\begin{table}%t2
\caption{Pool of control quasars used in the present investigation (see Sect.~2).
The first 20~quasars are shown. The full table is available in electronic form at the CDS 
(see also {\tt http://\protect adlibitum.oats.inaf.it/ vladilo/tables.html}).}\label{tab2}
\small%\centerline
 {
\begin{tabular}{cccr}
\hline \hline
SDSS & $z_{\rm e}$ & $m_{\rm r}$ & {\it SNR}$^a$ \\
 & & [mag] & \\
\hline
073512.52+292017.0 & 2.26 & 19.44 &     6 \\ 
105703.34+051141.5 & 2.27 & 19.44 &     5 \\ 
152715.82+491833.4 & 2.27 & 18.19 &    13 \\ 
104129.27+563023.5 & 2.27 & 18.98 &     9 \\ 
141123.51+004252.9 & 2.27 & 18.06 &    15 \\ 
091209.59-000954.9 & 2.27 & 19.13 &     9 \\ 
131902.33+432235.1 & 2.27 & 18.70 &    11 \\ 
085424.97+543938.7 & 2.27 & 18.84 &    10 \\ 
150158.36+365348.5 & 2.27 & 18.96 &     8 \\ 
160216.74+293038.8 & 2.27 & 18.69 &    11 \\ 
005202.39+010129.3 & 2.27 & 17.40 &    53 \\ 
105852.64+000917.8 & 2.27 & 18.79 &    10 \\ 
140108.59+381417.0 & 2.27 & 19.09 &    12 \\ 
151932.72+481349.9 & 2.27 & 18.87 &     9 \\ 
100636.44+050031.0 & 2.27 & 19.20 &     8 \\ 
153013.94+580802.4 & 2.28 & 18.05 &    18 \\ 
094702.76+321818.4 & 2.27 & 19.73 &     6 \\ 
150806.89+005610.3 & 2.28 & 18.01 &    16 \\ 
123435.50+540323.9 & 2.28 & 18.33 &    14 \\ 
110914.13-003600.7 & 2.28 & 18.96 &    13 \\ 
\hline
\end{tabular}}
\smallskip%\medskip
$^a$ Mean signal-to-noise ratio in the rest-frame spectral window 1440$-$1490~\AA. 
\end{table}