Issue |
A&A
Volume 426, Number 1, October IV 2004
|
|
---|---|---|
Page(s) | 201 - 212 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20041327 | |
Published online | 05 October 2004 |
The molecular clouds in the environs of the supernova remnants G349.7+0.2 and G18.8+0.3
Instituto de Astronomía y Física del Espacio (IAFE), CC 67, Suc. 28, 1428 Buenos Aires, Argentina e-mail: gdubner@iafe.uba.ar
Received:
20
May
2004
Accepted:
25
June
2004
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
km s-1, has a linear size of about 7 pc, a mass
of ~ 104
and a volume density of ~ 103 cm-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 (1720 MHz) 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 ~
and the cloud volume density ~1200 cm-3. The analysis
of the line ratios in this case revealed a maximum of
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.
Key words: ISM: molecules / ISM: clouds / ISM: supernova remnants / radio lines: ISM
© ESO, 2004
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