Revisiting the local interstellar radiation field using Gaia DR3

INAF-Osservatorio Astrofisico di Arcetri, L. E. Fermi 5, 50125 Firenze, Italy

^★ Corresponding author; simone.bianchi@inaf.it

Received: 12 June 2024
Accepted: 24 September 2024

Abstract

Context. Dust grains in the interstellar medium are heated by the integrated radiation from stars in the Milky Way. Thus, knowledge of the local interstellar radiation field (LISRF) is necessary to interpret observations of dust emission in the infrared and constrain (some) properties of interstellar grains. The LISRF representation that is most widely used in dust modeling still dates back to the seminal works of Mezger et al. (1982, A&A, 105, 372) and Mathis et al. (1983, A&A, 128, 212).

Aims. A new version of the LISRF is presented here, starting from the photometry of the Gaia Data Release 3 (DR3) and revisiting the available data. This dataset includes observations from the Pioneer 10 and 11 probes.

Methods. The LISRF contribution by direct starlight was estimated in the Gaia bands by summing fluxes of all stars in DR3. The LISRF was extrapolated from the optical to the ultraviolet and near-infrared, using the astrophysical parameters provided by DR3 for a subsample of Gaia stars. The correlation between dust emission at 100 µm and residual diffuse emission in the Pioneer and other available maps was exploited to derive the contribution of dust-scattered starlight to the LISRF.

Results. The new LISRF is significantly redder and emits ~30% more energy than the old model. The old LISRF is almost a factor two lower in the near-infrared, while, in the optical, it accounts only for direct starlight. For |b| < 50°, diffuse starlight contributes on average to ~25% of the total radiation, which is three times more than what can be derived using literature estimates at high Galactic latitudes.

Conclusions. The new LISRF can modify the predicted mid-infrared (MIR) dust emission beyond the uncertainties normally assumed between dust models and observational constraints. These differences should be taken into account to redefine the properties of small grains and of carriers of the MIR emission bands.