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Issue A&A
Volume 435, Number 3, June I 2005
Page(s) 831 - 837
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041825



A&A 435, 831-837 (2005)
DOI: 10.1051/0004-6361:20041825

Radio recombination lines from the starburst galaxy NGC 3256

A. L. Roy1, 2, 3, 4, 5, W. M. Goss4, Niruj R. Mohan6 and K. R. Anantharamaiah5

1  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
    e-mail: aroy@mpifr-bonn.mpg.de
2  Geodätisches Institut der Universität Bonn, Nussallee 17, 53115 Bonn, Germany
3  Australia Telescope National Facility, PO Box 76, Epping 1710, NSW, Australia
4  NRAO, PO Box O, Socorro, NM 87801, USA
5  Raman Research Institute, CV Raman Ave, Sadashivanagar, Bangalore 560080, India
6  Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France

(Received 10 August 2004 / Accepted 14 February 2005)

Abstract
We have detected the radio recombination lines H91$\alpha$ and H92$\alpha$ with rest frequencies of 8.6 GHz and 8.3 GHz from the starburst nucleus NGC 3256 at an angular resolution of 16.4'' $\times$ 9.6'' using the Australia Telescope Compact Array and at an angular resolution of 12.0'' $\times$ 2.9'' using the VLA. The line was detected at ~1 mJy beam-1 peak with a width of 160 km s-1 with the ATCA and at ~0.5 mJy beam-1 peak with a width of 114 km s-1 with the VLA. Modelling the line emitting region as a collection of H II regions, we derive constraints on the required number of H II regions, their temperature, density, and distribution. We find that a collection of 10 to 300 H II regions with temperatures of 5000 K, densities of 1000 cm-3 to 5000 cm-3 and diameters of 15 pc produced good matches to the line and continuum emmission. The Lyman continuum production rate required to maintain the ionization is 2 $\times$ $10^{52}~{\rm s}^{-1}$ to 6 $\times$ $10^{53}~{\rm s}^{-1}$, which requires 600 to 17 000 O5 stars to be produced in the starburst.


Key words: galaxies: individual: NGC 3256 -- galaxies: nuclei -- radio lines: galaxies

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© ESO 2005


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