The Discovery of a Molecular Cavity in the Norma Near Arm Associated with H.E.S.S γ-ray Source Located in the Direction of Westerlund 1
Abstract
We report on the discovery of a molecular cavity in the Norma near arm in the general direction of Westerlund 1 (Wd1), but not associated with it. The cavity has a mean radial velocity of -91.5 km s-1, which differs by as much as ~40 km s-1 from the mean radial velocity of the Wd1 stars. The cavity is surrounded by a fragmented molecular shell of an outer diameter of about 100 pc and 106 M sun, which is expanding at velocities of 6 to 8 km s-1. The amount of kinetic energy involved in the expanding shell is ~1051 erg. Inside this cavity, the atomic H I gas surface density is also the lowest. Structure of the extended Very High Energetic γ-ray emission, recently reported by the H.E.S.S. collaboration, coincides with the cavity. The observed morphology suggests that the inner wall of the molecular shell is the zone of the γ-ray emission, and not the dense gas surrounding massive stars of Wd1 as had been speculated by the H.E.S.S. collaboration. A likely candidate responsible for creating the observed cavity and the γ-ray emission is the pulsar PSR J1648 - 4611.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 2010
- DOI:
- 10.1088/2041-8205/713/1/L45
- arXiv:
- arXiv:1003.1734
- Bibcode:
- 2010ApJ...713L..45L
- Keywords:
-
- gamma rays: general;
- ISM: clouds;
- ISM: molecules;
- ISM: structure;
- open clusters and associations: individual: Westerlund 1;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in The Astrophysical Journal Letters