A broad linewidth, compact, millimeter-bright molecular emission line source near the Galactic Center
Abstract
A compact source, G0.02467-0.0727, was detected in ALMA \threemm observations in continuum and very broad line emission. The continuum emission has a spectral index $α\approx3.3$, suggesting that the emission is from dust. The line emission is detected in several transitions of CS, SO, and SO$_2$ and exhibits a line width FWHM $\approx160$ \kms. The line profile appears Gaussian. The emission is weakly spatially resolved, coming from an area on the sky $\lesssim1"$ in diameter ($\lesssim10^4$ AU at the distance of the Galactic Center; GC). The centroid velocity is $v_{LSR}\approx40$-$50$ \kms, which is consistent with a location in the Galactic Center. With multiple SO lines detected, and assuming local thermodynamic equilibrium (LTE) conditions, $T_\mathrm{LTE} = 13$ K, which is colder than seen in typical GC clouds, though we cannot rule out low-density, subthermally excited, warmer gas. Despite the high velocity dispersion, no emission is observed from SiO, suggesting that there are no strong ($\gtrsim10~\mathrm{km~s}^{-1}$) shocks in the molecular gas. There are no detections at other wavelengths, including X-ray, infrared, and radio. We consider several explanations for the Millimeter Ultra-Broad Line Object (MUBLO), including protostellar outflow, explosive outflow, collapsing cloud, evolved star, stellar merger, high-velocity compact cloud, intermediate mass black hole, and background galaxy. Most of these conceptual models are either inconsistent with the data or do not fully explain it. The MUBLO is, at present, an observationally unique object.
Authors 39
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Department of Astronomy , University of Florida , P.O. Box 112055 , Gainesville , FL 32611
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University of Colorado Boulder
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Center for Astrophysics and Space Astronomy , Department of Astrophysical and Planetary Sciences University of Colorado , Boulder , CO 80389 , USA
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Affiliation as printed
European Southern Observatory (ESO) , Karl-Schwarzschild-Straße 2 , 85748 Garching , Germany
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Affiliation as printed
Department of Physics , University of Connecticut , 196A Auditorium Road , Unit 3046 , Storrs , CT 06269 , USA
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Affiliation as printed
Department of Astronomy , University of Florida , P.O. Box 112055 , Gainesville , FL 32611
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National Radio Astronomy Observatory
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National Radio Astronomy Observatory , 520 Edgemont Road , Charlottesville , VA 22903 , USA
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Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik , Giessenbachstrasse 1 , D-85748 Garching , Germany
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Affiliation as printed
Centro de Astrobiología (CAB) , CSIC-INTA , Carretera de Ajalvir km 4 , Torrejón de Ardoz , 28850 Madrid , Spain
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Leiden University · Leiden Observatory
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Leiden Observatory , Leiden University , P.O. Box 9513 , 2300 RA Leiden , The Netherlands
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Affiliation as printed
Department of Astronomy , University of Florida , P.O. Box 112055 , Gainesville , FL 32611
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Max Planck Institute for Astronomy · Liverpool John Moores University
Affiliation as printed
Astrophysics Research Institute , Liverpool John Moores University , IC2 , Liverpool Science Park , 146 Brownlow Hill , Liverpool L3 5RF , UK
Max Planck Institute for Astronomy , Königstuhl 17 , D-69117 Heidelberg , Germany
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University of Wisconsin–Madison
Affiliation as printed
Department of Physics , University of Wisconsin-Madison , Madison , WI , 53706 , USA
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National Radio Astronomy Observatory · University of Florida
Affiliation as printed
Department of Astronomy , University of Florida , P.O. Box 112055 , Gainesville , FL 32611
National Radio Astronomy Observatory , 520 Edgemont Road , Charlottesville , VA 22903-2475 , USA
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Massachusetts Institute of Technology
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Haystack Observatory , Massachusetts Institute of Technology , 99 Milsstone Road , Westford , MA 01886 , USA
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Affiliation as printed
Universität Heidelberg , Interdisziplinäres Zentrum für Wissenschaftliches Rechnen , Im Neuenheimer Feld 205 , 69120 Heidelberg , Germany
Universität Heidelberg , Zentrum für Astronomie , Institut für Theoretische Astrophysik , Albert-Ueberle-Str. 2 , 69120 Heidelberg , Germany
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Affiliation as printed
Department of Astronomy , Box 351580 , University of Washington , Seattle , WA 98195 , USA
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Liverpool John Moores University
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Astrophysics Research Institute , Liverpool John Moores University , IC2 , Liverpool Science Park , 146 Brownlow Hill , Liverpool L3 5RF , UK
COOL Research DAO
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Chinese Academy of Sciences · Shanghai Astronomical Observatory
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Shanghai Astronomical Observatory , Chinese Academy of Sciences , 80 Nandan Road , Shanghai 200030 , People's Republic of China
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Affiliation as printed
Department of Physics and Astronomy , University of Kansas , 1251 Wescoe Hall Drive , Lawrence , KS 66045 , USA
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University of California, Los Angeles
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Department of Physics & Astronomy , University of California , Los Angeles , Los Angeles , CA 90095-1547 , USA
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Affiliation as printed
Department of Physics , Faculy of Science and Technology , Keio University , 3-14-1 Hiyoshi , Kohoku-ku , Yokohama , Kanagawa 223-8522 , Japan
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Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik , Giessenbachstrasse 1 , D-85748 Garching , Germany
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Massachusetts Institute of Technology
Affiliation as printed
Haystack Observatory , Massachusetts Institute of Technology , 99 Milsstone Road , Westford , MA 01886 , USA
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Affiliation as printed
Centro de Astrobiología (CAB) , CSIC-INTA , Carretera de Ajalvir km 4 , Torrejón de Ardoz , 28850 Madrid , Spain
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Affiliation as printed
Department of Astronomy , University of Florida , P.O. Box 112055 , Gainesville , FL 32611
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Center for Astrophysics Harvard & Smithsonian
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Center for Astrophysics | Harvard & Smithsonian , 60 Garden Street , Cambridge , MA 02138
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Affiliation as printed
Institue of Astronomy , The University of Tokyo , Mitaka , Tokyo , 181-0015
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University of Insubria · University of Surrey
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Department of Physics , University of Surrey , Guildford GU2 7XH , UK
Università dell'Insubria , via Valleggio 11 , 22100 Como , Italy
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Center for Astrophysics Harvard & Smithsonian
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Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA 32 Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA 33 Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People's Republic of China 34 Department of Astronomy, School of Physics, Peking University, Beijing, 100871, People's Republic of China 35 Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA, 02138, USA
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Center for Astrophysics Harvard & Smithsonian
Affiliation as printed
Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA 32 Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA 33 Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People's Republic of China 34 Department of Astronomy, School of Physics, Peking University, Beijing, 100871, People's Republic of China 35 Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA, 02138, USA
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Leiden University · Leiden Observatory
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Leiden Observatory , Leiden University , P.O. Box 9513 , 2300 RA Leiden , The Netherlands
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