Chemical complexity in NGC1068

TL;DR

This study investigates the molecular chemistry of NGC1068's circumnuclear region, identifying key molecules and comparing its chemical environment with starburst galaxies, revealing the influence of X-rays, shocks, UV radiation, and cosmic rays.

Contribution

It provides the first detection of several molecules in NGC1068 and introduces the CH3CCH/HC3N ratio as a new indicator of starburst and AGN influences.

Findings

Detection of 24 molecular species, including 7 new in NGC1068.

The CH3CCH/HC3N ratio varies significantly among galaxies, indicating different environmental effects.

Shocks and X-rays both influence the chemistry of NGC1068.

Abstract

We aimed to study the chemistry of the circumnuclear molecular gas of NGC1068, and to compare it with those of the starburst galaxies M82 and NGC253. Using the IRAM-30m telescope, we observed the inner 2 kpc of NGC1068 between 86.2 GHz and 115.6 GHz. We identified 35 spectral features, corresponding to 24 different molecular species. Among them, HC3N, SO, N2H+, CH3CN, NS, 13CN, and HN13C are detected for the first time in NGC1068. Assuming local thermodynamic equilibrium (LTE), we calculated the column densities of the detected molecules, as well as the upper limits to the column densities of some undetected species. The comparison among the chemistries of NGC1068, M82, and NGC253, suggests that, apart from X-rays, shocks also determine the chemistry of NGC1068. We propose the column density ratio between CH3CCH and HC3N as a prime indicator of the imprints of starburst and AGN environments in the circumnuclear interstellar medium. This ratio is, at least, 64 times larger in M82 than in NGC1068, and, at least, 4 times larger in NGC253 than in NGC1068. Finally, we used the UCL_CHEM and UCL_PDR chemical codes to constrain the origin of the species, as well as to test the influence of UV radiation fields and cosmic rays on the observed abundances.