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Discovery of Carbon Radio Recombination Lines in M82

L. K. Morabito ; J. B. R. Oonk ; F. Salgado ; M. C. Toribio ; H. J. A. Rottgering ; Aggm Tielens ; R. Beck ; B. Adebahr ; P. Best ; R. Beswick ; A. Bonafede ; G. Brunetti ; M. Bruggen ; K. T. Chyzy ; John Conway (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; W. van Driel ; J. Gregson ; M. Haverkorn ; G. Heald ; Cathy Horellou (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; A. Horneffer ; M. Iacobelli ; M. J. Jarvis ; Ivan Marti-Vidal (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium) ; G. Miley ; D. D. Mulcahy ; E. Orru ; R. Pizzo ; A. M. M. Scaife ; Eskil Varenius (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; R. J. van Weeren ; G. J. White ; M. W. Wise
Astrophysical Journal Letters (2041-8205). Vol. 795 (2014), 2, p. Art. no. L33.
[Artikel, refereegranskad vetenskaplig]

Carbon radio recombination lines (RRLs) at low frequencies (less than or similar to 500 MHz) trace the cold, diffuse phase of the interstellar medium, which is otherwise difficult to observe. We present the detection of carbon RRLs in absorption in M82 with the Low Frequency Array in the frequency range of 48-64 MHz. This is the first extragalactic detection of RRLs from a species other than hydrogen, and below 1 GHz. Since the carbon RRLs are not detected individually, we cross-correlated the observed spectrum with a template spectrum of carbon RRLs to determine a radial velocity of 219 km s(-1). Using this radial velocity, we stack 22 carbon-alpha transitions from quantum levels n = 468-508 to achieve an 8.5 sigma detection. The absorption line profile exhibits a narrow feature with peak optical depth of 3x10(-3) and FWHM of 31 km s(-1). Closer inspection suggests that the narrow feature is superimposed on a broad, shallow component. The total line profile appears to be correlated with the 21 cm Hi line profile reconstructed from Hi absorption in the direction of supernova remnants in the nucleus. The narrow width and centroid velocity of the feature suggests that it is associated with the nuclear starburst region. It is therefore likely that the carbon RRLs are associated with cold atomic gas in the direction of the nucleus of M82.

Nyckelord: galaxies: individual (M82), galaxies: ISM, ISM: general, radio lines: galaxies, radio lines: ISM



Denna post skapades 2015-01-05. Senast ändrad 2015-01-08.
CPL Pubid: 209544

 

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