The CO-H2 conversion factor of diffuse ISM: Bright 12CO emission also traces diffuse gas

Jérôme Pety (1, 2) , Harvey S. Liszt (3) , Robert Lucas (4)

1 IRAM - Institut de RadioAstronomie Millimétrique
2 OP - Observatoire de Paris - Site de Paris
3 NRAO - National Radio Astronomy Observatory
4 JAO - Joint ALMA Office

We show that the XCO factor, which converts the CO luminosity into the column density of molecular hydrogen has similar values for dense, fully molecular gas and for diffuse, partially molecular gas. We discuss the reasons of this coincidence and the consequences for the understanding of the interstellar medium.

Mots clés: ISM: Molecules; ISM: clouds

Domaines: Astrophysique galactique [astro-ph.GA]; Astrophysique galactique [astro-ph.GA]

Jérôme Pety, Harvey S. Liszt, Robert Lucas. The CO-H2 conversion factor of diffuse ISM: Bright 12CO emission also traces diffuse gas. 2011. ⟨hal-00567945⟩