A sensitive submillimetre survey of broad absorption‐line quasars

Using the Submillimetre Common‐User Bolometer Array on the JCMT, we have carried out a submillimetre (submm) survey of broad absorption‐line quasars (BALQs). The sample has been chosen to match, in redshift and optical luminosity, an existing benchmark 850‐μm sample of radio‐quiet quasars, allowing a direct comparison of the submm properties of BAL quasars relative to the parent radio‐quiet population. We reach a submm limit 1σ≈ 1.5 mJy at 850 μm, allowing a more rigorous measure of the submm properties of BAL quasars than previous studies. Our submm photometry complements extensive observations at other wavelengths, in particular X‐rays with Chandra and infrared with Spitzer . To compare the 850‐μm flux distribution of BALQs with that of the non‐BAL quasar benchmark sample, we employ a suite of statistical methods, including survival analysis and a novel Bayesian derivation of the underlying flux distribution. Although there are no strong grounds for rejecting the null hypothesis that BALQs on the whole have the same submm properties as non‐BAL quasars, we do find tentative evidence (1–4 per cent significance from a Kolmogorov–Smirnov test and survival analysis) for a dependence of submm flux on the equivalent width of the characteristic C  iv BAL. If this effect is real – submm activity is linked to the absorption strength of the outflow – it has implications either for the evolution of active galactic nuclei (AGNs) and their connection with star formation in their host galaxies, or for unification models of AGNs.