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 Z_⊙). 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 Z_⊙ ≤Z ≤0.5 Z_⊙.
- Publication:
-
Astronomische Nachrichten
- Pub Date:
- May 2011
- DOI:
- 10.1002/asna.201011512
- arXiv:
- arXiv:1009.5708
- Bibcode:
- 2011AN....332..418R
- Keywords:
-
- galaxies: abundances;
- galaxies: individual (NGC1313);
- H II regions;
- X-rays: individual (NGC 1313 X-2);
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 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)