Dense circum-nuclear molecular gas in starburst galaxies

TL;DR

This study investigates dense molecular gas in the circum-nuclear regions of nine starburst galaxies, analyzing its properties, kinematics, and the influence of starbursts and active galactic nuclei using molecular line observations.

Contribution

It provides detailed observations of dense molecular gas and identifies photon dominated regions in starburst galaxy nuclei, offering new insights into their interstellar medium.

Findings

Detection of HCN and HCO$^{+}$ in most galaxies

Identification of PDRs in several galaxy nuclei

Unusual HNC emission in NGC 5236

Abstract

We present results from a study of the dense circum-nuclear molecular gas of starburst galaxies. The study aims to investigate the interplay between starbursts, active galactic nuclei and molecular gas. We characterise the dense gas traced by HCN, HCO$^{+}$ and HNC and examine its kinematics in the circum-nuclear regions of nine starburst galaxies observed with the Australia Telescope Compact Array. We detect HCN (1$-$0) and HCO$^{+}$ (1$-$0) in seven of the nine galaxies and HNC (1$-$0) in four. Approximately 7 arcsec resolution maps of the circum-nuclear molecular gas are presented. The velocity integrated intensity ratios, HCO$^{+}$ (1$-$0)/HCN (1$-$0) and HNC (1$-$0)/HCN (1$-$0), are calculated. Using these integrated intensity ratios and spatial intensity ratio maps we identify photon dominated regions (PDRs) in NGC 1097, NGC 1365 and NGC 1808. We find no galaxy which shows the PDR signature in only one part of the observed nuclear region. We also observe unusually strong HNC emission in NGC 5236, but it is not strong enough to be consistent with X-ray dominated region (XDR) chemistry. Rotation curves are derived for five of the galaxies and dynamical mass estimates of the inner regions of three of the galaxies are made.