@article{KuhlbrodtOrndahlWisotzkietal.2005,
  author    = {Kuhlbrodt, B. and Orndahl, E. and Wisotzki, Lutz and Jahnke, Knud},
  title     = {High-redshift quasar host galaxies with adaptive optics},
  issn      = {0004-6361},
  year      = {2005},
  abstract  = {We present K band adaptive optics observations of three high-redshift ( z similar to 2.2) high-luminosity quasars, all of which were studied for the first time. We also observed several point spread function ( PSF) calibrators, non-simultaneously because of the small field of view. The significant temporal PSF variations on timescales of minutes inhibited a straightforward scaled PSF removal from the quasar images. Characterising the degree of PSF concentration by the radii encircling 20\% and 80\% of the total flux, respectively, we found that even under very different observing conditions the r(20) vs. r(80) relation varied coherently between individual short exposure images, delineating a well-defined relation for point sources. Placing the quasar images on this relation, we see indications that all three objects were resolved. We designed a procedure to estimate the significance of this result, and to estimate host galaxy parameters, by reproducing the statistical distribution of the individual short exposure images. We find in all three cases evidence for a luminous host galaxy, with a mean absolute magnitude of M-R = - 27.0 and scale lengths around similar to 4 - 12 kpc. Together with a rough estimate of the central black hole masses obtained from C.. line widths, the location of the objects on the bulge luminosity vs. black hole mass relation is not significantly different from the low-redshift regime, assuming only passive evolution of the host galaxy. Corresponding Eddington luminosities are L-nuc/L-Edd similar to 0.1 - 0.6},
  language  = {en}
}
@article{JahnkeKuhlbrodtWisotzki2004,
  author    = {Jahnke, Knud and Kuhlbrodt, B. and Wisotzki, Lutz},
  title     = {Quasar host galaxy star formation activity from multicolour data},
  issn      = {0035-8711},
  year      = {2004},
  abstract  = {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},
  language  = {en}
}
@article{KuhlbrodtWisotzkiJahnke2004,
  author    = {Kuhlbrodt, B. and Wisotzki, Lutz and Jahnke, Knud},
  title     = {Decomposition of active galactic nucleus host galaxy images},
  issn      = {0035-8711},
  year      = {2004},
  abstract  = {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},
  language  = {en}
}
@article{CourbinLetaweMagainetal.2002,
  author    = {Courbin, F. and Letawe, G. and Magain, P and Wisotzki, Lutz and Jablonka, P. and Alloin, Danielle and Jahnke, Knud and Kuhlbrodt, B. and Meylan, G. and Minniti, D.},
  title     = {Spectroscopy of quasar host galaxies at the VLT: stellar populations and dynamics down to the central kiloparsec},
  year      = {2002},
  language  = {en}
}
@article{CourbinLetaweMagainetal.2002,
  author    = {Courbin, F. and Letawe, G. and Magain, P. and Wisotzki, Lutz and Jablonka, P. and Jahnke, Knud and Kuhlbrodt, B. and Alloin, Danielle and Meylan, G. and Minniti, D. and Burud, Ingunn},
  title     = {On-axis spatially resolved spectroscopy of low redshift quasar host galaxies: HE 1503+0228, at z=0.135},
  year      = {2002},
  abstract  = {We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2 m ESO Very Large Telescope, Antu. The spectra are spatially deconvolved using a spectroscopic version of the ``MCS deconvolution algorithm''. The algorithm decomposes two dimensional spectra into the individual spectra of the central point-like nucleus and of its host galaxy. Applied to HE 1503+0228 at z=0.135 (MB=-23.0), it provides us with the spectrum of the host galaxy between 3600 {\AA} and 8500 {\AA} (rest-frame), at a mean resolving power of 700. The data allow us to measure several of the important Lick indices. The stellar populations and gas ionization state of the host galaxy of HE 1503+0228 are very similar to the ones measured for normal non-AGN galaxies. Dynamical information is also available for the gas and stellar components of the galaxy. Using deconvolution and a deprojection algorithm, velocity curves are derived for emission lines, from the center up to 4arcsec away from the nucleus of the galaxy. Fitting a simple three-components mass model (point mass, spherical halo of dark matter, disk) to the position-velocity diagram, we infer a mass of M(r<1 kpc) = (2.0 +/- 0.3)x 1010 Msun within the central kiloparsec of the galaxy, and a mass integrated over 10 kpc of M(r<10 kpc) = (1.9 +/- 0.3) x 1011 Msun, with an additional 10 \% error due to the uncertainty on the inclination of the galaxy. This, in combination with the analysis of the stellar populations indicates that the host galaxy of HE 1503+0228, is a normal spiral galaxy. Based on observations made with ANTU/UT1 at ESO-Paranal observatory in Chile (program 65.P-0361(A)), and with the ESO 3.5 m NTT, at La Silla observatory (program 62.P-0643(B)).},
  language  = {en}
}
@article{CourbinLetaweMagainetal.2002,
  author    = {Courbin, F. and Letawe, G. and Magain, P. and Wisotzki, Lutz and Jablonka, P. and Jahnke, Knud and Kuhlbrodt, B. and Alloin, Danielle and Meylan, G. and Minniti, D. and Burud, Ingunn},
  title     = {On-axis spatially resolved spectroscopy of low redshift quasar host galaxies: HE 1503+0228, at z=0.135},
  year      = {2002},
  abstract  = {We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2 m ESO Very Large Telescope, Antu. The spectra are spatially deconvolved using a spectroscopic version of the ``MCS deconvolution algorithm''. The algorithm decomposes two dimensional spectra into the individual spectra of the central point-like nucleus and of its host galaxy. Applied to HE 1503+0228 at z=0.135 (MB=-23.0), it provides us with the spectrum of the host galaxy between 3600 {\AA} and 8500 {\AA} (rest-frame), at a mean resolving power of 700. The data allow us to measure several of the important Lick indices. The stellar populations and gas ionization state of the host galaxy of HE 1503+0228 are very similar to the ones measured for normal non-AGN galaxies. Dynamical information is also available for the gas and stellar components of the galaxy. Using deconvolution and a deprojection algorithm, velocity curves are derived for emission lines, from the center up to 4arcsec away from the nucleus of the galaxy. Fitting a simple three- components mass model (point mass, spherical halo of dark matter, disk) to the position-velocity diagram, we infer a mass of M(r<1 kpc) = (2.0 +/- 0.3)x 1010 Msun within the central kiloparsec of the galaxy, and a mass integrated over 10 kpc of M(r<10 kpc) = (1.9 +/- 0.3) x 1011 Msun, with an additional 10\% error due to the uncertainty on the inclination of the galaxy. This, in combination with the analysis of the stellar populations indicates that the host galaxy of HE 1503+0228, is a normal spiral galaxy. Based on observations made with ANTU/UT1 at ESO-Paranal observatory in Chile (program 65.P-0361(A)), and with the ESO 3.5 m NTT, at La Silla observatory (program 62.P-0643(B)).},
  language  = {en}
}
@article{WisotzkiKuhlbrodtJahnke2001,
  author    = {Wisotzki, Lutz and Kuhlbrodt, B. and Jahnke, Knud},
  title     = {The luminosity function of QSO host galaxies},
  isbn      = {0-306-46662-7},
  year      = {2001},
  language  = {en}
}
@article{JahnkeKuhlbrodtOerndahletal.2001,
  author    = {Jahnke, Knud and Kuhlbrodt, B. and {\"O}rndahl, E. and Wisotzki, Lutz},
  title     = {QSO host galaxy star formation history from multicolour data},
  isbn      = {0-306-46662-7},
  year      = {2001},
  language  = {en}
}
@article{KuhlbrodtWisotzkiJahnke2001,
  author    = {Kuhlbrodt, B. and Wisotzki, Lutz and Jahnke, Knud},
  title     = {Two-dimensional modeling of AGN host galaxies},
  isbn      = {0-306-46662-7},
  year      = {2001},
  language  = {en}
}