A very small interstellar neutral hydrogen cloud observed with VLBI techniques.
Abstract
The letter reports VLBI observations of neutral hydrogen absorption in front of quasar 3C 147. The results show a variation in the optical depth of interstellar H I with a scale no larger than 0.16 arcsec. Assuming that a cloud of higher density superposed on a slowly varying background is being observed, a column density of 10 to the 20th power atoms/sq cm is estimated for the H I cloud along with a maximum probable distance of 600 pc, a linear diameter of 70 AU, a density of 100,000 atoms/cu cm, and a mass of 3 ten-millionths of a solar mass. It is noted that this cloud is smaller by several orders of magnitude than any H I cloud previously observed and that its size and density are more similar to those associated with dense molecular clouds.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1976
- DOI:
- 10.1086/182145
- Bibcode:
- 1976ApJ...206L.113D
- Keywords:
-
- Gas Density;
- Hydrogen Clouds;
- Interstellar Gas;
- Quasars;
- Radio Interferometers;
- Density Distribution;
- Inhomogeneity;
- Size (Dimensions);
- Astronomy