AAS 203rd Meeting, January 2004
Session 105 Dwarf, Irregular, LUM IR and Starburst Galaxies
Oral, Wednesday, January 7, 2004, 2:00-3:30pm, Regency VII

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[105.01] High Angular Resolution (~1'') Observations of Extragalactic Radio Recombination Lines at Low (8.3 GHz) and High (~ 43 GHz) Frequencies

C. A. Rodriguez-Rico (CRyA - UNAM), W. M. Goss (NRAO), F. Viallefond (Observatoire de Paris), J. H. Zhao (CfA)

The on-set of the star formation in the starburst galaxies is not fully understood. Radio recombination lines are necessary to study the starburst phenomena when dust absorption is dominant at optical and infrared frequencies. Using observations of different recombination lines from hydrogen and continuum observations at different frequencies, it is possible to compute the physical parameters (e.g. electronic temperature, density and size) that characterize the HII regions located in the starburst regions. Moreover, the velocity field of the ionized gas is observed using radio recombination lines in the central regions of the starburst galaxies. Then, sensitive high angular resolution observations of the recombination line emission are necessary.

M82 and NGC 253 are two of the nearest (~3 Mpc) and brightest starburst galaxies and then were excellent candidates to observe the radio recombination lines H92\alpha and H53\alpha. Arp 220 is a merger, the closest Ultraluminous Infrared Galaxy and the farthest (~73 Mpc) from which radio recombination lines have been observed. Given that Anantharamaiah et al. (2000) detected different radio recombination lines (up to mm frequencies) from Arp 220, it was an excellent candidate to observe the recombination line H53\alpha.

All the observations have been carried out using the Very Large Array given the high angular resolution (~1'') and sensitivity required. We present the results of these radio recombination lines and radio continuum observations toward M82, NGC 253 and Arp 220.

We are thankful to UNAM and CONACyT for its support to present these work.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.