The Contribution from Scattered Light to Quasar Galaxy Hosts

TL;DR

This paper models how scattering of quasar light by electrons and dust in host galaxies can significantly affect observed properties, complicating the interpretation of quasar host galaxy data.

Contribution

It introduces models showing scattering can account for observed extended flux in quasar hosts, highlighting its impact on inferred galaxy properties.

Findings

Scattering can produce high ratios of nuclear to extended flux.

Scattered light can lead to overestimates of host galaxy luminosity and mass.

Scattering may explain observed luminosity peaks and galaxy morphology trends.

Abstract

We present models representing the scattering of quasar radiation off free electrons and dust grains in geometries that approximate the structure of quasar host galaxies. We show that, for reasonable assumptions, scattering alone can easily produce ratios of nuclear (point source) to extended fluxes comparable to those determined in studies of quasar hosts. This result suggests that scattered quasar light, as well as stellar emission from the host galaxy, contributes significantly to the detected extended flux, leading to uncertainty in the inferred properties of quasar host. A significant contribution from scattered quasar light will lead to overestimates of the luminosity and hence mass of the host galaxy, and may also distort its morphology. Scattering of quasar light within the host galaxy may provide alternative explanations for the apparent peak in host luminosity at z = 2-3; possibly the overall average higher luminosity of radio-loud host galaxies relative to those of radio-quiet quasars (RQQs), and the apparent preference of high-luminosity RQQs for spheroidal rather than disk galaxies.