2010MNRAS.408..713W

There is increasing evidence of a connection between active galactic nuclei (AGN) activity and galaxy evolution. To obtain further insight into this potentially important evolutionary phase, we analyse the properties of quasar host galaxies. In this paper, we present a population synthesis modelling technique for off-axis spectra, the results of which constrain host colour and the stellar ages of luminous quasars [M_V(nuc) < -23]. Our technique is similar to well-established quiescent-galaxy models, modified to accommodate scattered nuclear light (a combination of atmospheric, instrumental and host galaxy scattered light) observed off axis. In our model, the subtraction of residual scattered quasar light is performed, while simultaneously modelling the constituent stellar populations of the host galaxy. The reliability of this technique is tested via a Monte Carlo routine in which the correspondence between synthetic spectra with known parameters and the model output is determined. Application of this model to a preliminary sample of 10 objects is presented and compared to previous studies. Spectroscopic data were obtained via long-slit and integral-field unit observations on the Keck and Wisconsin Indiana Yale and NOAO (WIYN) telescopes. We confirm that elliptical quasar hosts are distinguishable (bluer) from inactive ellipticals in rest-frame B - V colour. Additionally, we note a trend for radio luminous (L_5GHz ≳ 10⁴⁰erg/s) quasars to be located in redder host galaxies in comparison to their less luminous radio counterparts. While the host colour and age of our radio luminous sample are in close proximity to the green valley, our radio faint sample is consistent with quiescent star-forming galaxies. However, further observations are needed to confirm these results. Finally, we discuss future applications for our technique on a larger sample of objects being obtained via Southern African Large Telescope (SALT) and WIYN telescope observing campaigns.