Using a complete spectroscopic survey to find red quasars and test the KX method

TL;DR

This study uses a comprehensive spectroscopic survey combining IRIS2 imaging and the Fornax Cluster Spectroscopic Survey to identify red quasars and evaluate the effectiveness of the KX selection method across diverse quasar colours.

Contribution

It introduces a new quasar sample with measured colours and demonstrates the KX method's superiority over UVX and optical selection techniques in detecting red quasars.

Findings

Red quasars constitute at least 22% of the quasar population.

The KX method outperforms UVX in quasar detection.

Red quasars have significantly different colour distributions from previous surveys.

Abstract

We present an investigation of quasar colour-redshift parameter space in order to search for radio-quiet red quasars and to test the ability of a variant of the KX quasar selection method to detect quasars over a full range of colour without bias. This is achieved by combining IRIS2 imaging with the complete Fornax Cluster Spectroscopic Survey to probe parameter space unavailable to other surveys. We construct a new sample of 69 quasars with measured bJ - K colours. We show that the colour distribution of these quasars is significantly different from that of the Large Bright Quasar Survey's quasars at a 99.9% confidence level. We find 11 of our sample of 69 quasars have signifcantly red colours (bJ - K >= 3.5) and from this, we estimate the red quasar fraction of the K <= 18.4 quasar population to be 31%, and robustly constrain it to be at least 22%. We show that the KX method variant used here is more effective than the UVX selection method, and has less colour bias than optical colour-colour selection methods.