Query : 2004A&A...426..201D

2004A&A...426..201D - Astronomy and Astrophysics, volume 426, 201-212 (2004/10-4)

The molecular clouds in the environs of the supernova remnants G349.7+0.2 and G18.8+0.3.


Abstract (from CDS):

We present the results of a new high-resolution study of the molecular gas associated with the supernova remnants (SNRs) G349.7+0.2 and G18.8+0.3. The observations were performed with the SEST telescope in the 12CO J=1-0, 2-1 and 3-2 lines (beams of 45'', 23'' and 15'', respectively). The present observations have provided, for the two SNRs, new evidence in support of the existence of physical interaction between the SN shocks and the adjoining molecular clouds. In the case of G349.7+0.2, the new observations revealed for the first time the internal structure of the shocked cloud, as well as the kinematical consequences of the impact of the SNR shock on the molecular cloud. From these observations we were able to constrain the conditions of the pre-shocked gas. The molecular cloud associated with G349.7+0.2, centered near vLSR=+16.2km/s, has a linear size of about 7pc, a mass of ∼104M and a volume density of ∼103cm–3. The high line ratios derived are indicative of the existence of shocks in the cloud. From the asymmetries observed in the line shapes we propose that the SN shock cloud is running into the denser part of the cloud and has probably begun to disrupt it, pushing the eastern component clumps away from us, and the western fragments toward us. After comparing our estimates of the column density of the intervening gas with similar calculations based on ASCA X-rays spectral fitting we conclude that the best way to make these results compatible is by assuming that the associated cloud is placed behind G349.7+0.2 along the line of sight, and the SNR/molecular cloud encounter is taking place on the far side of the SNR. This model also provides a natural explanation for the lack of strong X-ray absorption in the central region of G349.7+0.2. Evaporation of part of the associated cloud must be responsible for the central X-ray emission. The comparison with IRAS infrared data provides additional support for the hypothesis of SNR/cloud physical interaction. From the study of the molecular gas in the neighborhood of the five OH (1720MHz) masers detected in G349.7+0.2 we find that in three cases the maser peak velocity coincides with the local CO peak velocity, while in the remaining two cases the maser peak velocity agrees with a secondary, blended CO component. We conclude that the masers are excited at the sites where a non-dissociative C-type shock, locally transverse to the line of sight (or forming a large angle with it), hits a denser molecular clump. For the SNR G18.8+0.3, the new higher resolution observations have revealed excellent morphological agreement between one of the cloud components and the SNR shock front towards the eastern limb. The associated molecular mass is estimated to be ∼4.4x104M and the cloud volume density ∼1200cm–3. The analysis of the line ratios in this case revealed a maximum of R2–1/1–0=1.25 at a position that exactly matches an indentation in the radio continuum emission in the remnant's shell, providing additional evidence of SNR/molecular cloud interaction.

Abstract Copyright:

Journal keyword(s): ISM: molecules - ISM: clouds - ISM: supernova remnants - radio lines: ISM

Nomenclature: Table 3: [DGR2004] Cloud A (Nos A-B).

Simbad objects: 8

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Number of rows : 8
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 IRAS 17146-3723 FIR 17 17 59.9740 -37 26 14.193           ~ 11 0
2 SNR G349.7+00.2 SNR 17 18 10.160 -37 18 53.80           ~ 191 0
3 SNR G006.4-00.1 SNR 18 00 31.2011719 -23 25 48.001099           ~ 748 1
4 [DGR99] Cloud 3 Cld 18 24 -12.5           ~ 2 1
5 SNR G018.8+00.3 SNR 18 24.0 -12 23           ~ 105 0
6 [DGR2004] Cloud B Cld 18 24 10 -12 29.5           ~ 1 1
7 [DGR2004] Cloud A Cld 18 24 13 -12 27.8           ~ 1 1
8 SNR G034.6-00.5 SNR 18 56 10.650 +01 13 21.30           ~ 971 2

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