Physical Properties of Luminous Dust Poor Quasars
  We identify and characterize a population of luminous dust poor quasars at
0<z<5, similar in photometric properties to the objects found at z>6
previously. This class of active galactic nuclei has been known to show little
IR emission from a dusty structure, but is yet poorly understood in terms of
number evolution or of dependence on physical quantities. In order to better
understand the luminous dust poor quasar properties, we compiled a rest-frame
UV to IR library of 41,000 optically selected type-1 quasars with
$L_{bol}>10^{45.7} erg s^{-1}$. After fitting the broad-band spectral energy
distributions (SEDs) with accretion disk and dust components, we find 0.6% of
our sample to be hot dust poor with a rest-frame 2.3 micron to 0.51 micron flux
density ratio of -0.5 dex or less. The dust poor SEDs are blue in the
UV-optical and weak in the MIR, such that their accretion disks are less
obscured, and that hot dust emission traces that of warm dust down to the dust
poor regime. At a given bolometric luminosity, dust poor quasars are lower in
black hole mass and higher in Eddington ratio than general luminous quasars,
suggesting that they are in a rapidly growing evolutionary state in which the
dust poor phase appears as a short or rare phenomenon. The dust poor fraction
increases with redshift, and possible implications for the evolution of the
dust poor fraction are discussed.
