The filled red circles correspond to the cross-correlation between the new DR7 QSO sample in Boötes and the 100 $\micron$ map. The horizontal dotted line marks the zero signal expected if there is no correlation between quasars and cirrus. The vertical dashed line corresponds to the FWHM of the IRAS beam. Data points below the scale of the IRAS beam are strongly correlated. For the DR9 quasars, the cross-correlation with the 100 $\micron$ maps in the HeLMS S82 region exhibits a systematic negative signal. Data points from different fields are shifted slightly horizontally for visual clarity.[]{data-label="fig:qso_iris_all"}](dr9_allfields_100_scramble.eps "fig:"){height="2.7in" width="3.45in"}

![Cross-correlation between DR9 QSOs and 100 $\micron$ maps in the HeRS S82 (top) and HeLMS S82 (bottom) region. Different coloured symbols represent cross-correlation signal computed using DR9 quasars with different $i$-band apparent magnitude cut (corrected for Galactic extinction) (red dots: $i$-band cut = 21.2; green dots: 21.0; blue dots: 20.0). We have not used the “uniform $>0$” criterion in the samples plotted here. The anti-correlation in the HeLMS S82 region seen in Fig. \[fig:qso\_iris\_all\] has more or less disappeared. The horizontal dotted line corresponds to zero correlation. The vertical dashed line corresponds to the FWHM of the IRAS beam. Data points below 