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Sio emission as a tracer of x-ray dominated chemistry in the Galactic center

Amo-Baladrón, M. A. and Martín-Pintado, J. and Morris, M. R. and Muno, M. P. and Rodríguez-Fernández, N. J. (2009) Sio emission as a tracer of x-ray dominated chemistry in the Galactic center. Astrophysical Journal, 694 (2). pp. 943-950. ISSN 0004-637X. doi:10.1088/0004-637X/694/2/943.

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We present emission maps of the Sgr A molecular cloud complex at the Galactic center (GC) in the J = 2 → 1 line of SiO observed with the IRAM 30 m telescope at Pico Veleta. Comparing our SiO(2–1) data cube with that of CS(1–0) emission with similar angular and velocity resolution, we find a correlation between the SiO/CS line intensity ratio and the equivalent width of the Fe Kα fluorescence line at 6.4 keV. We discuss the SiO abundance enhancement in terms of the two most plausible scenarios for the origin of the 6.4 keV Fe line: X-ray reflection nebula (XRN) and low-energy cosmic rays (LECRs). Both scenarios could explain the enhancement in the SiO/CS intensity ratio with the intensity of the 6.4 keV Fe line, but both present difficulties. The XRN scenario requires a population of very small grains to produce the SiO abundance enhancement, together with a past episode of bright X-ray emission from some source in the GC, possibly the central supermassive black hole, SgrA∗,~300 yr ago. The LECR scenario needs higher gas column densities to produce the observed 6.4 keV Fe line intensities than those derived from our observations. It is possible to explain the SiO abundance enhancement if the LECRs originate in supernovae and their associated shocks produce the SiO abundance enhancement. However, the LECR scenario cannot account for the time variability of the 6.4 keV Fe line, which can be naturally explained by the XRN scenario.

Item Type:Article
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Morris, M. R.0000-0002-6753-2066
Additional Information:©2009. Received 2008 July 2; accepted 2008 December 30; published 2009 March 20. We thank Professor M. Tsuboi for kindly providing the CS(1–0) data. This work has been supported by the Spanish Ministerio de Educación y Ciencia under projects ESP 2004- 00665 and ESP2007-65812-C02-01 and the “Comunidad de Madrid” Government under PRICIT project S-0505/ESP-0237 (ASTROCAM).
Funding AgencyGrant Number
Ministerio de Educación y Ciencia (MEC)ESP 2004-00665
Ministerio de Educación y Ciencia (MEC)ESP2007-65812-C02-01
Comunidad de MadridPRICIT project S-0505/ESP-0237(ASTROCAM)
Subject Keywords:cosmic rays – Galaxy: center – ISM: clouds – ISM: molecules – radio lines: galaxies – X-rays: ISM
Issue or Number:2
Record Number:CaltechAUTHORS:20090420-142328422
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14031
Deposited By: Marie Noren
Deposited On:21 Apr 2009 17:39
Last Modified:08 Nov 2021 22:42

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