@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 20 000) shows that the [Fe/H] estimates used for the determination of the halo MDF are accurate to within 0.3 dex, once highly C-rich stars are eliminated. We determined the selection function of the HES, which must be taken into account for a proper comparison between the HES MDF with MDFs of other stellar populations or those predicted by models of Galactic chemical evolution. The latter show a reasonable agreement with the overall shape of the HES MDF for [Fe/H] > -3.6, but only a model of Salvadori et al. (2007) with a critical metallicity for low-mass star formation of Z(cr) = 10(-3.4) Z(circle dot) reproduces the sharp drop at [Fe/H] similar to -3.6 present in the HES MDF. Although currently about ten stars at [Fe/H] < -3.6 are known, the evidence for the existence of a tail of the halo MDF extending to [Fe/H] similar to -5.5 is weak from the sample considered in this paper, because it only includes two stars [Fe/H] < -3.6. Therefore, a comparison with theoretical models has to await larger statistically complete and unbiased samples. A comparison of the MDF of Galactic globular clusters and of dSph satellites to the Galaxy shows qualitative agreement with the halo MDF, derived from the HES, once the selection function of the latter is included. However, statistical tests show that the differences between these are still highly significant.}, language = {en} } @article{ChristliebGreenWisotzkietal.2001, author = {Christlieb, N. and Green, P. J. and Wisotzki, Lutz and Reimers, Dieter}, title = {The stellar content of the Hamburg/ESO survey : II. a large, homogeneously-selected sample of high latitude carbon stars}, year = {2001}, language = {en} } @article{ChristliebWisotzkiReimersetal.2001, author = {Christlieb, N. and Wisotzki, Lutz and Reimers, Dieter and Homeier, D. and Koester, D. and Heber, Ulrich}, title = {The stellar content of the Hamburg/ESO survey : I. Automated selection of DA white dwarfs}, year = {2001}, abstract = {We describe automatic procedures for the selection of DA white dwarfs in the Hamburg/ESO objective-prism survey (HES). For this purpose, and the selection of other stellar objects (e.g., metal-poor stars and carbon stars), a flexible, robust algorithm for detection of stellar absorption and emission lines in the digital spectra of the HES was developed. Broad band (U-B, B-V) and intermediate band (Str{\"o}mgren c_1) colours can be derived directly from HES spectra, with precisions of sigma U-B=0.092 mag; sigma B-V=0.095 mag; sigma c_1=0.15 mag. We describe simulation techniques that allow one to convert model or slit spectra to HES spectra. These simulated objective-prism spectra are used to determine quantitative selection criteria, and for the study of selection functions. We present an atlas of simulated HES spectra of DA and DB white dwarfs. Our current selection algorithm is tuned to yield maximum efficiency of the candidate sample (minimum contamination with non-DAs). DA candidates are selected in the B-V versus U-B and c_1 versus W_lambda (Hbeta +Hgamma +Hdelta ) parameter spaces. The contamination of the resulting sample with hot subdwarfs is expected to be as low as ~ 8\%, while there is essentially no contamination with main sequence or horizontal branch stars. We estimate that with the present set of criteria, ~ 80\% of DAs present in the HES database are recovered. A yet higher degree of internal completeness could be reached at the expense of higher contamination. However, the external completeness is limited by additional losses caused by proper motion effects and the epoch differences between direct and spectral plates used in the HES. Based on observations collected at the European Southern Observatory, La Silla and Paranal, Chile.}, 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{ReimersWisotzki2001, author = {Reimers, Dieter and Wisotzki, Lutz}, title = {The Hamburg all sky bright QSO surveys}, isbn = {1-5838-1127-3}, year = {2001}, language = {en} } @article{Wisotzki2001, author = {Wisotzki, Lutz}, title = {The evolution of optically selected QSOs}, isbn = {1-5838-1127-3}, year = {2001}, language = {en} } @article{WolfWisotzkiBorchetal.2003, author = {Wolf, C. and Wisotzki, Lutz and Borch, Andrea and Dye, S. and Kleinheinrich, M. and Meisenheimer, Klaus}, title = {The evolution of faint AGN between z similar or equal to 1 and z similar or equal to 5 from the COMBO-17 survey}, year = {2003}, abstract = {We present a determination of the optical/UV AGN luminosity function and its evolution, based on a large sample of faint (R < 24) QSOs identified in the COMBO-17 survey. Using multi-band photometry in 17 filters within 350 nm <~ lambdaobs <~ 930 nm, we could simultaneously determine photometric redshifts with an accuracy of sigmaz <0.03 and obtain spectral energy distributions. The redshift range covered by the sample is 1.2 < z < 4.8, which implies that even at z =~ 3, the sample reaches below luminosities corresponding to MB = -23, conventionally employed to distinguish between Seyfert galaxies and quasars. We clearly detect a broad plateau-like maximum of quasar activity around z =~ 2 and map out the smooth turnover between z =~ 1 and z =~ 4. The shape of the LF is characterised by some mild curvature, but no sharp ``break'' is present within the range of luminosities covered. Using only the COMBO-17 data, the evolving LF can be adequately described by either a pure density evolution (PDE) or a pure luminosity evolution (PLE) model. However, the absence of a strong L*-like feature in the shape of the LF inhibits a robust distinction between these modes. We present a robust estimate for the integrated UV luminosity generation by AGN as a function of redshift. We find that the LF continues to rise even at the lowest luminosities probed by our survey, but that the slope is sufficiently shallow that the contribution of low-luminosity AGN to the UV luminosity density is negligible. Although our sample reaches much fainter flux levels than previous data sets, our results on space densities and LF slopes are completely consistent with extrapolations from recent major surveys such as SDSS and 2QZ.}, language = {en} } @article{WorseckProchaskaMcQuinnetal.2011, author = {Worseck, Gabor and Prochaska, J. Xavier and McQuinn, Matthew and Dall'Aglio, Aldo and Fechner, Cora and Hennawi, Joseph F. and Reimers, Dieter and Richter, Philipp and Wisotzki, Lutz}, title = {The end of Helium Reionization at z similar or equal to 2.7 Inferred from cosmic variance in HST/COS He II Ly alpha Absorption spectra}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, volume = {733}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2041-8205}, doi = {10.1088/2041-8205/733/2/L24}, pages = {6}, year = {2011}, abstract = {We report on the detection of strongly varying intergalactic He II absorption in HST/COS spectra of two z(em) similar or equal to 3 quasars. From our homogeneous analysis of the He II absorption in these and three archival sightlines, we find a marked increase in the mean He II effective optical depth from similar or equal to 1 at z similar or equal to 2.3 to greater than or similar to 5 at z similar or equal to 3.2, but with a large scatter of 2 less than or similar to tau(eff, He II) less than or similar to 5 at 2.7 < z < 3 on scales of similar to 10 proper Mpc. This scatter is primarily due to fluctuations in the He II fraction and the He II-ionizing background, rather than density variations that are probed by the coeval Hi forest. Semianalytic models of He II absorption require a strong decrease in the He II-ionizing background to explain the strong increase of the absorption at z greater than or similar to 2.7, probably indicating He II reionization was incomplete at z(reion) greater than or similar to 2.7. Likewise, recent three-dimensional numerical simulations of He II reionization qualitatively agree with the observed trend only if He II reionization completes at z(reion) similar or equal to 2.7 or even below, as suggested by a large tau(eff, He II) greater than or similar to 3 in two of our five sightlines at z < 2.8. By doubling the sample size at 2.7 less than or similar to z less than or similar to 3, our newly discovered He II sightlines for the first time probe the diversity of the second epoch of reionization when helium became fully ionized.}, language = {en} } @article{GilMerinoWisotzkiWambsganss2002, author = {Gil-Merino, Rodrigo and Wisotzki, Lutz and Wambsganß, Joachim}, title = {The Double Quasar HE 1104-1805 : a case study for time delay determination with poorly sampled lightcurves}, year = {2002}, abstract = {We present a new determination of the time delay of the gravitational lens system HE 1104-1805 (``Double Hamburger'') based on a previously unpublished dataset. We argue that the previously published value of Delta tA-B=0.73 years was affected by a bias of the employed method. We determine a new value of Delta tA-B=0.85+/-0.05 years (2sigma confidence level), using six different techniques based on non interpolation methods in the time domain. The result demonstrates that even in the case of poorly sampled lightcurves, useful information can be obtained with regard to the time delay. The error estimates were calculated through Monte Carlo simulations. With two already existing models for the lens and using its recently determined redshift, we infer a range of values of the Hubble parameter: H0=48+/-4 km s-1 Mpc-1 (2sigma ) for a singular isothermal ellipsoid (SIE) and H0=62+/-4 km s-1 Mpc-1 (2sigma ) for a constant mass-to-light ratio plus shear model (M/L+gamma ). The possibly much larger errors due to systematic uncertainties in modeling the lens potential are not included in this error estimate.}, language = {en} } @article{ChristliebWisotzkiGrasshoff2002, author = {Christlieb, N. and Wisotzki, Lutz and Graßhoff, G.}, title = {Statistical methods of automatic spectral classification and their application to the Hamburg/ESO Survey}, year = {2002}, abstract = {We employ classical statistical methods of multivariate classification for the exploitation of the stellar content of the Hamburg/ESO objective prism survey (HES). In a simulation study we investigate the precision of a three- dimensional classification (Teff, log g, [Fe/H]) achievable in the HES for stars in the effective temperature range 5200 K10 (typically corresponding to BJ<16.5). The accuracies in log g and [Fe/H] are better than 0.68 dex in the same S/N range. These precisions allow for a very efficient selection of metal-poor stars in the HES. We present a minimum cost rule for compilation of complete samples of objects of a given class, and a rejection rule for identification of corrupted or peculiar spectra. The algorithms we present are being used for the identification of other interesting objects in the HES data base as well, and they are applicable to other existing and future large data sets, such as those to be compiled by the DIVA and GAIA missions.}, 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{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{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{PaalvastVerhammeStrakaetal.2018, author = {Paalvast, M. and Verhamme, A. and Straka, L. A. and Brinchmann, J. and Herenz, Edmund Christian and Carton, D. and Gunawardhana, M. L. P. and Boogaard, L. A. and Cantalupo, S. and Contini, T. and Epinat, Benoit and Inami, H. and Marino, R. A. and Maseda, M. V. and Michel-Dansac, L. and Muzahid, S. and Nanayakkara, T. and Pezzulli, Gabriele and Richard, J. and Schaye, Joop and Segers, M. C. and Urrutia, Tanya and Wendt, Martin and Wisotzki, Lutz}, title = {Properties and redshift evolution of star-forming galaxies with high [0 III]/[O II] ratios with MUSE at 0.28 < z < 0.85}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {618}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201832866}, pages = {15}, year = {2018}, abstract = {We present a study of the [O III]/[O II] ratios of star-forming galaxies drawn from Multi-Unit Spectroscopic Explorer (MUSE) data spanning a redshift range 0.28 < z < 0.85. Recently discovered Lyman continuum (LyC) emitters have extremely high oxygen line ratios: [O III]lambda 5007/[O II]lambda lambda 3726, 3729 > 4. Here we aim to understand the properties and the occurrences of galaxies with such high line ratios. Combining data from several MUSE Guaranteed Time Observing (GTO) programmes, we select a population of star-forming galaxies with bright emission lines, from which we draw 406 galaxies for our analysis based on their position in the z-dependent star formation rate (SFR) stellar mass (M*) plane. Out of this sample 15 are identified as extreme oxygen emitters based on their [O III]/[O II] ratios (3.7\%) and 104 galaxies have [O III]/[O II] > 1 (26\%). Our analysis shows no significant correlation between M*, SFR, and the distance from the SFR M, relation with [O III]/[O II]. We find a decrease in the fraction of galaxies with [O III]/[O II] > 1 with increasing M*, however, this is most likely a result of the relationship between [O III]/[O II] and metallicity, rather than between [O III]/[O II] and M. We draw a comparison sample of local analogues with < z > 0.03 from the Sloan Digital Sky Survey, and find similar incidence rates for this sample. In order to investigate the evolution in the fraction of high [O III]/[O II] emitters with redshift, we bin the sample into three redshift subsamples of equal number, but find no evidence for a dependence on redshift. Furthermore, we compare the observed line ratios with those predicted by nebular models with no LyC escape and find that most of the extreme oxygen emitters can be reproduced by low metallicity models. The remaining galaxies are likely LyC emitter candidates.}, language = {en} } @article{BoucheFinleySchroetteretal.2016, author = {Bouche, Nicolas and Finley, H. and Schroetter, I. and Murphy, M. T. and Richter, Philipp and Bacon, Roland and Contini, Thierry and Richard, J. and Wendt, Martin and Kamann, S. and Epinat, Benoit and Cantalupo, Sebastiano and Straka, Lorrie A. and Schaye, Joop and Martin, C. L. and Peroux, C. and Wisotzki, Lutz and Soto, K. and Lilly, S. and Carollo, C. M. and Brinchmann, Jarle and Kollatschny, W.}, title = {POSSIBLE SIGNATURES OF A COLD-FLOW DISK FROM MUSE USING A z similar to 1 GALAXY-QUASAR PAIR TOWARD SDSS J1422-0001}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {820}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.3847/0004-637X/820/2/121}, pages = {1872 -- 1882}, year = {2016}, abstract = {We use a background quasar to detect the presence of circumgalactic gas around a z = 0.91 low-mass star-forming galaxy. Data from the new Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope show that the galaxy has a dust-corrected star formation rate (SFR) of 4.7 +/- 2.0. M-circle dot yr(-1), with no companion down to 0.22 M-circle dot yr(-1) (5 sigma) within 240 h(-1) kpc ("30"). Using a high-resolution spectrum of the background quasar, which is fortuitously aligned with the galaxy major axis (with an azimuth angle alpha of only 15 degrees), we find, in the gas kinematics traced by low-ionization lines, distinct signatures consistent with those expected for a "cold-flow disk" extending at least 12 kpc (3 x R-1/2). We estimate the mass accretion rate M-in to be at least two to three times larger than the SFR, using the geometric constraints from the IFU data and the H (I) column density of log N-H (I)/cm(-2) similar or equal to 20.4 obtained from a Hubble Space Telescope/COS near-UV spectrum. From a detailed analysis of the low-ionization lines (e.g., Zn II, Cr II, Ti II, MnII, Si II), the accreting material appears to be enriched to about 0.4 Z(circle dot) (albeit with large uncertainties: log Z/Z(circle dot) = -0.4 +/- 0.4), which is comparable to the galaxy metallicity (12 + log O/H = 8.7 +/- 0.2), implying a large recycling fraction from past outflows. Blueshifted Mg II and Fe II absorptions in the galaxy spectrum from the MUSE data reveal the presence of an outflow. The Mg II and Fe II absorption line ratios indicate emission infilling due to scattering processes, but the MUSE data do not show any signs of fluorescent Fe II* emission.}, language = {en} } @article{LetaweCourbinMagainetal.2004, author = {Letawe, G. and Courbin, F. and Magain, P. and Hilker, M. and Jablonka, P. and Jahnke, Knud and Wisotzki, Lutz}, title = {On-axis spectroscopy of the z=0.144 radio-loud quasar HE 1434-1600 : an elliptical host with a highly ionized ISM}, year = {2004}, abstract = {VLT on-axis optical spectroscopy of the z = 0.144 radio-loud quasar HE 1434-1600 is presented. The spatially resolved spectra of the host galaxy are deconvolved and separated from those of the central quasar in order to study the dynamics of the stars and gas as well as the physical conditions of the ISM. We find that the host of HE 1434-1600 is an elliptical galaxy that resides in a group of at least 5 member galaxies, and that most likely experienced a recent collision with its nearest companion. Compared with other quasar host galaxies, HE 1434-1600 has a highly ionized ISM. The ionization state corresponds to that of typical Seyferts, but the ionized regions are not distributed in a homogeneous way around the QSO, and are located preferentially several kiloparsecs away from it. While the stellar absorption lines do not show any significant velocity field, the gas emission lines do. The observed gas velocity field is hard to reconcile with dynamical models involving rotating disk. modified Hubble laws or power laws, that all require extreme central masses (M > 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}, 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} }