Refine
Has Fulltext
- no (2)
Year of publication
- 2004 (2) (remove)
Document Type
- Article (2)
Language
- English (2)
Is part of the Bibliography
- yes (2)
Institute
We investigate multicolour imaging data of a complete sample of 19 low-redshift (z < 0.2) quasar host galaxies. The sample was imaged in four optical (BVRi) and three near-infrared bands (JHK(s)). Galaxy types, structural parameters and robust host galaxy luminosities are extracted for all bands by means of two-dimensional deblending of galaxy and nucleus. For the disc-dominated fraction of host galaxies (Sa and later) the optical and optical-to-near-infrared colours agree well with the average colours of inactive galaxies of the same type. The bulge-dominated galaxies (E/S0), on the other hand, appear a significant 0.3 mag bluer in (V-K) than their inactive counterparts, being as blue as the discs in the sample. This trend is confirmed by fitting population synthesis models to the extracted broad-band spectral energy distributions: the stellar population age of the bulge-dominated hosts lies around a few Gyr, much younger than expected for old evolved ellipticals. Comparison to other studies suggests a strong trend for stellar age in elliptical host galaxies with luminosity. Intermediately luminous elliptical hosts have comparably young populations, either intrinsically or from an enhanced star formation rate potentially due to interaction; the most luminous and massive ellipticals on the contrary show old populations. The correspondence between the nuclear activity and the blue colours suggests a connection between galaxy interaction, induced star formation and the triggering of nuclear activity. However, the existence of very symmetric and undisturbed discs and elliptical host galaxies emphasized that other mechanisms like minor merging or gas accretion must exist
We describe an algorithm to decompose deep images of active galactic nuclei into host galaxy and nuclear components. Currently supported are three galaxy models: a de Vaucouleurs spheroidal; an exponential disc; and a two- component disc + bulge model. Key features of the method are: (semi-)analytic representation of a possibly spatially variable point spread function; full two-dimensional convolution of the model galaxy using gradient-controlled adaptive subpixelling; and a multiple iteration scheme. The code is computationally efficient and versatile for a wide range of applications. The quantitative performance is measured by analysing simulated imaging data. We also present examples of the application of the method to small test samples of nearby Seyfert 1 galaxies and quasars at redshifts z < 0.35