Properties of spectrally-defined red QSOs at z = 0.3-1.2
  We investigated the properties of a sample of red Quasi-stellar Objects
(QSOs) using optical, radio, and infrared data. These QSOs were selected from
the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) quasar catalog. We only
selected sources with sky coverage of the Very Large Array Faint Images of the
Radio Sky at Twenty-centimeters (VLA FIRST) survey, and searched for sources
with Wide-field Infrared Survey Explorer (WISE) counterparts. We defined the
spectral color of the QSOs based on the flux ratio of the rest frame 4000$\AA$
to 3000$\AA$ continuum emission to select red QSOs and typical QSOs. In
accordance with this criterion, only QSOs with redshifts between 0.3 and 1.2
could be selected. We found that the red QSOs have stronger infrared emission
than the typical QSOs do. We noted that the number ratios of the red QSOs to
the typical QSOs decrease with increasing redshifts, although the number of the
typical QSOs increase with redshifts. Furthermore, at high redshifts, the
luminosity distributions of the typical QSOs and the red QSOs seem to have
similar luminosity distribution peaks; however, at low redshifts, the
luminosities of the red QSOs seem to be lower than those of the typical QSOs.
These findings suggest that there might be at least two types of red QSOs in
our QSO samples.
