Volume 595, November 2016
|Number of page(s)||27|
|Section||Interstellar and circumstellar matter|
|Published online||25 October 2016|
1 European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
2 National Radio Astronomy Observatory, Socorro, NM 87801, USA
3 Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
4 ALLEGRO/Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
5 Instituto de Radioastronomía y Astrofísica, UNAM, A.P. 3-72, Xangari, 58089 Morelia, Mexico
6 University Observatory/Excellence Cluster “Universe” Scheinerstraße 1, 81679 München, Germany
7 CASA, University of Colorado, 389-UCB, Boulder, CO 80309, USA
8 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
9 LASP, University of Colorado, 600 UCB, Boulder, CO 80309, USA
10 SOFIA Science Center, NASA Ames Research Center, M/S 232-12, Moffett Field, CA 94035, USA
11 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
12 Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Straße 1, 85748 Garching, Germany
13 Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, 69120 Heidelberg, Germany
Received: 15 February 2016
Accepted: 22 June 2016
We present new JVLA observations of the high-mass cluster-forming region W51A from 2 to 16 GHz with resolution θfwhm ≈ 0.3−0.5″. The data reveal a wealth of observational results: (1) Currently forming, very massive (proto-O) stars are traced by o - H2CO21,1−21,2 emission, suggesting that this line can be used efficiently as a massive protostar tracer; (2) there is a spatially distributed population of ≲mJy continuum sources, including hypercompact H ii regions and candidate colliding wind binaries, in and around the W51 proto-clusters; and (3) there are two clearly detected protoclusters, W51e and W51 IRS2, that are gas-rich but may have most of their mass in stars within their inner ≲0.05 pc. The majority of the bolometric luminosity in W51 most likely comes from a third population of OB stars between these clusters. The presence of a substantial population of exposed O-stars coincident with a population of still-forming massive stars, together with a direct measurement of the low mass loss rate via ionized gas outflow from W51 IRS2, implies that feedback is ineffective at halting star formation in massive protoclusters. Instead, feedback may shut off the large-scale accretion of diffuse gas onto the W51 protoclusters, implying that they are evolving toward a state of gas exhaustion rather than gas expulsion. Recent theoretical models predict gas exhaustion to be a necessary step in the formation of gravitationally bound stellar clusters, and our results provide an observational validation of this process.
Key words: Hiiregions / circumstellar matter / radio continuum: ISM / radio lines: ISM / stars: massive / stars: protostars
This paper and all related analysis code are available on the web at https://github.com/adamginsburg/paper_w51_evla
Table A.1 and final data (FITS files) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/595/A27
© ESO, 2016
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