Universe opacity and EBL

TL;DR

This paper models how galactic and intergalactic dust absorption affects the extragalactic background light (EBL), showing that universe opacity significantly influences EBL estimates and luminosity density evolution.

Contribution

It introduces a realistic dusty universe model that aligns EBL estimates with observations and explains luminosity density trends without star formation rate evolution.

Findings

EBL estimates range from 100 to 200 nW/m^2/sr, matching observations.

Luminosity density peaks at redshift 2-3, driven by universe volume changes.

Universe opacity increases with redshift, affecting high-z luminosity density.

Abstract

The observed extragalactic background light (EBL) is affected by light attenuation due to absorption of light by galactic and intergalactic dust in the Universe. Even galactic opacity of 10-20 percent and minute universe intergalactic opacity of $0.01\,\mathrm{mag}\,h\,\mathrm{Gpc}^{-1}$ at the local Universe have a significant impact on the EBL because obscuration of galaxies and density of intergalactic dust increase with redshift as $\left(1+z\right)^3$. Consequently, intergalactic opacity increases and the Universe becomes considerably opaque at $z > 3$. Adopting realistic values for galactic and intergalactic opacity, the estimates of the EBL for the expanding dusty universe are close to observations. The luminosity density evolution fits well measurements. The model reproduces a steep increase of the luminosity density at $z<2$, its maximum at $z=2-3$, and its decrease at higher redshifts. The increase of the luminosity density at low $z$ is not produced by the evolution of the star formation rate but by the fact that the Universe occupied a smaller volume in previous epochs. The decline of the luminosity density at high $z$ originates in the opacity of the Universe. The calculated bolometric EBL ranges from 100 to 200 $\mathrm{n W m}^{-2}\mathrm{sr}^{-1}$ and is within the limits of 40 and 200 $\mathrm{n W m}^{-2}\mathrm{sr}^{-1}$ of current EBL observations. The model predicts 98\% of the EBL coming from radiation of galaxies at $z<3.5$. Accounting for light extinction by intergalactic dust implies that the Universe was probably more opaque than dark for $z>3.5$.