Cosmoglobe DR2. IV. Modelling starlight in DIRBE with Gaia and WISE

TL;DR

This paper develops a detailed model of starlight emission in DIRBE data using Gaia and WISE measurements, accurately accounting for bright and faint sources to improve understanding of infrared background signals.

Contribution

It introduces a novel Bayesian framework combining Gaia and WISE data to model starlight emission in DIRBE observations, including both bright and faint sources.

Findings

Stars account for 91% of flux at 2.2μm

Faint sources contribute significantly at longer wavelengths

Model supports precise measurements of cosmic infrared background

Abstract

We present a model of starlight emission in the Diffuse Infrared Background Explorer (DIRBE) data between 1.25 and 25$\,\mu$m based on \textit{Gaia} and WISE measurements. We include two classes of compact objects, namely bright stars with individual spectral energy densities (SEDs) measured by \textit{Gaia}, and a combined diffuse background of dim point source emission. Of the 424\ 829 bright sources that we fit, the number of stars with a flux density detected by WISE at Galactic latitudes $|b|>20^{\circ}$ at more than $5\,\sigma$ is 94\,680, for an average of 1.36~stars per DIRBE beam area. For each star, we adopt physical parameters ($T_{\mathrm{eff}}$, $\log g$, and [M/H]) from \textit{Gaia}; use these to identify a best-fit effective SED with the PHOENIX stellar model library; convolve with the respective DIRBE bandpass; and fit an overall free amplitude per star within the Bayesian end-to-end \texttt{Cosmoglobe} DR2 framework. The contributions from faint sources are accounted for by coadding all 710\ 825\ 587 WISE sources not included as bright stars, and fit one single overall amplitude per DIRBE band. Based on this model we find that total star emission accounts for 91\,\% of the observed flux density at 2.2\,$\mu$m; 54\,\% at 4.9$\,\mu$m; and 1\,\% at 25\,$\mu$m. As shown in companion papers, this new model is sufficiently accurate to support high-precision measurements of both the Cosmic Infrared Background monopole and zodiacal light emission in the three highest DIRBE frequencies.