@article{ChristensenSchulteLadbeckSanchezetal.2005,
  author    = {Christensen, Lise Bech and Schulte-Ladbeck, R. E. and Sanchez, Sebastian F. and Becker, Thomas and Jahnke, Knud and Kelz, A. and Roth, Martin M. and Wisotzki, Lutz},
  title     = {Abundances and kinematics of a candidate sub-damped Lymana galaxy toward PHL 1226},
  year      = {2005},
  abstract  = {The spectrum of the quasar PHL 1226 is known to have a strong Mg II and sub-damped Lymanalpha (sub-DLA) absorption line system with N(H I) = (5 +/- 2) x 10(19) cm(-2) at z = 0.1602. Using integral field spectra from the Potsdam Multi Aperture Spectrophotometer (PMAS) we investigate a galaxy at an impact parameter of 6".4 which is most probably responsible for the absorption lines. A fainter galaxy at a similar redshift and a slightly larger distance from the QSO is known to exist, but we assume that the absorption is caused by the more nearby galaxy. From optical Balmer lines we estimate an intrinsic reddening consistent with 0, and a moderate star formation rate of 0.5 M-circle dot yr(-1) is inferred from the Ha luminosity. Using nebular emission line ratios we find a solar oxygen abundance 12 + log (O/H) = 8.7 +/- 0.1 and a solar nitrogen to oxygen abundance ratio log (N/O) = -1.0 +/- 0.2. This abundance is larger than those of all known sub-DLA systems derived from analyses of metal absorption lines in quasar spectra. On the other hand, the properties are compatible with the most metal rich galaxies responsible for strong Mg II absorption systems. These two categories can be reconciled if we assume an abundance gradient similar to local galaxies. Under that assumption we predict abundances 12 + log (O/H) = 7.1 and log (N/O) = -1.9 for the sub-DLA cloud, which is similar to high redshift DLA and sub-DLA systems. We find evidence for a rotational velocity of similar to200 km s(-1) over a length of similar to7 kpc. From the geometry and kinematics of the galaxy we estimate that the absorbing cloud does not belong to a rotating disk, but could originate in a rotating halo},
  language  = {en}
}
@article{SanchezJahnkeWisotzkietal.2004,
  author    = {Sanchez, Sebastian F. and Jahnke, Knud and Wisotzki, Lutz and McIntosh, Daniel H. and Bell, Eric F. and Barden, Marko and Beckwith, Steven V. W. and Borch, Andrea and Caldwell, John A. R. and Haussler, Boris and Jogee, Shardha and Meisenheimer, Klaus and Peng, Chen Y. and Rix, Hans-Walter and Somerville, Rachel S. and Wolf, C.},
  title     = {Colors of active galactic nucleus host galaxies at 0.5 < z < 1.1 from the GEMS survey},
  issn      = {0004-637X},
  year      = {2004},
  abstract  = {We present the results from a study of the host galaxies of 15 optically selected active galactic nuclei (AGNs) with 0.5<z<1.1 from the Galaxy Evolution from Morphology and SEDs project (GEMS). GEMS is a Hubble Space Telescope imaging survey of a similar to28' x 28' contiguous field centered on the Chandra Deep Field-South in the F606W and F850LP filter bands. It incorporates the spectral energy distributions and redshifts of similar to10,000 objects, obtained by the COMBO-17 project. We have detected the host galaxies of all 15 AGNs in the F850LP band (and 13 of 15 in the F606W band), recovering their fluxes, morphologies, and structural parameters. We find that 80\% of the host galaxies have early-type (bulge-dominated) morphologies, while the rest have structures characteristic of late-type (disk-dominated) galaxies. We find that 25\% of the early types and 30\% of the late types exhibit disturbances consistent with galaxy interactions. The hosts show a wide range of colors, from those of red-sequence galaxies to blue colors consistent with ongoing star formation. Roughly 70\% of the morphologically early-type hosts have rest-frame blue colors, a much larger fraction than those typical of nonactive morphologically early-type galaxies in this redshift and luminosity range. Yet, we find that the early-type hosts are structurally similar to red-sequence elliptical galaxies, inasmuch as they follow an absolute magnitude versus half-light size correlation that is consistent with the mean relation for early-type galaxies at similar redshifts},
  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{BardenRixSomervilleetal.2005,
  author    = {Barden, Marco and Rix, Hans-Walter and Somerville, Rachel S. and Bell, Eric F. and H{\"a}ußler, Boris and Peng, Chen Y. and Borch, Andrea and Beckwith, Steven V. W. and Caldwell, John A. R. and Heymans, Catherine and Jahnke, Knud and Jogee, Shardha and McIntosh, Daniel H. and Meisenheimer, Klaus and Sanchez, Sebastian F. and Wisotzki, Lutz and Wolf, C.},
  title     = {GEMS : the surface brightness and surface mass density evolution of disk galaxies},
  year      = {2005},
  abstract  = {We combine HST imaging from the GEMS ( Galaxy Evolution from Morphologies and SEDs) survey with photometric redshifts from COMBO-17 to explore the evolution of disk-dominated galaxies since z less than or similar to 1.1. The sample is composed of all GEMS galaxies with Sersic indices n < 2.5, derived from fits to the galaxy images. We account fully for selection effects through careful analysis of image simulations; we are limited by the depth of the redshift and HST data to the study of galaxies with M-V less than or similar to -20, or equivalently, log (M/M-circle dot) greater than or similar to 10. We find strong evolution in the magnitude-size scaling relation for galaxies with M-V less than or similar to -20, corresponding to a brightening of similar to 1 mag arcsec(-2) in rest-frame V band by z similar to 1. Yet disks at a given absolute magnitude are bluer and have lower stellar mass-to-light ratios at z similar to 1 than at the present day. As a result, our findings indicate weak or no evolution in the relation between stellar mass and effective disk size for galaxies with log (M/M-circle dot) greater than or similar to 10 over the same time interval. This is strongly inconsistent with the most naive theoretical expectation, in which disk size scales in proportion to the halo virial radius, which would predict that disks are a factor of 2 denser at fixed mass at z similar to 1. The lack of evolution in the stellar mass-size relation is consistent with an "inside-out'' growth of galaxy disks on average (galaxies increasing in size as they grow more massive), although we cannot rule out more complex evolutionary scenarios},
  language  = {en}
}
@article{WisotzkiSchechterChenetal.2004,
  author    = {Wisotzki, Lutz and Schechter, P. L. and Chen, H. W. and Richstone, D. and Jahnke, Knud and Sanchez, Sebastian F. and Reimers, Dieter},
  title     = {HE 0047-1756 : a new gravitationally lensed double QSO},
  issn      = {0004-6361},
  year      = {2004},
  abstract  = {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},
  language  = {en}
}
@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{ChristensenSanchezJahnkeetal.2004,
  author    = {Christensen, Lise Bech and Sanchez, Sebastian F. and Jahnke, Knud and Becker, Thomas and Kelz, A. and Wisotzki, Lutz and Roth, Martin M.},
  title     = {Integral field observations of damped Lyman-alpha galaxies},
  year      = {2004},
  abstract  = {We report preliminary results from a targeted investigation on quasars containing damped Lyman-alpha absorption (DLA) lines as well strong metal absorption lines, carried out with the Potsdam Multi Aperture Spectrophotometer (PMAS). We search for line-emitting objects at the same redshift as the absorption lines and close to the line of sight of the QSOs. We have observed and detected the already confirmed absorbing galaxies in Q2233+131 (Z(abs) = 3.15) and Q0151+045 (Z(abs),= 0.168), while failing to find spectral signatures for the z = 0.091 absorber in Q0738+313. From the Q2233+131 DLA galaxy, we have detected extended Lyalpha emission from an area of 3" x 5"},
  language  = {en}
}
@article{WisotzkiBeckerChristensenetal.2004,
  author    = {Wisotzki, Lutz and Becker, Thomas and Christensen, Lise Bech and Jahnke, Knud and Helms, Andreas and Kelz, A. and Roth, Martin M. and Sanchez, Sebastian F.},
  title     = {Integral field spectrophotometry of gravitationally lensed QSOs with PMAS},
  issn      = {0004-6337},
  year      = {2004},
  abstract  = {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},
  language  = {en}
}
@article{ChristensenSanchezJahnkeetal.2004,
  author    = {Christensen, Lise Bech and Sanchez, Sebastian F. and Jahnke, Knud and Becker, Thomas and Wisotzki, Lutz and Kelz, A. and Popovic, L. C. and Roth, Martin M.},
  title     = {Integral field spectroscopy of extended Ly alpha emission from the DLA galaxy in Q2233+131},
  year      = {2004},
  abstract  = {This paper presents observations of an extended Lyman-alpha emission nebula surrounding the galaxy responsible for the Damped Lyman-alpha Absorption (DLA) line in the spectrum of the quasar Q2233+131. With the Potsdam Multi Aperture Spectrophotometer (PMAS) we measure the properties of the extended Lyalpha emission in an area of 3" x 5" having a total line flux of (2.8 +/- 0.3) x 10(-16) erg cm(-2) s(-1), which at redshift z = 3.15 corresponds to a luminosity of (2.4(-0.2)(+0.3)) x 10(43) erg s(-1) and a size of 23 x 38 kpc. The location of the emission is spatially coincident with the previously detected DLA galaxy, but extends significantly beyond its limb. We argue that the Lya emission is likely to be caused by an outflow from the DLA galaxy, presumably powered by star formation. In the case of negligible dust extinction, the Lya luminosity indicates a star-formation rate of 19 +/- 10 M-. yr(-1) consistent with that derived from the UV continuum flux from the parent galaxy. The wind velocity indicated by the integral field spectra is of the order of several hundred km s(-1). We find no indication of emission originating in a rotating disk},
  language  = {en}
}
@article{JahnkeWisotzkiSanchezetal.2004,
  author    = {Jahnke, Knud and Wisotzki, Lutz and Sanchez, Sebastian F. and Christensen, Lise Bech and Becker, Thomas and Kelz, A. and Roth, Martin M.},
  title     = {Integral field spectroscopy of QSO host galaxies},
  year      = {2004},
  abstract  = {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},
  language  = {en}
}
@article{ChristensenBeckerJahnkeetal.2003,
  author    = {Christensen, Lise Bech and Becker, Thomas and Jahnke, Knud and Kelz, A. and Roth, Martin M. and Sanchez, S. S. and Wisotzki, Lutz},
  title     = {Integral field spectroscopy of SN 2002er with PMAS},
  year      = {2003},
  abstract  = {sent observations of the Type Ia supernova SN 2002er during the brightening phase. The observations were performed with the Potsdam Multi Aperture Spectrophotometer (PMAS) integral field instrument. Due to the 8arcsecx8 arcsec field of view of the spectrograph an accurate background subtraction was possible. Results from analyses of the evolution of absorption features in comparisons with other SNe show that SN 2002er is a fairly bright Type Ia supernova with a peak brightness of MB=-19.6+/-0.1.},
  language  = {en}
}
@article{WisotzkiBeckerChristensenetal.2003,
  author    = {Wisotzki, Lutz and Becker, Thomas and Christensen, Lise Bech and Helms, Andreas and Jahnke, Knud and Kelz, A. and Roth, Martin M. and Sanchez, Sebastian F.},
  title     = {Integral-field spectrophotometry of the quadruple QSO HE 0435-1223 : Evidence for microlensing},
  year      = {2003},
  abstract  = {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.},
  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{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{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{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{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{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}
}
@article{JahnkeSanchezWisotzkietal.2004,
  author    = {Jahnke, Knud and Sanchez, Sebastian F. and Wisotzki, Lutz and Barden, Marco and Beckwith, Steven V. W. and Bell, Eric F. and Borch, Andrea and Caldwell, John A. R. and H{\"a}ußler, Boris and Heymans, Catherine and Jogee, Shardha and McIntosh, Daniel H. and Meisenheimer, Klaus and Peng, Chen Y. and Rix, Hans-Walter and Somerville, Rachel S. and Wolf, C.},
  title     = {Ultraviolet light from young stars in GEMS quasar host galaxies at 1.8 < z < 2.75},
  issn      = {0004-637X},
  year      = {2004},
  abstract  = {We have performed Hubble Space Telescope imaging of a sample of 23 high-redshift (1.8<z<2.75) active galactic nuclei (AGNs), drawn from the COMBO-17 survey. The sample contains moderately luminous quasars (M(B)similar to-23). The data are part of the Galaxy Evolution from Morphologies and SEDs imaging survey that provides high-resolution optical images obtained with the Advanced Camera for Surveys in two bands (F606W and F850LP), sampling the rest-frame UV flux of the targets. To deblend the AGN images into nuclear and resolved (host galaxy) components, we use a point-spread function subtraction technique that is strictly conservative with respect to the flux of the host galaxy. We resolve the host galaxies in both filter bands in nine of the 23 AGNs, whereas the remaining 14 objects are considered nondetections, with upper limits of less than 5\% of the nuclear flux. However, when we co-add the unresolved AGN images into a single high signal-to-noise ratio composite image, we find again an unambiguously resolved host galaxy. The recovered host galaxies have apparent magnitudes of 23.0<F606W<26.0 and 22.5<F850LP<24.5, with rest-frame UV colors in the range -0.2<(F606W-F850LP)(obs)<2.3. The rest-frame absolute magnitudes at 200 nm are -20.0<M-200 nm<-22.2. The photometric properties of the composite host are consistent with the individual resolved host galaxies. We find that the UV colors of all host galaxies are substantially bluer than expected from an old population of stars with formation redshift z<=5, independent of the assumed metallicities. These UV colors and luminosities range up to the values found for Lyman break galaxies (LBGs) at z=3. Our results suggest either a recent starburst of, e. g., a few percent of the total stellar mass at 100 Myr before observation, with mass fraction and age strongly degenerate, or the possibility that the detected UV emission may be due to young stars forming continuously. For the latter case we estimate star formation rates of typically \&SIM;6 M\&ODOT; yr(-1) (uncorrected for internal dust attenuation), which again lies in the range of rates implied from the UV flux of LBGs. Our results agree with the recent discovery of enhanced blue stellar light in AGN hosts at lower redshifts},
  language  = {en}
}