is uncorrelated with the noise properties of the SPIRE maps. For the DR9 QSOs in Boötes and [*XMM*]{}-LSS, we use the angular completeness masks used in White et al. (2012) and the MANGLE software (Swanson et al. 2008) to calculate the angular completeness of the survey, which is the fraction of quasar targets in a sector for which a spectrum was obtained. For the DR9 QSOs in the HeRS and HeLMS S82 region, we simply generate uniformly distributed points as the simulated QSO sample. The total number of simulated quasars $N_{S}$ is generally over 25 times larger than the total number of real quasars $N_{\rm Q}$.

We estimate errors on the two-point angular cross-correlation function by using 100 bootstrap samples of the quasar sample in each field. The bootstrap samples which have the same size as the real QSO sample are generated by sampling with replacement the real QSO sample. The dispersion in the signal between the bootstrap quasar samples and the SPIRE maps or the IRIS maps is taken as the error on the measured cross-correlation signal (Norberg et al. 2009).

![Cross-correlation between the SDSS DR7 (top) and SDSS-III DR9 (bottom) QSOs and the 100 $\micron$ maps. Different coloured 