2011A&A...527A.150L

HC₃N is a molecule that is mainly associated with Galactic star-forming regions, but it has also been detected in extragalactic environments. 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, CII flux, and megamaser activity). 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. 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 CII flux.