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The Radio Spectra of the Compact Sources in Arp 220: A Mixed Population of Supernovae and Supernova Remnants

Parra, Rodrigo and Conway, John E. and Diamond, Philip J. and Thrall, Hannah and Lonsdale, Colin J. and Lonsdale, Carol J. and Smith, Harding E. (2007) The Radio Spectra of the Compact Sources in Arp 220: A Mixed Population of Supernovae and Supernova Remnants. Astrophysical Journal, 659 (1). pp. 314-330. ISSN 0004-637X.

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We report the first detection at multiple radio wavelengths (13, 6, and 3.6 cm) of the compact sources within both nuclei of the ultraluminous infrared galaxy Arp 220, presenting radio spectra of the 18 detected sources. In just over half of these, we find that these spectra and other properties are consistent with the standard model of powerful Type IIn supernovae interacting with their preexplosion stellar wind. The rate of appearance of new radio sources identified with these supernova events suggests that an unusually large fraction of core-collapse supernovae in Arp 220 are highly luminous, possibly implying a radically different stellar initial mass function or stellar evolution compared to galactic disks. Another possible explanation invokes very short (~3 × 10^5 yr) intense (~10^3 M_⊙ yr^(-1)) star formation episodes with a duty cycle of ~10%. A second group of our detected sources, consisting of the brightest and longest monitored sources at 18 cm, do not easily fit the radio supernova model. These sources show a range of spectral indexes from -0.2 to -1.9. We propose that these are young supernova remnants that have just begun interacting with a surrounding ISM with a density between 10^4 and 10^5 cm^(-3). One source is probably resolved at 3.6 cm wavelength with a diameter 0.9 pc. In the western nucleus we estimate that the ionized component of the ISM gives rise to foreground free-free absorption with opacity at 18 cm of <0.6 along the majority of lines of sight. Other sources may be affected by absorption with opacity in the range 1-2. These values are consistent with previous models as fitted to the radio recombination lines and the continuum spectrum.

Item Type:Article
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URLURL TypeDescription
Lonsdale, Colin J.0000-0003-0898-406X
Lonsdale, Carol J.0000-0003-0898-406X
Additional Information:© 2007 The American Astronomical Society. Received 2006 September 22; accepted 2006 December 2. R. P. acknowledges a Chalmers University Ph.D. student stipend, and J. C. acknowledges a Swedish VR grant. This work was partially supported by NSF grant AST 03-52953 to Haystack Observatory. The European VLBI Network is a joint facility of European, Chinese, South African, and other radio astronomy institutes funded by their national research councils. The Arecibo Observatory is the principal facility of the National Astronomy and Ionosphere Center, which is operated by the Cornell University under a cooperative agreement with the National Science Foundation. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We thank the anonymous referee for his/her valuable comments and suggestions.
Funding AgencyGrant Number
Chalmers University Ph.D. student stipendUNSPECIFIED
NSFAST 03-52953
Subject Keywords:galaxies : individual (Arp 220); galaxies : starburst
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Record Number:CaltechAUTHORS:20100318-094036788
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17769
Deposited By: Tony Diaz
Deposited On:20 Mar 2010 03:56
Last Modified:09 Mar 2020 13:19

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