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A 33 GHz Survey of Local Major Mergers: Estimating the Sizes of the Energetically Dominant Regions from High-resolution Measurements of the Radio Continuum

Barcos-Muñoz, L. and Leroy, A. K. and Evans, A. S. and Condon, J. and Privon, G. C. and Thompson, T. A. and Armus, L. and Díaz-Santos, T. and Mazzarella, J. M. and Meier, D. S. and Momjian, E. and Murphy, E. J. and Ott, J. and Sanders, D. B. and Schinnerer, E. and Stierwalt, S. and Surace, J. A. and Walter, F. (2017) A 33 GHz Survey of Local Major Mergers: Estimating the Sizes of the Energetically Dominant Regions from High-resolution Measurements of the Radio Continuum. Astrophysical Journal, 843 (2). Art. No. 117. ISSN 1538-4357.

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We present Very Large Array observations of the 33 GHz radio continuum emission from 22 local ultraluminous and luminous infrared (IR) galaxies (U/LIRGs). These observations have spatial (angular) resolutions of 30–720 pc (0.”07–0.”67) in a part of the spectrum that is likely to be optically thin. This allows us to estimate the size of the energetically dominant regions. We find half-light radii from 30 pc to 1.7 kpc. The 33 GHz flux density correlates well with the IR emission, and we take these sizes as indicative of the size of the region that produces most of the energy. Combining our 33 GHz sizes with unresolved measurements, we estimate the IR luminosity and star formation rate per area and the molecular gas surface and volume densities. These quantities span a wide range (4 dex) and include some of the highest values measured for any galaxy (e.g., Σ^(33 GHz)_(SFR) ⩽ 10^(4.1) M⊙ yr^(-1) kpc^(-2)). At least 13 sources appear Compton thick (N^(33 GHz)_H ⩾ 10^(24) cm(-2)). Consistent with previous work, contrasting these data with observations of normal disk galaxies suggests a nonlinear and likely multivalued relation between star formation rate and molecular gas surface density, though this result depends on the adopted CO-to-H2 conversion factor and the assumption that our 33 GHz sizes apply to the gas. Eleven sources appear to exceed the luminosity surface density predicted for starbursts supported by radiation pressure and supernova feedback; however, we note the need for more detailed observations of the inner disk structure. U/LIRGs with higher surface brightness exhibit stronger [C II] 158 μm deficits, consistent with the suggestion that high energy densities drive this phenomenon.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Barcos-Muñoz, L.0000-0003-0057-8892
Leroy, A. K.0000-0002-2545-1700
Condon, J.0000-0003-4724-1939
Privon, G. C.0000-0003-3474-1125
Díaz-Santos, T.0000-0003-0699-6083
Mazzarella, J. M.0000-0002-8204-8619
Meier, D. S.0000-0001-9436-9471
Momjian, E.0000-0003-3168-5922
Murphy, E. J.0000-0001-7089-7325
Ott, J.0000-0001-8224-1956
Schinnerer, E.0000-0002-3933-7677
Surace, J. A.0000-0001-7291-0087
Walter, F.0000-0003-4793-7880
Additional Information:© 2017 The American Astronomical Society. Received 2016 October 21; revised 2017 May 12; accepted 2017 May 19; published 2017 July 12. We thank the anonymous referee for providing excellent comments that further improved this paper. We thank Jason Chu for making Herschel/PACS images available for quick visual comparison and further discussions on the mid-IR data. Support for this work was provided by the NSF through the Grote Reber Fellowship Program administered by Associated Universities, Inc./National Radio Astronomy Observatory. L.B.-M. was supported by Fulbright, Becas Chile—CONICYT. The work of A.K.L. is supported by the National Science Foundation under grant nos. 1615105 and 1615109. A.S.E., G.C.P., and L.B.-M. were supported by NSF grant AST 1109475. G.C.P. was supported by a FONDECYT Postdoctoral Fellowship (no. 3150361). T.D.-S. acknowledges support from ALMA-CONICYT project 31130005 and FONDECYT regular project 1151239. This research made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration, and NASA's Astrophysics Data System Bibliographic Services. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Errata:Due to an error at the publisher, Figure 1 was published without the second page of panels. The complete version of Figure 1 appears here. IOP Publishing sincerely regrets this error.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Becas Fulbright ChileUNSPECIFIED
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECY)3150361
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)31130005
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECY)1151239
Subject Keywords:galaxies: active – galaxies: interaction – galaxies: starbursts – radio continuum: galaxies
Record Number:CaltechAUTHORS:20170712-100310941
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Official Citation:L. Barcos-Muñoz et al 2017 ApJ 843 117
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79006
Deposited By: Tony Diaz
Deposited On:12 Jul 2017 17:18
Last Modified:02 Nov 2017 20:30

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