A Supernova Factory in Mrk 273?

Abstract

We report on 1.6 and 5.0 GHz observations of the ultraluminous infrared galaxy (ULIRG) Mrk 273, using the European VLBI Network (EVN) and the Multi-Element Radio-Linked Interferometer Network (MERLIN). We also make use of published 1.4 GHz VLBA observations of Mrk 273 by Carilli & Taylor (2000). Our 5 GHz images have a maximum resolution of 5-10 mas, which corresponds to linear resolutions of 3.5-7 pc at the distance of Mrk 273, and are the most sensitive high-resolution radio observations yet made of this ULIRG. Component N1, often pinpointed as a possible AGN, displays a steep spectral index ($\alpha =1.2\pm 0.1;S_{\nu }\propto {\nu }^{-\alpha }$); hence it is very difficult to reconcile with N1 being an AGN, and rather suggests that the compact nonthermal radio emission is produced by an extremely high luminous individual radio supernova (RSN), or a combination of unresolved emission from nested supernova remnants (SNR), luminous RSNe, or both. Component N2 is partly resolved out into several compact radio sources --none of which clearly dominates-- and a region of extended emission about 30 pc in size. The integrated spectral index of this region is flat ($\alpha =0.15\pm 0.1$), which can be interpreted as due to a superposition of several unresolved components, e.g., RSNe or SNRs, whose radio emission peaks at different frequencies and is partially free-free absorbed. The overall extended radio emission from component N is typical of nonthermal, optically thin radio emission ($\alpha =0.8\pm 0.1$), and its 1.4 GHz luminosity ($L_{1.4\mathrm{GHz}}=(2.2\pm 0.1)\times 10^{23}$ WHz${}^{-1}$) is consistent with being produced by relativistic electrons diffused away from supernova remnants in an outburst.

Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal. 6 pages, 3 figures

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• A NICMOS search for obscured Supernovae in starburst galaxies
• The location of an active nucleus and the soft X-ray shadowing by a tidal tail in the ULIRG Mrk 273
• Elliptical Galaxy in the Making: The Dual Active Galactic Nuclei and Metal-enriched Halo of Mrk 273
• Testing a double AGN hypothesis for Mrk 273
• Molecular gas in the northern nucleus of Mrk273: Physical and chemical properties of the disk and its outflow
• Extended Warm Gas in the ULIRG Mrk273: Galactic Outflows and Tidal Debris
• A Multi-wavelength Study of the Dual Nuclei in Mrk 212
• Does a radio jet drive the massive multi-phase outflow in the ultra-luminous infrared galaxy IRAS 10565+2448?
• Seeing the forest and the trees: a radio investigation of the ULIRG Mrk 273
• Radio Variability and Broad-Band Spectra of Infrared Galaxies with and without OH Megamaser Emission
• VLBI Detection of an Active Radio Source Potentially Driving 100-kpc Scale Emission in the Ultraluminous Infrared Galaxy IRAS F01004$-$2237