Tuesday, May 7th 2013

Just one paper today, but looks interesting – FIR lines in the center of the Milky Way with PACS and SPIRE.

Title: Far-Infrared Spectroscopy of the Galactic Center. Hot Molecular Gas: Shocks versus Radiation near SgrA*
Authors: Goicoechea, Javier R.; Etxaluze, M.; Cernicharo, J.; Gerin, M.; Neufeld, D. A.; Contursi, A.; Bell, T. A.; De Luca, M.; Encrenaz, P.; Indriolo, N.; Lis, D. C.; Polehampton, E. T.; Sonnentrucker, P.
Publication: eprint arXiv:1305.1119
Publication Date: 05/2013
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics
Comment: 20 pages, 3 figures, 1 table. Accepted for publication in Astrophysical Journal Letters
Bibliographic Code: 2013arXiv1305.1119G


We present a 52-671um spectral scan toward SgrA* taken with the PACS and SPIRE spectrometers onboard Herschel. The achieved angular resolution allows us to separate, for the first time at far-IR wavelengths, the emission toward the central cavity (gas in the inner central parsec of the galaxy) from that of the surrounding circum-nuclear disk. The spectrum toward SgrA* is dominated by strong [OIII], [OI], [CII], [NIII], [NII], and [CI] fine structure lines (in decreasing order of luminosity) arising in gas irradiated by UV-photons from the central stellar cluster. In addition, rotationally excited lines of 12CO (from J=4-3 to 24-23), 13CO, H2O, OH, H3O+, HCO+ and HCN, as well as ground-state absorption lines of OH+, H2O+, H3O+, CH+, H2O, OH, HF, CH and NH are detected. The excitation of the 12CO ladder is consistent with a hot isothermal component at Tk ~ 10^{3.1} K and n(H2)< 10^4 cm^{-3}. It is also consistent with a distribution of temperature components at higher density with most CO at Tk<300 K. The detected molecular features suggest that, at present, neither very enhanced X-ray, nor cosmic-ray fluxes play a dominant role in the heating of the hot molecular gas. The hot CO component (either the bulk of the CO column or just a small fraction depending on the above scenario) results from a combination of UV- and shock-driven heating. If irradiated dense clumps/clouds do not exist, shocks likely dominate the heating of the hot molecular gas. This is consistent with the high-velocity gas detected toward SgrA*.

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