Red halos and extragalactic background light

TL;DR

The paper suggests that the unusually red halos observed around disk galaxies in optical and near-IR wavelengths may be due to extinction of the extragalactic background light, offering an alternative explanation to stellar population models.

Contribution

It proposes that extinction of the extragalactic background light explains the red halo colors, challenging previous explanations based on stellar populations, metallicity, or dust.

Findings

Red halos' colors may result from extragalactic background light extinction.

Extinction effects can account for color anomalies without invoking high metallicity.

Combining star counts and surface photometry can measure the extragalactic background light.

Abstract

Deep surface photometry of disk galaxies at optical and near-IR wavelengths have revealed faint halos with colours much too red to be reconciled with the resolved stellar populations detected in the halos of the Milky Way or M31. Alternative scenarios involving high metallicities, nebular emission or large amounts of dust in these halos are also disfavoured. Here, we argue that extinction of the optical extragalactic background light in the halos of these galaxies may possibly be responsible for the reported colour anomalies. We also discuss how an independent measurement of the optical extragalactic background light might be accomplished by combining direct star counts with surface photometry for a single nearby galaxy.