@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}
}
@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}
}