Discovery of Carbon Radio Recombination Lines in M82
Review article, 2014
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.
radio lines: ISM
radio lines: galaxies
galaxies: individual (M82)
galaxies: ISM
ISM: general
Author
L. K. Morabito
Leiden University
J. B. R. Oonk
Netherlands Institute for Radio Astronomy (ASTRON)
Leiden University
F. Salgado
Leiden University
M. C. Toribio
Netherlands Institute for Radio Astronomy (ASTRON)
H. Rottgering
Leiden University
Aggm Tielens
Leiden University
R. Beck
Max Planck Society
B. Adebahr
Max Planck Society
P. Best
Royal Observatory
R. Beswick
University of Manchester
A. Bonafede
University of Hamburg
G. Brunetti
Istituto di Radioastronomia
M. Brüggen
University of Hamburg
K.T. Chyz̊y
Jagiellonian University in Kraków
John Conway
Chalmers, Earth and Space Sciences, Onsala Space Observatory
W. van Driel
Paris Diderot University
J. Gregson
Open University
M. Haverkorn
Leiden University
Radboud University
G. Heald
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
Cathy Horellou
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
A. Horneffer
Max Planck Society
M. Iacobelli
Netherlands Institute for Radio Astronomy (ASTRON)
M. J. Jarvis
University of Oxford
University of the Western Cape
Ivan Marti-Vidal
Chalmers, Earth and Space Sciences, Onsala Space Observatory
G. Miley
Leiden University
D. D. Mulcahy
University of Southampton
E. Orru
Netherlands Institute for Radio Astronomy (ASTRON)
Radboud University
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
A. M. M. Scaife
University of Southampton
Eskil Varenius
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
R. J. van Weeren
Harvard-Smithsonian Center for Astrophysics
G. J. White
RAL Space/STFC
Open University
M. W. Wise
Netherlands Institute for Radio Astronomy (ASTRON)
Astrophysical Journal Letters
2041-8205 (ISSN) 2041-8213 (eISSN)
Vol. 795 2 Art. no. L33- L33Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1088/2041-8205/795/2/l33