A Quasar-Galaxy Mixing Diagram: Quasar Spectral Energy Distribution Shapes in the Optical to Near-Infrared

TL;DR

This paper introduces a mixing diagram based on spectral energy distribution slopes to distinguish quasar, galaxy, and reddening effects, and applies it to analyze a large sample of AGN, revealing insights into their host galaxy contributions and evolutionary stages.

Contribution

The study presents a novel mixing diagram method to classify and analyze quasar SEDs, effectively estimating host galaxy fraction and reddening, and explores AGN evolutionary stages.

Findings

The mixing diagram distinguishes quasar, galaxy, and reddening-dominated SEDs.

The E94 quasar SED effectively describes a wide range of AGN properties.

Outliers in the diagram may indicate different AGN evolutionary stages.

Abstract

We define a quasar-galaxy mixing diagram using the slopes of their spectral energy distributions (SEDs) from 1\mu m to 3000\AA\ and from 1\mu m to 3\mu m in the rest frame. The mixing diagram can easily distinguish among quasar-dominated, galaxy-dominated and reddening-dominated SED shapes. By studying the position of the 413 XMM selected Type 1 AGN in the wide-field "Cosmic Evolution Survey" (COSMOS) in the mixing diagram, we find that a combination of the Elvis et al. (1994, hereafter E94) quasar SED with various contributions from galaxy emission and some dust reddening is remarkably effective in describing the SED shape from 0.3-3\mu m for large ranges of redshift, luminosity, black hole mass and Eddington ratio of type 1 AGN. In particular, the location in the mixing diagram of the highest luminosity AGN is very close (within 1\sigma) to that of the E94 SED. The mixing diagram can also be used to estimate the host galaxy fraction and reddening in quasar. We also show examples of some outliers which might be AGN in different evolutionary stages compared to the majority of AGN in the quasar-host galaxy co-evolution cycle.