Far-ultraviolet flux distribution in Orion and its relation to stellar accretion

Context. Orion is the closest region hosting active star formation and young OBA stars. Accurately determining the far-ultraviolet (FUV) flux at its stellar population is essential to connect stellar and protoplanetary disc properties to the environment. Aims. We (1) accurately estimated the FUV flux and its distribution at a numerous stellar population of Orion by statistically accounting for the uncertainty in parallax measurements, and (2) investigated the relation between stellar accretion and external FUV radiation field by comparing observations and disc evolution models. Methods. We selected a large stellar population in Orion (within a 6 degrees radius of the Orion Nebula Cluster core), assigned sub-cluster memberships, and used the two-dimensional sub-cluster geometry to infer three-dimensional separations from OBA stars and compute the FUV flux (and its uncertainty) at each stellar position. We studied the accretion luminosities (L-acc) inferred from H-alpha emission in Gaia XP spectra of Orion sources and determined their detection fraction as a function of age and FUV flux. We compared the results with population synthesis models of viscous discs experiencing external photoevaporation. Results. We provided a publicly available table of FUV fluxes at similar to 8600 stars in Orion. Most of this stellar population is weakly FUV irradiated, <10(2) G(0), similar to 35% is intermediately irradiated, 10(2)-10(4) G(0), and only similar to 5% has FUV fluxes >10(4) G(0). Gaia-based L-acc decreases with age, and H-alpha detection fraction declines more rapidly in regions with strong FUV fluxes (greater than or similar to 10(2) G(0)) than in regions exposed to weaker FUV fluxes (less than or similar to 10(2) G(0)), broadly consistent with the model. This result may suggest that external photoevaporation efficiently depletes strongly FUV irradiated accretion discs, but it is not sufficient to reliably confirm this conclusion. Conclusions. The tools we provided for accurately computing FUV fluxes at the Orion stellar population will be essential for targeting sources in future observations aimed at assessing the role of external photoevaporation on protoplanetary disc. Our study highlights the need for additional measurements of stellar and disc properties across the Orion population, covering the FUV flux range 1-10(5) G(0).