The Thinnest Cold H I Clouds in the Diffuse Interstellar Medium?
Abstract
We confirm and discuss recently discovered cold H I clouds with column densities among the lowest ever detected. The column densities of the cold neutral medium (CNM) toward 3C 286 and 3C 287 are ~1018 cm-2, below an observational lower limit and also below tiny-scale atomic clouds detected by VLBI and time-variable profiles against pulsars. These column densities are close to the minimum imposed by thermal evaporation. The ratios of the CNM to total H I toward 3C 286 and 3C 287 are ~4% and <~2%, respectively. We discuss the CNM fraction and the CNM clouds in relation to several theoretical models.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2005
- DOI:
- 10.1086/432533
- arXiv:
- arXiv:astro-ph/0505106
- Bibcode:
- 2005ApJ...631..371S
- Keywords:
-
- ISM: Clouds;
- ISM: Structure;
- Radio Lines: ISM;
- Astrophysics
- E-Print:
- small changes, accepted by ApJ