accepted for publication in the Astronomische Nachrichten, to appear in the proceedings of the conference "Ultra-Luminous X-ray sources and Middle Weight Black Holes" (Madrid, May 24-26, 2010)

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Cited by in corpus (4)

• X-ray spectral states and metallicity in the ultraluminous X-ray sources NGC 1313 X-1 and X-2
• Roche-lobe overflow systems powered by black holes in young star clusters: the importance of dynamical exchanges
• The Local Environment of Ultraluminous X-ray Sources Viewed by XMM Newton's Optical Monitor
• VLT MUSE observations of the bubble nebula around NGC 1313 X-2 and evidence for additional photoionization