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Title: DISCOVERY OF CARBON RADIO RECOMBINATION LINES IN M82

Carbon radio recombination lines (RRLs) at low frequencies (≲ 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{sup –1}. Using this radial velocity, we stack 22 carbon-α transitions from quantum levels n = 468-508 to achieve an 8.5σ detection. The absorption line profile exhibits a narrow feature with peak optical depth of 3 × 10{sup –3} and FWHM of 31 km s{sup –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 H I line profile reconstructed from H I absorption in the direction of supernova remnants in the nucleus. The narrow width and centroid velocity of the feature suggests that it is associated withmore » 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.« less
Authors:
; ; ; ; ;  [1] ; ;  [2] ; ;  [3] ;  [4] ;  [5] ; ;  [6] ;  [7] ;  [8] ; ;  [9] ;  [10] ;  [11] more »; « less
  1. Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)
  2. Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo (Netherlands)
  3. MPI für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)
  4. SUPA, Institute for Astronomy, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)
  5. Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom)
  6. Hamburg Observatory, University of Hamburg, Gojenbergsweg 112, D-21029 Hamburg (Germany)
  7. INAF-Istituto di Radioastronomia, Via P. Gobetti 101, I-40129 Bologna (Italy)
  8. Obserwatorium Astronomiczne Uniwersytetu Jagiellońskiego, ul. Orla 171, 30-244 Kraków (Poland)
  9. Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala (Sweden)
  10. GEPI, Observatoire de Paris, UMR 8111, CNRS, Université Paris Diderot, 5 Place Jules Janssen, F-92190 Meudon (France)
  11. Department of Physical Sciences, The Open University, Milton Keynes MK7 6AA (United Kingdom)
Publication Date:
OSTI Identifier:
22364500
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 795; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ABSORPTION SPECTRA; CARBON; DETECTION; GALAXIES; GHZ RANGE; HYDROGEN; MHZ RANGE; RADIAL VELOCITY; RECOMBINATION; SUPERNOVA REMNANTS