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<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
Y1  - 2004
SN  - 0004-637X
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<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
Y1  - 2004
SN  - 0004-637X
ER  -