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ALMA Observations of the Galactic Center: SiO Outflows and High-mass Star Formation near Sgr A*

Yusef-Zadeh, F. and Royster, M. and Wardle, M. and Arendt, R. and Bushouse, H. and Lis, D. C. and Pound, M. W. and Roberts, D. A. and Whitney, B. and Wootten, A. (2013) ALMA Observations of the Galactic Center: SiO Outflows and High-mass Star Formation near Sgr A*. Astrophysical Journal Letters, 767 (2). Art. No. L32. ISSN 2041-8205. doi:10.1088/2041-8205/767/2/L32.

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ALMA observations of the Galactic center with a spatial resolution of 2."61 × 0."97 resulted in the detection of 11 SiO (5-4) clumps of molecular gas within 0.6 pc (15") of Sgr A^*, interior to the 2 pc circumnuclear molecular ring. The three SiO (5-4) clumps closest to Sgr A^* show the largest central velocities, ~150 km s^(–1), and the broadest asymmetric line widths with full width zero intensity (FWZI) ~110-147 km s^(–1). The remaining clumps, distributed mainly to the NE of the ionized mini-spiral, have narrow FWZI (~18-56 km s^(–1)). Using CARMA SiO (2-1) data, Large Velocity Gradient modeling of the SiO line ratios for the broad velocity clumps constrains the column density N(SiO) ~10^(14) cm^(–2), and the H_2 gas density n_H_2 = (3-9) x 10^5 cm^(–3) for an assumed kinetic temperature 100-200 K. The SiO clumps are interpreted as highly embedded protostellar outflows, signifying an early stage of massive star formation near Sgr A^* in the last 10^4-10^5 yr. Support for this interpretation is provided by the SiO (5-4) line luminosities and velocity widths which lie in the range measured for protostellar outflows in star-forming regions in the Galaxy. Furthermore, spectral energy distribution modeling of stellar sources shows two young stellar object candidates near SiO clumps, supporting in situ star formation near Sgr A^*. We discuss the nature of star formation where the gravitational potential of the black hole dominates. In particular, we suggest that external radiative pressure exerted on self-shielded molecular clouds enhances the gas density, before the gas cloud becomes gravitationally unstable near Sgr A^*. Alternatively, collisions between clumps in the ring may trigger gravitational collapse.

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Arendt, R.0000-0001-8403-8548
Lis, D. C.0000-0002-0500-4700
Additional Information:© 2013 American Astronomical Society. Received 2013 February 12; accepted 2013 March 12; published 2013 April 5. We thank Stefan Gillessen for providing us with VLT images. This work is partially supported by grants AST-0807400 from the NSF. This paper makes use of the following ALMA data: ADS/JAO.ALMA\#2011.0.0005.SVProject code. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with the NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ.
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Subject Keywords:Galaxy: center; ISM: jets and outflows; ISM: molecules; stars: protostars
Issue or Number:2
Record Number:CaltechAUTHORS:20130517-150520402
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Official Citation:ALMA Observations of the Galactic Center: SiO Outflows and High-mass Star Formation near Sgr A* F. Yusef-Zadeh, M. Royster, M. Wardle, R. Arendt, H. Bushouse, D. C. Lis, M. W. Pound, D. A. Roberts, B. Whitney, and A. Wootten doi:10.1088/2041-8205/767/2/L32
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38572
Deposited By: Ruth Sustaita
Deposited On:20 May 2013 16:19
Last Modified:09 Nov 2021 23:38

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