HNC and HCN in Seyfert Galaxies

¹ Kapteyn Astronomical Institute, Rijksuniversiteit Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
² Onsala Rymdobservatorium, Chalmers Tekniska Högskola, Sweden
³ SRON Netherlands Institute for Space Research, The Netherlands

Corresponding author: jp@astro.rug.nl

Abstract

What are the physical conditions in the nuclear region of Seyfert galaxies? Can we asses the predominant nuclear source of power starburst or AGN by using high density gas tracers? We have used SEST, JCMT, and IRAM 30 m telescopes to observe the J = 1–0, J = 3–2, and J = 4–3 transition lines of HNC and HCN in the Seyfert 2 galaxies NGC 1068 and NGC 3079. We model the excitatioon conditions of these molecules based on the observed 3–2/1–0 line intensity ratios. In these proceedings we show the line ratios and discuss the excitation conditions modeled. We summarize our results and conclusions as follows: in NGC 1068, the emission of HNC emerges from lower (< 10⁵ cm^-3) density gas than HCN (> 10⁵ cm^-3). Instead, the emission of HNC and HCN emerges from the same gas in NGC 3079. The observed HCN/HNC line ratios favor a PDR scenario rather than an XDR one. However, the N(HNC)/N(HCN) column density ratios obtained for NGC 3079 can be found only in XDR environments.