redshifts and by young spheroids at high redshifts. With the data base available for that work, nearly the totality of DLAs at $z > 1.5$ are explained as spheroid systems formed in the redshift range 1.7$<$z$<$4.5, with masses between 10$^9$ and 10$^{10}$ M$_{\odot}$ and typical specific star formation rates of 1 to 3 Gyr$^{-1}$, where the definition of specific star formation is given in the footnote below[^6]. These objects might have taken part in merger processes that then lead to bulges. It is possible that the most massive of them, those with N$_{\rm HI} \approx 10^{22}$ cm$^{-2}$, could be proto-bulges.

Zinc has played a special role in estimations of the metallicity of DLAs (Pettini et al. 1990, 1994, 1997; Akerman et al. 2005). That Zn is non-refractory guarantees that it is not heavily depleted in the ISM. On the observational side, Zn has two strong transitions at 2026 and 2062 [Å]{}, which almost always lie outside the Ly-$\alpha$ forest and are rarely saturated owing to their low oscillator strengths and low Zn abundances. Given that Zn is only a trace element that contributes $\approx 10^{-4}$ of the mass density for the heavy elements, and because of the weakness of the 