Nuclear stellar discs (NSDs), of a few tens to hundreds of parsec across, are a common and yet poorly studied feature of early-type galaxies. Still, such small discs represent a powerful tool to constrain the assembling history of galaxies, since they can be used to trace to the epoch when galaxies experienced their last major merger event. By studying the fraction and stellar age of NSDs, it is thus possible to test the predictions for the assembly history of early-type galaxies according to the current hierarchical paradigm for galaxy formation. In this paper we have produced the most comprehensive census of NSDs in nearby early-type galaxies by searching for such discs in objects within 100 Mpc and by using archival images from the Hubble Space Telescope. We found that NSDs are present in approximately 20 per cent of early-type galaxies, and that the fraction of galaxies with NSDs depends neither on their Hubble type nor on their galactic environment, whereas the incidence of NSDs appears to decline in the most massive systems. Furthermore, we have separated the light contribution of 12 such discs from that of their surrounding stellar bulge in order to extract their physical properties. This doubles the number of decomposed NSDs and although the derived values for their central surface brightness and scalelength are consistent with previous studies, they also give a hint of possible different characteristics due to different formation scenario between nuclear discs and other kinds of large galactic discs

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Approximately 20% of early-type galaxies host small nuclear stellar discs that are tens to a few hundred parsecs in size. Such discs are expected to be easily disrupted during major galactic encounters, hence their age serve to constrain their assembly history. We use VIMOS integral-field spectroscopic observations for the intermediate-mass E0 galaxy NGC 4458 and age-date its nuclear disc via high-resolution fitting of various model spectra. We find that the nuclear disc is at least 6 Gyr old. A clue to gain narrow limits to the stellar age is our knowledge of the nuclear disc contribution to the central surface brightness. The presence of an old nuclear disk, or the absence of disruptive encounters since z ∼ 0.6, for a small galaxy such as NGC 4458 which belongs to the Virgo cluster, may be consistent with a hierarchical picture for galaxy formation where the smallest galaxies assembles earlier and the crowded galactic environments reduce the incidence of galaxy mergers. On the other hand, NGC 4458 displays little or no bulk rotation except for a central kpc-scale kinematically-decoupled core. Slow rotation and decoupled core are usually explained in terms of mergers. The presence and age of the nuclear disc constraint these mergers to have happened at high redshift.

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