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Resolution of the Compact Radio Continuum Sources in Arp220

Fabien Batejat (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; John Conway (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; Rossa Hurley (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; Rodrigo Parra ; Philip Diamond ; Colin Lonsdale ; Carol Lonsdale
The Astrophysical Journal (0004-637X). Vol. 740 (2011), 2,
[Artikel, refereegranskad vetenskaplig]

We present 2 cm and 3.6 cm wavelength very long baseline interferometry images of the compact radio continuum sources in the nearby ultra-luminous infrared galaxy Arp220. Based on their radio spectra and variability properties, we confirm these sources to be a mixture of supernovae (SNe) and supernova remnants (SNRs). Of the 17 detected sources we resolve 7 at both wavelengths. The SNe generally only have upper size limits. In contrast all the SNRs are resolved with diameters ≥0.27 pc. This size limit is consistent with them having just entered their Sedov phase while embedded in an interstellar medium (ISM) of density 104 cm–3. These objects lie on the diameter-luminosity correlation for SNRs (and so also on the diameter-surface brightness relation) and extend these correlations to very small sources. The data are consistent with the relation L ∝ D–9/4. Revised equipartition arguments adjusted to a magnetic field to a relativistic particle energy density ratio of 1% combined with a reasonable synchrotron-emitting volume filling factor of 10% give estimated magnetic field strengths in the SNR shells of ∼15-50 mG. The SNR shell magnetic fields are unlikely to come from compression of ambient ISM fields and must instead be internally generated. We set an upper limit of 7 mG for the ISM magnetic field. The estimated energy in relativistic particles, 2%-20% of the explosion kinetic energy, is consistent with estimates from models that fit the IR-radio correlation in compact starburst galaxies.

Nyckelord: galaxies: individual (Arp220), galaxies: starburst, ISM: supernova remnants



Denna post skapades 2011-10-24. Senast ändrad 2014-09-02.
CPL Pubid: 147648

 

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