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

TL;DR

The paper develops a comprehensive Bayesian framework within Cosmoglobe DR2 to model starlight in DIRBE data (1.25–25 μm) using Gaia-derived stellar parameters and WISE-derived diffuse backgrounds. It treats two stellar populations—424,829 bright stars with per-star SEDs from PHOENIX models and a diffuse background from the remaining WISE sources—jointly with other sky components, employing Gibbs sampling to infer amplitudes. The results show that stellar emission accounts for 91% of the 2.2 μm flux, 54% at 4.9 μm, and 1% at 25 μm, enabling high-precision measurements of the CIB monopole and zodiacal light; the work also provides detailed maps, SEDs, and extinction assessments. This integrated star model advances a unified, full-sky infrared/microwave sky model and improves constraints on the cosmic infrared background by more accurately removing stellar contamination. The authors discuss limitations (extinction treatment, beam shape) and outline concrete avenues for future enhancements, including 3D extinction modelling and incorporating additional high-frequency data.

Abstract

We present a model of starlight emission in the Diffuse Infrared Background Explorer (DIRBE) data between 1.25 and 25$\,μ$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 $5\,σ$ 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\,$μ$m; 54\,\% at 4.9$\,μ$m; and 1\,\% at 25\,$μ$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.

Figures (15)

• Figure 1: Top: Total number of bright sources in each pixel. Bottom: Total number of sources included in the diffuse template, which shows a clear imprint of the WISE scan strategy.
• Figure 2: Schematic diagram of the Cosmoglobe DR2 compact object processing pipeline. Red ovals represent input data, and the blue boxes indicate the two classes of sources described in this paper.
• Figure 3: Histograms of the three star parameters taken from Gaia (from top to bottom: effective temperature, gravitational acceleration, and metallicity) that are used by the PHOENIX database to determine the star SEDs, for the 424829 bright stars used in this analysis.
• Figure 4: Comparison of PHOENIX spectra for different parameter compbinations. In each panel the black curve shows a reference star spectrum with $T_{\mathrm{eff}}= 6000$K, $\log g = 3.0$ and $[M/H]= 0.0$. The colored curve shows, from top to bottom, the resulting spectra when setting $T_\mathrm{eff}=10000\mathrm{K}$, $\log g = 5.0$, and $[M/H]= -2.0$. The spectra shown in the middle panel have been smoothed to highlight the broad features that are mostly relevant for the current analysis.
• Figure 5: Ratio between the PHOENIX spectra shown in the middle panel of Fig. \ref{['fig:catalogueSEDs']}, corresponding to $E(\log g = 5)/E(\log g = 3)$. The vertical dashed lines indicate the positions of the six shortest wavelength DIRBE channels.