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2013ApJ...767L..32Y
ALMA Observations of the Galactic Center: SiO Outflows and High-mass Star Formation near Sgr A*
Yusef-Zadeh, F. ( Department of Physics and Astronomy and Center for Interdisciplinary Research in Astronomy, Northwestern University, Evanston, IL 60208, USA ); Royster, M. ( Department of Physics and Astronomy and Center for Interdisciplinary Research in Astronomy, Northwestern University, Evanston, IL 60208, USA ); Wardle, M. ( Department of Physics and Astronomy, and Centre for Astronomy, Astrophysics, & Astrophotonics, Macquarie University, Sydney, NSW 2109, Australia ); Arendt, R. ( CREST/UMBC/NASA GSFC, Code 665, Greenbelt, MD 20771, USA ); Bushouse, H. ( Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA ); Lis, D. C. ( California Institute of Technology, MC 320-47, Pasadena, CA 91125, USA ); Pound, M. W. ( Department of Astronomy, University of Maryland, MD 20742, USA ); Roberts, D. A. ( Department of Physics and Astronomy and Center for Interdisciplinary Research in Astronomy, Northwestern University, Evanston, IL 60208, USA ); Whitney, B. ( Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA ); Wootten, A. ( National Radio Astronomy Observatory, Charlottesville, VA 22903, USA ) show affiliations
The Astrophysical Journal Letters, Volume 767, Issue 2, article id. L32, 7 pp. (2013).
Published in Apr 2013
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) ~1014 cm-2, and the H2 gas density n_H_2=(3{--}9)\times 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 104-105 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.
Keywords:
Free Keywords: Astrophysics - Galaxy Astrophysics; Galaxy: center; ISM: jets and outflows; ISM: molecules; stars: protostars
Astronomy: Galaxy: center; ISM: jets and outflows; ISM: molecules; stars: protostars
arXiv: Astrophysics - Galaxy Astrophysics
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