TY - JOUR A1 - Wisotzki, Lutz A1 - Schechter, P. L. A1 - Chen, H. W. A1 - Richstone, D. A1 - Jahnke, Knud A1 - Sanchez, Sebastian F. A1 - Reimers, Dieter T1 - HE 0047-1756 : a new gravitationally lensed double QSO N2 - The quasar HE 0047-1756, at z = 1.67, is found to be split into two images 1."144 apart by an intervening galaxy acting as a gravitational lens. The flux ratio for the two components is roughly 3.5:1, depending slightly upon wavelength. The lensing galaxy is seen on images obtained in the i (800 nm) and K-s bands (2.1 mum); there is also a nearby faint object which may be responsible for some shear. The spectra of the two quasar images are nearly identical, but the emission line ratio between the two components scale differently from the continuum. Moreover, the fainter component has a bluer continuum slope than the brighter one. We argue that these small differences are probably due to microlensing. There is evidence for a partial Einstein ring emanating from the brighter image toward the fainter one Y1 - 2004 SN - 0004-6361 ER - TY - JOUR A1 - Wisotzki, Lutz A1 - Kuhlbrodt, B. A1 - Jahnke, Knud T1 - The luminosity function of QSO host galaxies Y1 - 2001 SN - 0-306-46662-7 ER - TY - JOUR A1 - Wisotzki, Lutz A1 - Becker, Thomas A1 - Christensen, Lise Bech A1 - Jahnke, Knud A1 - Helms, Andreas A1 - Kelz, A. A1 - Roth, Martin M. A1 - Sanchez, Sebastian F. T1 - Integral field spectrophotometry of gravitationally lensed QSOs with PMAS N2 - We present spatially resolved spectrophotometric observations of multiply imaged QSOs, using the Potsdam Multi- Aperture Spectrophotometer (PMAS), with the intention to search for spectral differences between components indicative of either microlensing or dust extinction. For the quadruple QSO HE 0435-1223 we find that the continuum shapes are indistinguishable, therefore differential extinction is negligible. The equivalent widths of the broad emission lines are however significantly different, and we argue that this is most likely due to microlensing. Contrariwise, the two components of the well-known object UM 673 have virtually identical emission line properties, but the continuum slopes differ significantly and indicate different dust extinction along both lines of sight Y1 - 2004 SN - 0004-6337 ER - TY - JOUR A1 - Wisotzki, Lutz A1 - Becker, Thomas A1 - Christensen, Lise Bech A1 - Helms, Andreas A1 - Jahnke, Knud A1 - Kelz, A. A1 - Roth, Martin M. A1 - Sanchez, Sebastian F. T1 - Integral-field spectrophotometry of the quadruple QSO HE 0435-1223 : Evidence for microlensing N2 - We present the first spatially resolved spectroscopic observations of the recently discovered quadruple QSO and gravitational lens HE 0435-1223. Using the Potsdam Multi-Aperture Spectrophotometer (PMAS), we show that all four QSO components have very similar but not identical spectra. In particular, the spectral slopes of components A, B, and D are indistinguishable, implying that extinction due to dust plays no major role in the lensing galaxy. While also the emission line profiles are identical within the error bars, as expected from lensing, the equivalent widths show significant differences between components. Most likely, microlensing is responsible for this phenomenon. This is also consistent with the fact that component D, which shows the highest relative continuum level, has brightened by 0.07 mag since Dec. 2001. We find that the emission line flux ratios between the components are in better agreement with simple lens models than broad band or continuum measurements, but that the discrepancies between model and data are still unacceptably large. Finally, we present a detection of the lensing galaxy, although this is close to the limits of the data. Comparing with a model galaxy spectrum, we obtain a redshift estimate of zlens=0.44+/- 0.02. Y1 - 2003 ER - TY - JOUR A1 - Sanchez, Sebastian F. A1 - Jahnke, Knud A1 - Wisotzki, Lutz A1 - McIntosh, Daniel H. A1 - Bell, Eric F. A1 - Barden, Marko A1 - Beckwith, Steven V. W. A1 - Borch, Andrea A1 - Caldwell, John A. R. A1 - Haussler, Boris A1 - Jogee, Shardha A1 - Meisenheimer, Klaus A1 - Peng, Chen Y. A1 - Rix, Hans-Walter A1 - Somerville, Rachel S. A1 - Wolf, C. T1 - Colors of active galactic nucleus host galaxies at 0.5 < z < 1.1 from the GEMS survey N2 - We present the results from a study of the host galaxies of 15 optically selected active galactic nuclei (AGNs) with 0.5 10(9) M-circle dot) to provide only poor fit to the data. Power law models, which best fit the data, provide a total mass of M(<10 kpc) = 9.2 x 10(10) M-&ODOT;. We conclude that the recent interaction between HE 1434-1600 and its closest companion has strongly affected the gas velocity and ionization state, from the center of the galaxy to its most external parts Y1 - 2004 ER - TY - JOUR A1 - Kuhlbrodt, B. A1 - Wisotzki, Lutz A1 - Jahnke, Knud T1 - Decomposition of active galactic nucleus host galaxy images N2 - 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 Y1 - 2004 SN - 0035-8711 ER - TY - JOUR A1 - Kuhlbrodt, B. A1 - Wisotzki, Lutz A1 - Jahnke, Knud T1 - Two-dimensional modeling of AGN host galaxies Y1 - 2001 SN - 0-306-46662-7 ER - TY - JOUR A1 - Kuhlbrodt, B. A1 - Orndahl, E. A1 - Wisotzki, Lutz A1 - Jahnke, Knud T1 - High-redshift quasar host galaxies with adaptive optics N2 - 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 Y1 - 2005 SN - 0004-6361 ER - TY - JOUR A1 - Jahnke, Knud A1 - Wisotzki, Lutz A1 - Sanchez, Sebastian F. A1 - Christensen, Lise Bech A1 - Becker, Thomas A1 - Kelz, A. A1 - Roth, Martin M. T1 - Integral field spectroscopy of QSO host galaxies N2 - We describe a project to study the state of the ISM in similar to20 low redshift (z < 0.3) QSO host galaxies observed with the PMAS integral field spectrograph. We describe the development of the method to access the stellar and gas components of the spectrum without the strong nuclear emission, in order to access the host galaxy properties in the central region. It shows that integral field spectroscopy promises to be very efficient in studying the gas distribution and its velocity field, and also the spatially resolved stellar population in the host galaxies of luminous AGN Y1 - 2004 ER - TY - JOUR A1 - Jahnke, Knud A1 - Sanchez, Sebastian F. A1 - Wisotzki, Lutz A1 - Barden, Marco A1 - Beckwith, Steven V. W. A1 - Bell, Eric F. A1 - Borch, Andrea A1 - Caldwell, John A. R. A1 - Häußler, Boris A1 - Heymans, Catherine A1 - Jogee, Shardha A1 - McIntosh, Daniel H. A1 - Meisenheimer, Klaus A1 - Peng, Chen Y. A1 - Rix, Hans-Walter A1 - Somerville, Rachel S. A1 - Wolf, C. T1 - Ultraviolet light from young stars in GEMS quasar host galaxies at 1.8 < z < 2.75 N2 - We have performed Hubble Space Telescope imaging of a sample of 23 high-redshift (1.8