A survey of HC₃N in extragalactic sources

Abstract

Context. HC 3 N 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 HC 3 N, when combining earlier data from the literature with six new single-dish detections, and to compare HC 3 N 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 HC 3 N rotational lines (mainly the J = 10-9 transition) and of the J =1-0 transitions of HCN and HNC. Our combined HC 3 N 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 "HC 3 N-luminous galaxy" is made based upon the HC 3 N/HCN ratio. Most (∼80%) HC 3 N-luminous galaxies seem to be deeply obscured galaxies and (U)LIRGs. A majority (∼60% or more) of the HC 3 N-luminous galaxies in the sample present OH mega-or strong kilomaser activity. A possible explanation is that both HC 3 N and OH megamasers need warm dust for their excitation. Alternatively, the dust that excites the OH megamaser offers protection against UV destruction of HC 3 N. A high silicate absorption strength is also found in several of the HC 3 N-luminous objects, which may help the HC 3 N to survive. Finally, we find that a high HC 3 N/HCN ratio is related to a high dust temperature and a low C ii flux.

HC3N observations of nearby galaxies

“…While the HC 3 N survey by Lindberg et al (2011) did not observe NGC 660, its 10−9 and 12−11 transitions were not detected by Costagliola et al (2011). This difference in the detection of HC 3 N lines may imply that there is little warm and dense gas content in NGC 660, thus the high-J HC 3 N lines can not be excited.…”

“…In contrast, the high-J lines of other dense molecular gas tracers such as HCN and HCO + are at very high frequencies, and it is therefore difficult to observe them with ground-based telescopes. Another advantage of using HC 3 N lines is that HC 3 N is very likely optically thin even in low-J transitions, due to the relatively low abundance (Irvine et al 1987;Lindberg et al 2011); low opacity is important for accurate estimate of dense molecular gas mass for the study of the relationship between dense molecular gas and star formation (Gao & Solomon 2004a,b;Wang et al 2011;Zhang et al 2014). …”

“…Observations suggest that HC 3 N is related to the warm, dense, star-forming gas, and is easily dissociated by UV radiation (Henkel et al 1988;Costagliola et al 2011;Lindberg et al 2011;Aladro et al 2011Aladro et al , 2015. HC 3 N was found to be unusually luminous in NGC 4418, and it A&A 600, A15 (2017) (2) and (3) coordinates; (4) heliocentric velocities; (5) distances; (6) total infrared luminosities (from Sanders et al 2003); (7) CO 1−0 line width (FWHM) of the galaxies; and (8) the telescope these galaxies were observed with.…”

Molecules atz= 0.89

“…HC 3 N emission has also been detected in several extragalactic objects (see Lindberg et al 2011 for a recent review).…”

Spatially Resolved Chemistry in Nearby Galaxies. Ii. The Nuclear Bar in Maffei 2

“…Much observational and theoretical effort has been dedicated to understanding these diagnostic species in nearby starbursts (e.g. Henkel et al 1991;Nguyen-Q-Rieu et al 1992;Solomon, Downes, & Radford 1992;Helfer & Blitz 1993;Kohno et al 2001;Aalto et al 2002;Gao & Solomon 2004;Imanishi et al 2007;Baan et al 2008;Graciá-Carpio et al 2008;Juneau et al 2009;Bayet et al 2009;Lindberg et al 2011;Aladro et al 2011a). Unfortunately interpreting these results can be difficult since most of these studies have been done at low spatial resolution, either with single-dish telescopes or in distant sources.…”