  In the context of charge-coupled devices (CCDs), the ultraviolet (UV) region
has mostly remained unexplored after the 1990s. Gaia DR3 offers the community a
unique opportunity to explore tens of thousands of asteroids in the near-UV as
a proxy of the UV absorption. This absorption has been proposed in previous
works as a diagnostic of hydration, organics, and space weathering. Aims. In
this work, we aim to explore the potential of the NUV as a diagnostic region
for primitive asteroids using Gaia DR3. We used a corrective factor over the
blue part of Gaia spectra to erase the solar analog selection effect. We
identified an artificial relation between the band noise and slope and applied
a signal-to-noise ratio (S/N) threshold for Gaia bands. Meeting the quality
standards, we employed a Markov chain Monte Carlo (MCMC) algorithm to compute
the albedo threshold, maximizing primitive asteroid inclusion. Utilizing one-
and two-dimensional (1D and 2D) projections, along with
dimensionality-reduction methods (such as PCA and UMAP), we identified
primitive asteroid populations. We uncovered: (a) the first observational
evidence linking UV absorption to the 0.7 {\mu}m band, tied to hydrated
iron-rich phyllosilicates; and (b) a 2D space revealing a split in C-type
asteroids based on spectral features, including UV absorption. The computed
average depth (3.5 +- 1.0 %) and center (0.70 +- 0.03 {\mu}m) of the 0.7 {\mu}m
absorption band for primitive asteroids observed with Gaia is in agreement with
the literature values. In this paper, we shed light on the importance of the UV
absorption feature to discriminate among different mineralogies (i.e.,
iron-rich phyllosilicates vs. iron-poor) or to identify taxonomies that are
conflated in the visible (i.e., F-types vs. B-types). We have shown that this
is a promising region for diagnostic studies of the composition of primitive
asteroids.
