AKARI SPECTROSCOPY OF QUASARS AT 2.5 - 5 MICRON

Abstract

Utilizing a unique capability of AKARI that allows deep spectroscopy at <TEX>$2.5-5.0{\mu}m$</TEX>, we performed a spectroscopy study of more than 200 quasars through one of the AKARI mission programs, QSONG (Quasar Spectroscopic Observation with NIR Grism). QSONG targeted 155 high redshift (3.3 < z < 6.42) quasars and 90 low redshift active galactic nuclei (0.002 < z < 0.48). In order to provide black hole mass estimates based on the rest-frame optical spectra, the high redshift part of QSONG is designed to detect the <TEX>$H{\alpha}$</TEX> line and the rest-frame optical spectra of quasars at z > 3.3. The low redshift part of QSONG is geared to uncover the rest-frame <TEX>$2.5-5.0{\mu}m$</TEX> spectral features of active galactic nuclei to gain useful information such as the dust-extinction-free black hole mass estimators based on the Brackett lines and the temperatures of the hot dust torus. We outline the program strategy, and present some of the scientific highlights from QSONG, including the detection of the <TEX>$H{\alpha}$</TEX> line from a quasar at z > 4.5 which indicates a rigorous growth of black holes in the early universe, and the <TEX>$Br{\beta}$</TEX>-based black hole mass estimators and the hot dust temperatures (~ 1100 K) of low redshift AGNs.