Modeling the Cosmic Ultraviolet Background at the North Galactic Pole

TL;DR

This paper models the dust-scattered component of the Cosmic Ultraviolet Background at the North Galactic Pole, fitting observations to derive dust properties and identify an unexplained isotropic offset.

Contribution

It develops a parametric model for dust-scattered UV light as a function of reddening and applies it to GALEX data to estimate dust properties and background offsets.

Findings

Dust-scattered emission scales linearly with reddening up to E(B-V) ≈ 0.1 mag.

Derived dust grain properties are consistent with the Astrodust model.

Detected an isotropic UV background offset of 267 ± 7 units, partly unexplained.

Abstract

I explore models of the dust-scattered component of the Cosmic Ultraviolet Background (CUVB) at the North Galactic Pole (NGP) in order to develop a framework for calculating the dust-scattered light as a function of the optical depths. As expected, I find that the dust-scattered emission scales linearly with reddening up to $E(B-V) \approx 0.1$\ mag and derive a parametric model for this dependence. I have applied these models to fit the far-ultraviolet (1350--1800 \AA) observations from the \textit{Galaxy Evolution Explorer (GALEX)} finding that the optical constants of the interstellar dust grains -- albedo ($a$) and phase function asymmetry factor ($g$) -- are consistent with predictions from the Astrodust model ($a = 0.33$, $g = 0.68$). I detect an isotropic offset of $267 \pm 7$ ph cm$^{-2}$ s$^{-1}$ sr$^{-1}$ \AA$^{-1}$, half of which remains unaccounted for by known Galactic or extragalactic sources. I will now extend my analysis to wider sky regions with the goal of generating high-resolution extinction maps.