@article {2013ApJ...764...42S, title = {{Submillimeter Interferometry of the Luminous Infrared Galaxy NGC 4418: A Hidden Hot Nucleus with an Inflow and an Outflow}}, journal = {The Astrophysical Journal}, volume = {764}, year = {2013}, month = {feb}, pages = {42}, abstract = {We have observed the nucleus of the nearby luminous infrared galaxy NGC 4418 with subarcsec resolution at 860 and 450 {$μ$}m for the first time to characterize its hidden power source. A \~{}20 pc (0.{\textquoteright}{\textquoteright}1) hot dusty core was found inside a 100 pc scale concentration of molecular gas at the galactic center. The 860 {$μ$}m continuum core has a deconvolved (peak) brightness temperature of 120-210 K. The CO(3-2) peak brightness temperature there is as high as 90 K at 50 pc resolution. The core has a bolometric luminosity of about 10$^{11}$ L $_{\&sun;}$, which accounts for most of the galaxy luminosity. It is Compton thick (N $_{H}$ {\gt}\~{} 10$^{25}$ cm$^{-2}$) and has a high luminosity-to-mass ratio (L/M) \~{} 500 L $_{\&sun;}$ M $_{\&sun;}$ $^{-1}$ as well as a high luminosity surface density 10$^{8.5 {\textpm} 0.5}$ L $_{\&sun;}$ pc$^{-2}$. These parameters are consistent with an active galactic nucleus to be the main luminosity source (with an Eddington ratio about 0.3), while they can be also due to a young starburst near its maximum L/M. We also found an optical color (reddening) feature that we attribute to an outflow cone emanating from the nucleus. The hidden hot nucleus thus shows evidence of both an inflow, previously seen with absorption lines, and the new outflow reported here in a different direction. The nucleus must be rapidly evolving with these gas flows.}, keywords = {galaxies: active, galaxies: evolution, galaxies: individual: NGC 4418, galaxies: ISM}, doi = {10.1088/0004-637X/764/1/42}, url = {http://adsabs.harvard.edu/abs/2013ApJ...764...42S}, author = {Sakamoto, K. and Aalto, S. and F. Costagliola and Mart{\'\i}n, S. and Ohyama, Y. and Wiedner, M.~C. and Wilner, D.~J.} } @article {2011A\&A...527A.150L, title = {{A survey of HC$_{3}$N in extragalactic sources. Is HC$_{3}$N a tracer of activity in ULIRGs?}}, journal = {Astronomy and Astrophysics}, volume = {527}, year = {2011}, month = {mar}, pages = {A150}, 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 {\textquoteright}{\textquoteright}HC$_{3}$N-luminous galaxy{\textquoteright}{\textquoteright} 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. Appendix is only available in electronic form at http://www.aanda.org}, keywords = {galaxies: active, galaxies: ISM, galaxies: starburst, ISM: molecules, radio lines: galaxies, radio lines: ISM}, doi = {10.1051/0004-6361/201015565}, url = {http://adsabs.harvard.edu/abs/2011A\%26A...527A.150L}, author = {Lindberg, J.~E. and Aalto, S. and F. Costagliola and P{\'e}rez-Beaupuits, J.-P. and Monje, R. and Muller, S.} }