STRUCTURE IN HOST GALAXIES OF STEEP-SPECTRUM RADIO QSOS

We present deep imaging in two bands of five high-luminosity steep-spectrum radio QSOs. The set of broadband filters we have used has been specifically designed to exclude contamination from all strong emission lines found in extended emission regions around QSOs. For four of the objects, we also have deep R-band imaging. Because we generally do not have suitable stars for determining the point-spread function within our limited fields, we have developed a simple technique for detecting asymmetric structure close to the QSO by using a rotational average of the QSO profile itself. This technique allows us to examine the region immediately surrounding the QSO, and we have successfully detected at least one new galaxy and several other features not evident on our original images. All five objects show either close companions or substantial host-galaxy asymmetries; these results support the view that interactions are important in luminous QSOs, but the lack of a suitable control sample prevents our giving quantitative statistical substance to this statement. Companion galaxies span the whole available color range, while diffuse extensions from two of the QSOs are both quite blue; this last result, however, could well be the result of observational bias.