Submillimetre Observations of hard X-ray selected Quasars

(Stevens)

We have been studying hard X-ray selected QSOs and their environments for more than a decade using a large variety of facilities (JCMT, Spitzer, UKIRT, WHT, XMM-Newton). A breakthrough result was the discovery that QSOs with hard X-ray spectra have higher star-formation rates than ordinary QSOs, providing a link between the obscured growth of black holes and the build-up of stellar mass (e.g. Page, Stevens, et al. 2001, Science, 294, 2516; Stevens et al., 2005, 360, 610).

We have since shown that the hard X-ray spectra are due to ionised absorbers which can be produced by an outflowing wind capable of terminating the star-formation (Page, Carrera, Stevens et al. 2011, 416, 2792). A related strand of this research concerns the environments of the QSOs; we find that they contain over-densities of star forming galaxies (e.g. Stevens et al. 2010, MNRAS, 405, 2623) most of which are likely associated with the QSO (Carrera, Page, Stevens et al. 2011, MNRAS, 413, 2791) and are likely to evolve into clusters of galaxies by the current epoch.

Current work focuses on a new sample of XMM-Newton selected QSOs which have higher absorbing column densities than the previous sample which was selected from ROSAT data. We are making observations of 20 of these QSOs with the new SCUBA-2 camera on the JCMT. The initial scientific goals are:

• To firm up the statistics on detection rate in comparison to our control sample of unabsorbed QSOs and to test whether FIR luminosity correlates with redshift.
• To search for trends between FIR luminosity and X-ray absorbing column density. A correlation might indicate that more highly obscured QSOs are caught in an earlier evolutionary phase, or alternatively that at least some of the X-ray obscuring material resides in the host galaxy and is connected to the star-formation process (a torus origin is unlikely because the absorbed QSOs are optically classified as type 1, i.e. they are viewed pole-on rather than through the torus).
• To search for over-densities of star-forming galaxies in the fields of the QSOs as a function of redshift to determine the evolution of structure formation in dense environments. The handful of objects mapped with SCUBA allowed us to establish that an excess of galaxies exists around the QSOs relative to the field but the study was limited in both area mapped and redshift range. The bright end of the number counts are poorly constrained due to the small area mapped while we were unable to say anything at all about evolution of environment with redshift.