First Stellar Velocity Dispersion Measurement of a Luminous Quasar Host with Gemini North Laser Guide Star Adaptive Optics

TL;DR

This study demonstrates the first stellar velocity dispersion measurement of a luminous quasar host galaxy using Gemini North's laser guide star adaptive optics, revealing discrepancies with established galaxy-black hole relations.

Contribution

It introduces a novel application of LGS AO and integral field spectroscopy to measure stellar velocity dispersion in a luminous quasar host, achieving higher precision than previous methods.

Findings

Measured velocity dispersion of 217+/-15 km/s for PG1426+015

Discovered the galaxy's velocity dispersion exceeds the M-sigma relation for similar systems

Achieved higher measurement precision with shorter observation time

Abstract

We present the first use of the Gemini North laser guide star adaptive optics (LGS AO) system and an integral field unit (IFU) to measure the stellar velocity dispersion of the host of a luminous quasar. The quasar PG1426+015 (z=0.086) was observed with the Near-Infrared Integral Field Spectrometer (NIFS) on the 8m Gemini North telescope in the H-band as part of the Science Verification phase of the new ALTAIR LGS AO system. The NIFS IFU and LGS AO are well suited for host studies of luminous quasars because one can achieve a large ratio of host to quasar light. We have measured the stellar velocity dispersion of PG1426+015 from 0.1'' to 1'' (0.16 kpc to 1.6 kpc) to be 217+/-15 km/s based on high signal-to-noise ratio measurements of Si I, Mg I, and several CO bandheads. This new measurement is a factor of four more precise than a previous measurement obtained with long-slit spectroscopy and good, natural seeing, yet was obtained with a shorter net integration time. We find that PG1426+015 has a velocity dispersion that places it significantly above the M-sigma relation of quiescent galaxies and lower-luminosity active galactic nuclei with black hole masses estimated from reverberation mapping. We discuss several possible explanations for this discrepancy that could be addressed with similar observations of a larger sample of luminous quasars.