Publication Date:
2016-08-04
Description:
We present 12 mm Mopra observations of the dense (〉10 3 cm –3 ) molecular gas towards the north-east of the W28 supernova remnant (SNR). This cloud is spatially well matched to the TeV gamma-ray source HESS J1801–233 and is known to be an SNR-molecular cloud interaction region. Shock-disruption is evident from broad NH 3 (1,1) spectral linewidths in regions towards the W28 SNR, while strong detections of spatially extended NH 3 (3,3), NH 3 (4,4) and NH 3 (6,6) inversion emission towards the cloud strengthen the case for the existence of high temperatures within the cloud. Velocity dispersion measurements and NH 3 ( n , n )/(1,1) ratio maps, where n = 2, 3, 4 and 6, indicate that the source of disruption is from the side of the cloud nearest to the W28 SNR, suggesting that it is the source of cloud-disruption. Towards part of the cloud, the ratio of ortho to para-NH 3 is observed to exceed 2, suggesting gas-phase NH 3 enrichment due to NH 3 liberation from dust-grain mantles. The measured NH 3 abundance with respect to H 2 is ~(1.2 ± 0.5) x 10 –9 , which is not high, as might be expected for a hot, dense molecular cloud enriched by sublimated grain-surface molecules. The results are suggestive of NH 3 sublimation and destruction in this molecular cloud, which is likely to be interacting with the W28 SNR shock.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
