Millimeter recombination lines and the state of ionized gas in M82

Details Millimeter recombination lines and the state of ionized gas in M82 Millimeter recombination lines and the state of ionized gas in M82

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...429..612s&link_type=abstract

The Astrophysical Journal, vol. 429, no. 2, pt. 1, p. 612-617

Physics

Optics

12

Astronomical Models, Atomic Recombination, Electron Energy, Flux Density, H Lines, Ion Production Rates, Ionized Gases, Millimeter Waves, Starburst Galaxies, Acousto-Optics, Correction, Electric Choppers, Radio Telescopes, Spectrometers, Spontaneous Emission

Scientific paper

We report the detection of the H30alpha recombination line at 230 GHz (1.3 mm) in the nuclear region of the starburst galaxy M82. This is the highest frequency recombination line so far detected at radio wavelengths in an external galaxy. A comparison with recombination line data at other millimeter wavelengths shows the emission mechanism is predominantly spontaneous emission. By comparing the line emission with the underlying continuum, we derive an electron temperature of 4000 +/- 500 K, and the integrated flux density in the lines yields an ionization rate of 1.1 +/- 0.3 x 1054/sec. On the basis of a comparison between millimeter recombination and far-IR forbidden line data, we suggest that most of the recombination line emission occurs in dense star-forming clouds with densities of order 104/cm3, and filling factor approximately 10-4, whereas most of the forbidden line emission originates in a more massive lower density region. This picture removes the requirement in M82 for a restrictive range in stellar mass for the production of the ionizing photons, suggested by Puxley et al. The implication of this model is that the mass of ionized gas in the nucleus of M82 is 1.5 to 4.5 x 106 solar mass, an order of magnitude less than normally derived.

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