Searching for Compact Obscured Nuclei in Compton-thick Active Galactic Nuclei

June 2025 • 2025ApJ...985..259J

Authors • Johnstone, Makoto A. • Privon, George C. • Barcos-Muñoz, Loreto • Evans, A. S. • Aalto, S. • Armus, Lee • Bauer, Franz E. • Blecha, L. • Gallagher, J. S. • König, S. • Ricci, Claudio • Treister, Ezequiel • Eibensteiner, Cosima • Emig, Kimberly L. • Green, Kara N. • Kunneriath, Devaky • Nagarajan-Swenson, Jaya • Saravia, Alejandro • Yoon, Ilsang

Abstract • Compact obscured nuclei (CONs) are heavily obscured infrared cores that have been found in local (ultra-)luminous infrared galaxies. They show bright emission from vibrationally excited rotational transitions of HCN, known as HCN-vib, and are thought to harbor Compton-thick (CT, N_H ≥ 10²⁴ cm^‑2) active galactic nuclei (AGNs) or extreme compact starbursts. We explore the potential evolutionary link between CONs and CT-AGNs by searching for CONs in hard-X-ray-confirmed CT-AGNs from the Great Observatories All-sky LIRG Survey (GOALS). Here, we present new Atacama Large Millimeter/submillimeter Array Band 6 observations that targeted HCN-vib emission in four hard-X-ray-confirmed CT-AGNs. We analyze these objects together with literature HCN-vib measurements of five additional hard-X-ray-confirmed CT-AGNs from the GOALS sample. We do not detect any CONs in this combined sample of nine CT-AGNs. We then explore a proposed evolutionary sequence in which CONs evolve into X-ray-detectable CT-AGNs once outflows and feedback reduce the column densities of the enshrouding gas. We find, however, no evidence of well-developed dense molecular outflows in the observed CT-AGNs. While this could suggest that CT-AGNs are not universally linked to CONs, it could also be explained by a short duty cycle for molecular outflows.

Links

• PDF https://iopscience.iop.org/article/10.3847/1538-4357/adcecb/pdf
• PREPRINT http://arxiv.org/abs/2504.15248
• ELECTR https://doi.org/10.3847/1538-4357/adcecb