Study of HCN/CO intensity ratio around AGN using ALMA data

ABSTRACT :
We focus on the effect of active galactic nuclei (AGN)on interstellar matter to understand galaxy evolution. The dense gas tracer HCN(J=1-0) and molecular gas tracer CO(J=1-0) has been commonly used to study physical properties of molecular gas around AGN. We observed the nearby Seyfert galaxy NGC 1068 with ALMA to study dense molecular gas around the AGN. NGC 1068 has a circumnuclear disk (CND) (radius ~0.2 kpc) surrounding the AGN. The HCN(1-0)/CO(1-0) intensity ratio map of NGC 1068 with the highest resolution and highest sensitivity compared to previous studies was created. The HCN/CO intensity ratio was higher than the typical value for star-forming galaxies (0.1: e.g., Casasola et al. 2011) not only for CND but also for a position 0.3 kpc away from CND.
Anomalous excitation and/or anomalous abundance ratios are one of the likely causes. The excitation anomaly could be a maser, but no sign of it was obtained from the spectra.