HCN/HCO+ ratio for AGN

We analyse the behaviour of these ratios at varying resolutions and employ non-LTE radiative transfer models to infer the physical conditions that drive the observed ratios. We find that the HCN/HCO+ ratio from higher J transitions can differentiate between AGN and SB activity when observed at high spatial resolution. This distinction occurs around unity.

However, at lower resolutions, contamination from multiple emission sources and beam averaging effects destroy these distinctions. Modelling suggests that elevated HCN/HCO+ ratios in AGN-dominated regions are largely driven by an enhancement in HCN abundance relative to HCO+, likely due to high-temperature chemistry or increased excitation. Our study confirms that the HCN/HCO+ ratio, particularly of higher J transitions, can be a reliable tracer of AGN versus SB activity if observations are conducted at sufficiently high spatial resolution.