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Thermal SiO observations of a shell attached to the nonthermal filaments in Sgr A
Author(s) -
Handa Toshihiro,
Sakano Masaaki,
Tsuboi Masato
Publication year - 2003
Publication title -
astronomische nachrichten
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.394
H-Index - 63
eISSN - 1521-3994
pISSN - 0004-6337
DOI - 10.1002/asna.200385061
Subject(s) - shell (structure) , physics , excited state , population , line (geometry) , astrophysics , morphology (biology) , thermal , shock wave , atomic physics , materials science , composite material , geometry , thermodynamics , demography , mathematics , sociology , biology , genetics
The CS observations with NRO 45 m telescope reveal that a dense molecular shell is located between Sgr A and the nonthermal filaments of the radio arc, and that the shell shows an interacting feature with the nonthermal filaments (Tsuboi et al. 1997). The shell is associated with X‐ray emission observed with ASCA and Chandra (Yusef‐Zadah et al. 2002). These result suggests the shell is formed by a shock. The SiO lines in the v = 0 state are thermally excited and are thought to be a shock tracer. They are good probes to investigate the physical property of the shell. We observed the shell in SiO ( J = 1 − 0, v = 0) and SiO ( J = 2 − 1, v = 0) using the NRO 45 m telescope. Features associated with the shell clearly appear in both the SiO lines. The morphology of the shell in both SiO lines after adjusting the beamsize effect is similar in l − b − v 3‐dimensional space. The intensity ratio of the two SiO lines ( J = 2 − 1 over J = 1 − 0) is uniform over the shell, suggesting the shell is uniform in density. We estimate the average value of the ratio R 2−1/1−0 ≈ 0.9, which means the molecular gas density is about 10 5 cm −3 using multi‐level population analysis with the LVG approximation. The morphology of the shell in SiO lines is quite similar to in the CS line in l − b − v 3‐dimensional space. The intensity ratio of SiO ( J = 1 − 0) to CS ( J = 1 − 0) is almost uniform over the shell and R SiO/CS ≈ 0.24. The ratio of the SiO ( J = 1− 0) line over the CS ( J = 1− 0) line is about 0.24, which means the relative abundance of SiO over CS, X(SiO)/X(CS) ≈ 0.05 − 0.13 using multi‐level population analysis with the LVG approximation. It is close to the value found in an SNR shell.