Finding growing supermassive black holes (i.e., active galactic nuclei or AGN) is a key component of understanding how galaxies evolve and to understanding the likely mergers of those supermassive black holes. AGN identification is a difficult task, with the most well-understood tracers of black hole growth being affected by obscuration due to dust and gas. In “A Hard X-ray Test of HCN Enhancements as a Tracer of Embedded Black Hole Growth” (Privon+) we test the use of a proposed millimeter-wave AGN indicator (the HCN/HCO+ line ratio) by looking for hard X-ray emission in a set of galaxies. We find that the HCN/HCO+ line ratio is not a reliable way of identifying current AGN. We also collect data from the literature and look at whether the HCN/HCO+ line ratio is empirically linked to the AGN luminosity or the fraction of the total luminosity which is emitted by the AGN. There is no evidence that these (sub)millimeter line ratios trace the current level of black hole growth. The paper has been accepted for publication in The Astrophysical Journal and a preprint is available at the link above.
Update (24 April 2020): The article is now published in The Astrophysical Journal as Privon et al. 2020 ApJ 893 149.