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

Watson, L.C., Martini, P., Dasyra, K.M., Bentz, M.C., Ferrarese, L., Peterson, B.M., Pogge, R.W., Tacconi, L.J. 2008, ApJL, 682, L21

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 PG 1426+015 (z=0.086) was observed with the Near-Infrared Integral Field Spectrometer (NIFS) on the 8 m 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 PG 1426+015 from 0.1'' to 1'' (0.16 to 1.6 kpc) to be 217+/-15 km s-1 based on high signal-to-noise ratio measurements of Si I, Mg I, and several CO band heads. This new measurement is a factor of 4 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 PG 1426+015 has a velocity dispersion that places it significantly above the MBH-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.

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