Is there LFIR-LHCN correlation for low LFIR isolated galaxies?

Abstract

We observed HCN(1-0) in 15 well isolated galaxies where 9 galaxies were clearly detected. The aim of these observations is to confirm the relationship between the (dense) molecular gas and star formation (SF) activity through the correlation found by [3][4] between the FIR and HCN luminosity. We find that the detected galaxies in HCN(1-9) have a lower HCN luminosity than the expected from the FIR-HCN correlation. This departure from the correlation may be due to an extended emission of the HCN(1-0) line in the galaxies. To prove this we mapped 4 galaxies that were clearly detected in HCN(1-0) at the center of the galaxy to measure their spatial extension and to get a more precise measurement of the total HCN (1-0) luminosity. The HCN(1-0) luminosity was compared to the CO(1-0) luminosity finding a ratio that implies that de galaxies in the sample have a low level of activity.