# Properties of spectrally-defined red QSOs at z = 0.3-1.2

## TL;DR

This study characterizes red QSOs at z=0.3-1.2 using optical, radio, and infrared data, revealing their stronger infrared emission and potential existence of two types based on redshift and luminosity differences.

## Contribution

It introduces a spectral color criterion for selecting red QSOs and compares their properties to typical QSOs across redshifts using multi-wavelength data.

## Key findings

- Red QSOs have stronger infrared emission than typical QSOs.
- The ratio of red to typical QSOs decreases with increasing redshift.
- Red QSO luminosities are lower at low redshift but similar at high redshift.

## Abstract

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.