Infrared 3-4 Micron Spectroscopy of Nearby PG QSOs and AGN-Nuclear Starburst Connections in High-luminosity AGN Populations

TL;DR

This study uses infrared spectroscopy to analyze nuclear starburst activity in high-luminosity PG QSOs, revealing consistent AGN-starburst connections across different luminosities and supporting models linking black hole growth to starburst-induced turbulence.

Contribution

It provides the first infrared spectroscopic evidence of nuclear starbursts in high-luminosity PG QSOs and compares their properties with lower-luminosity AGNs, confirming the universality of AGN-starburst relations.

Findings

Detected 3.3 micron PAH emission in 5 out of 30 PG QSOs.

Nuclear-starburst-to-AGN luminosity ratios are similar across luminosity ranges.

Results support models linking black hole growth to starburst activity.

Abstract

We present the results of infrared L-band (3-4 micron) slit spectroscopy of 30 PG QSOs at z < 0.17, the representative sample of local high-luminosity, optically selected AGNs. The 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission feature is used to probe nuclear (< a few kpc) starburst activity and to investigate the connections between AGNs and nuclear starbursts in PG QSOs. The 3.3 micron PAH emission is detected in the individual spectra of 5/30 of the observed PG QSOs. We construct a composite spectrum of PAH-undetected PG QSOs and discern the presence of the 3.3 micron PAH emission therein. We estimate the nuclear-starburst and AGN luminosities from the observed 3.3 micron PAH emission and 3.35 micron continuum luminosities, respectively, and find that the nuclear-starburst-to-AGN luminosity ratios in PG QSOs are similar to those of previously studied AGN populations with lower luminosities, suggesting that AGN-nuclear starburst connections are valid over the wide luminosity range of AGNs in the local universe. The observed nuclear-starburst-to-AGN luminosity ratios in PG QSOs with available supermassive black hole masses are comparable to a theoretical prediction based on the assumption that the growth of a supermassive black hole is controlled by starburst-induced turbulence.