A survey of HC3N in extragalactic sources
Is HC3N a tracer of activity in ULIRGs?⋆
Centre for Star and Planet Formation, Natural History Museum of Denmark,
University of Copenhagen,
Øster Voldgade 5-7,
2 Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Santa Cruz de Tenerife, Spain
3 Department of Earth and Space Sciences, Onsala Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden
4 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
5 Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
6 California Institute of Technology, 1200 E. California Blvd., Mail Code 301-17, Pasadena, CA 91125-4700, USA
Received: 11 August 2010
Accepted: 16 December 2010
Context. HC3N is a molecule that is mainly associated with Galactic star-forming regions, but it has also been detected in extragalactic environments.
Aims. To present the first extragalactic survey of HC3N, when combining earlier data from the literature with six new single-dish detections, and to compare HC3N with other molecular tracers (HCN, HNC), as well as other properties (silicate absorption strength, IR flux density ratios, C ii flux, and megamaser activity).
Methods. We present mm IRAM 30 m, OSO 20 m, and SEST observations of HC3N rotational lines (mainly the J = 10–9 transition) and of the J = 1–0 transitions of HCN and HNC. Our combined HC3N data account for 13 galaxies (excluding the upper limits reported for the non-detections), while we have HCN and HNC data for more than 20 galaxies.
Results. A preliminary definition “HC3N-luminous galaxy” is made based upon the HC3N/HCN ratio. Most (~80%) HC3N-luminous galaxies seem to be deeply obscured galaxies and (U)LIRGs. A majority (~60% or more) of the HC3N-luminous galaxies in the sample present OH mega- or strong kilomaser activity. A possible explanation is that both HC3N and OH megamasers need warm dust for their excitation. Alternatively, the dust that excites the OH megamaser offers protection against UV destruction of HC3N. A high silicate absorption strength is also found in several of the HC3N-luminous objects, which may help the HC3N to survive. Finally, we find that a high HC3N/HCN ratio is related to a high dust temperature and a low C ii flux.
Key words: galaxies: ISM / galaxies: starburst / galaxies: active / radio lines: galaxies / radio lines: ISM / ISM: molecules
Appendix is only available in electronic form at http://www.aanda.org
© ESO, 2011