Research
Dust reddened quasars
Radio galaxies
For many years, the only way of finding significant numbers of obscured quasars was by identifying the host galaxies of bright radio sources. Radio galaxies still provide important insights into both the nature of the obscured quasar evolution, and the formation of the most massive black holes known in the Universe.Mid-infrared selection of AGN and quasars
In recent years, a new geneneration of infrared and optical surveys have been able to find much larger numbers of dust obscured quasars. My research has concentrated on mid-infared selection using surveys from the Spitzer Space Telescope such as SWIRE as a basis. Luminous AGN and quasars separate well from star forming and quiescent galaxies in mid-infrared color space due to their strong hot dust continua. Spectroscopy with ground-based optical and near-infrared telescopes can then be used to find the redshift of the objects.Host galaxies with HST and adaptive optics
Studying the host galaxies of reddened quasars is useful for two reasons. First, the quasars themselves are much fainter in the rest-frame optical, allowing more details of the inner part of the host galaxy to be seen. Second, dust reddening is very likely to occur in quasars which are associated with recent merger events, thus, by studying the hosts of these objects we can investigate the links between quasar activity and galaxy mergers. For some samples see here.Very distant galaxies
Searches for H-alpha emission at z>7
H-alpha emission is one of the most well calibrated indicators of current star formation in galaxies, but beyond z~2.6 the H-alpha line is redshifted out of the near-infrared observing window. We are attempting to find, or place limits on, the H-alpha emission from z>7 galaxies using Spitzer, whose IRS spectrograph is sensitive to emission lines at >5 microns. These will be the only such attempts until the launch of JWST.Stellar populations of z~6 galaxies
The IRAC camera on Spitzer is capable of detecting galaxies out to z~6 and beyond, and the only instrument capable of seeing rest-frame optical emission from these galaxies. We hae been able to show that, even at z~6, many galaxies show evidence of relatively old stellar populations, suggesting their first bursts of star formation were at z>~8.
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