UV density diagram for the thin- (top panel) and thick-disk (bottom panel) white dwarf population within 100 pc from the Sun. A clear overdensity is revealed in the thick-disk population (delimited by a red rectangle). For comparative purposes, we show the thin-disk dispersion ellipsoid for 1σ (continuous line) and 3σ (dashed line) levels corresponding to the thin-disk population (Torres et al. 2019), and we illustrate the number density (right scales) of white dwarf stars per 1 × 1 (km s)⁻². The location of the Hercules substreams from Antoja et al. (2012) is shown with red crosses. See text for details.