Primitive asteroids in the main belt, Cybele, and Hilda populations from Gaia DR3

Abstract: Primitive asteroids include C-, P-, and D-classes, known to be dark and having spectra mostly featureless. They differ in the spectral slope, which ranges from moderate values for C-types, and progressively increases in P- and D-types, the latter being the reddest. While C- and P-types are commonly observed in the asteroid main belt, D-types are commonly found further from the Sun, in the Cybele, Hilda, and Jupiter Trojans regions, and very few are reported in the main belt. This study aims at characterizing the abundance of primordial and red asteroids, belonging to the P-, D-, and Z-classes in the Mahlke et al. (2022) taxonomy, in the 2-5.2 AU region using the third data release by the Gaia mission spectral catalog, which includes more than 60000 spectrophotometric data of asteroids. We have applied the following methodology to identify primordial asteroids in the catalog: 1) selection of objects with signal to noise ratio greater than 20; 2) albedo value less than 12%; 3) chi-squared fit to automatically identify potential D-, Z-, and P-types using Bus-DeMeo and Mahlke taxonomy; 4) visual inspection of every spectrum to confirm the taxonomic classification. Referring to Mahlke taxonomy, we have found 318 new D-types across the main belt, as well as 124 Z-types, and is in agreement with theoretical estimations. We computed the spectral slope in the visible range (0.55 - 0.81 μm). We also have identified 265 P-types in the main belt. For the Cybele and Hilda asteroids, we characterize the taxonomic class of all the bodies with SNR higher than 20 in the Gaia catalog, for a total sample of 193 and 180 asteroids, respectively.