I. Appenzeller

Fe II/Mg II Emission-Line Ratio in High-Redshift Quasars*

We present results of the analysis of near infrared spectroscopic observations of 6 high-redshift quasars (z>4), emphasizing the measurement of the ultraviolet FeII/MgII emission line strength in order to estimate the beginning of intense star formation in the early universe. To investigate the evolution of the FeII/MgII ratio over a wider range in cosmic time, we measured this ratio for composite quasar spectra which cover a redshift range of 0<z<5 with nearly constant luminosity, as well as for those which span ~6 orders of magnitude in luminosity. A detailed comparison of the high-redshift quasar spectra with those of low-redshift quasars with comparable luminosity shows essentially the same FeII/MgII emission ratios and very similar continuum and line spectral properties, i.e. a lack of evolution of the relative iron to magnesium abundance of the gas in bright quasars since z=5. Current nucleosynthesis and stellar evolution models predict that alpha-elements like magnesium are produced in massive stars ending in type II SNe, while iron is formed predominantly in SNe of type Ia with intermediate mass progenitors. This results in an iron enrichment delay of 0.2 to 0.6 Gyr. We conclude that intense star formation activity in the host galaxies of z>4 quasars must have started already at an epoch corresponding to z_f = 6 to 9, when the age of the universe was ~0.5 Gyr (H_o = 72 km/s/Mpc, Omega_M = 0.3, Omega_Lambda = 0.7). This epoch corresponds well to the re-ionization era of the universe.We present results of the analysis of near-infrared spectroscopic observations of six high-redshift quasars (z 4), emphasizing the measurement of the ultraviolet Fe II/Mg II emission-line strength to estimate the beginning of intense star formation in the early universe. To investigate the evolution of the Fe II/Mg II ratio over a wider range in cosmic time, we measured this ratio for composite quasar spectra that cover a redshift range 0 z 5 with nearly constant luminosity, as well as for those that span ~6 orders of magnitude in luminosity. A detailed comparison of the high-redshift quasar spectra with those of low-redshift quasars with comparable luminosity shows essentially the same Fe II/Mg II emission ratios and very similar continuum and line spectral properties, i.e., a lack of evolution of the relative iron-to-magnesium abundance of the gas in bright quasars since z 5. Current nucleosynthesis and stellar evolution models predict that α-elements such as magnesium are produced in massive stars ending in Type II supernovae, while iron is formed predominantly in Type Ia supernovae with intermediate-mass progenitors. This results in an iron enrichment delay of ~0.2-0.6 Gyr. We conclude that intense star formation activity in the host galaxies of z 4 quasars must have started already at an epoch corresponding to zf 6-9, when the age of the universe was ~0.5 Gyr (H0 = 72 km s-1 Mpc-1, ΩM = 0.3, ΩΛ = 0.7). This epoch corresponds well to the reionization era of the universe.

Lyα emission in high-redshift galaxies ⋆

Context. A significant fraction of the high-redshift galaxies show st rong Lyα emission lines. For redshifts z> 5, most known galaxies belong to this class. However, so far not much is known about the physical structure and nature of these objects. Aims. Our aim is to analyse the Lyα emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the Lyα profile and the line strength. Methods. VLT/FORS spectra with a resolution of R≈ 2000 of 16 galaxies in the redshift range of z = 2.7 to 5 are presented. The observed Lyα profiles are compared with theoretical models. Results. The Lyα lines range from pure absorption (EW = -17 A) to strong emission (EW = 153 A). Most Lyα emission lines show an asymmetric profile, and three galaxies have a double-peaked profile. Both types of profiles can be explained by a uniform mo del consisting of an expanding shell of neutral and ionised hydrogen around a compact starburst region. The broad, blueshifted, low-ionisation interstellar absorption lines indicate a galaxy-scale outflow of the ISM. The strengths of these lines are found to be determined in part by the velocity dispersion of the outflowing medium. We find star-formation r ates of these galaxies ranging from S FRUV = 1.2 to 63.2 M⊙yr −1 uncorrected for dust absorption. Conclusions. The Lyα emission strength of our target galaxies is found to be deter mined by the amount of dust and the kinematics of the outflowing material.

DENIS: A DEEP NEAR-INFRARED SURVEY OF THE SOUTHERN SKY

The DENIS project is the first attempt to carry out a complete digitized survey of the southern sky in the range 1–2.5µm. The main objectives of the programme and the main specifications of the camera and of the data processing stream are briefly outlined

The FORS Deep Field: Field selection, photometric observations and photometric catalog ,

The FORS Deep Field project is a multi-colour, multi-object spectroscopic investigation of a ∼7 � × 7 � region near the south galactic pole based mostly on observations carried out with the FORS instruments attached to the VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this study is to improve our understanding of the formation and evolution of galaxies in the young Universe. In this paper the field selection, the photometric observations, and the data reduction are described. The source detection and photometry of objects in the FORS Deep Field is discussed in detail. A combined B and I selected UBgRIJKsphotometric catalog of 8753 objects in the FDF is presented and its properties are briefly discussed. The formal 50% completeness limits for point sources, derived from the co-added images, are 25.64, 27.69, 26.86, 26.68, 26.37, 23.60 and 21.57 in U, B, g, R, I, J and Ks(Vega-system), respectively. A comparison of the number counts in the FORS Deep Field to those derived in other deep field surveys shows very good agreement.

High-Redshift Quasars and Star Formation in the Early Universe*

In order to derive information on the star formation history in the early universe, we observed six high-redshift (z 3.4) quasars in the near-infrared to measure the relative iron and Mg II emission strengths. A detailed comparison of the resulting spectra with those of low-redshift quasars show essentially the same Fe II /Mg II emission ratios and very similar continuum and line spectral properties, indicating a lack of evolution of the relative iron to magnesium abundance of the gas since z 3.4 in bright quasars. On the basis of current chemical evolution scenarios of galaxies, where magnesium is produced in massive stars ending in Type II Supernovae (SNe II), while iron is formed predominantly in SNe Ia with a delay of ~1 Gyr and assuming as cosmological parameters H0 = 72 km s-1 Mpc-1, ?M = 0.3, and ?? = 0.7, we conclude that major star formation activity in the host galaxies of our z 3.4 quasars must have started already at an epoch corresponding to zf 10, when the age of the universe was less than 0.5 Gyr.

Identification of a Complete Sample of Northern ROSAT All-Sky Survey X-Ray Sources. III. The Catalog

We present a catalog of optical identifications of a representative sample of northern (δ > -9°) ROSAT All-Sky Survey (RASS) sources. A full identification has been carried out for a count-rate- and area-limited complete RASS subsample comprising 674 sources. All sources are within six study areas outside the Galactic plane (| b | > 196), one area being near the north Galactic pole and one near the north ecliptic pole.

The FORS Deep Field spectroscopic survey

We present a catalogue and atlas of low-resolution spectra of a well defined sample of 341 objects in the FORS Deep Field. All spectra were obtained with the FORS instruments at the ESO VLT with essentially the same spectroscopic set-up. The observed extragalactic objects cover the redshift range 0. 1t o 5.0. 98 objects are starburst galaxies and QSOs at z > 2. Using this data set we investigated the evolution of the characteristic spectral properties of bright starburst galaxies and their mutual relations as a function of redshift. Significant evolutionary effects were found for redshifts 2 < z < 4. Most conspicuous are the increase of the average C IV absorption strength, of the dust reddening, and of the intrinsic UV luminosity, and the decrease of the average Lyα emission strength with decreasing redshift. In part the observed evolutionary effects can be attributed to an increase of the metallicity of the galaxies with cosmic age. Moreover, the increase of the total star-formation rates and the stronger obscuration of the starburst cores by dusty gas clouds suggest the occurrence of more massive starbursts at later cosmic epochs.

LUCIFER : a multi-mode NIR instrument for the LBT

LUCIFER (LBT NIR-Spectroscopic Utility with Camera and Integral-Field Unit for Extragalactic Research) is a NIR spectrograph and imager for the Large Binocular Telescope (LBT) on Mt. Graham, Arizona. It is built by a consortium of five German institutes and will be one of the first light instruments for the LBT. Later, a second copy for the second mirror of the telescope will follow. Both instruments will be mounted at the bent Gregorian foci of the two individual telescope mirrors. The final design of the instrument is presently in progress. LUCIFER will work at cryogenic temperature in the wavelength range from 0.9 μm to 2.5 μm. It is equipped with three exchangeable cameras for imaging and spectroscopy: two of them are optimized for seeing-limited conditions, the third camera for the diffraction-limited case with the LBT adaptive secondary mirror working. The spectral resolution will allow for OH suppression. Up to 33 exchangeable masks will be available for longslit and multi-object spectroscopy (MOS) over the full field of view (FOV). The detector will be a Rockwell HAWAII-2 HgCdTe-array.

Edge-on T Tauri stars

Using the U echelle spectrograph at the ESO VLT we obtained two-dimensional high-resolution (R = 50 000) spectra of the edge-on disk objects HH30 ∗ , HK Tau B, and HV Tau C. For comparison purposes we also observed with the same equipment both the classical T Tauri star HL Tau and the active late-type star LDN 1551-9. The spectra of all three observed edge-on disks consist of a T Tauri emission and absorption line spectrum with superimposed jet emission lines. Analysis of the spectra confirmed that the disks are completely opaque at visible wavelengths and that light from the central objects reaches us only via scattering layers above and below the disk planes. The central objects of our targets were found to be normal T Tauri stars showing moderate but different amounts of veiling of their photospheric spectra, indicating different accretion rates or evolutionary stages. We suggest that all classical T Tauri stars (CTTSs) show this observed morphology when viewed edge-on. Part of the jet emission from edge-on systems is directly visible to us in the forbidden lines as well as in Hα and He , a finding which contradicts the present paradigm of a pure magnetospheric accretion origin for the formation of hydrogen and helium emission lines in moderately active CTTSs. From a comparison with those Taurus-Auriga CTTSs for which the inclination is reliably known, we conclude that the view angle of CTTS systems is one of the key parameters governing apparent Hα emission strength in the T Tauri class. We discuss the various possible formation regions for the Na  D lines and show that profiles similar to observed ones can be formed at the base of the disk wind.

Lyα emission galaxies at a redshift of z 5.7 in the FORS Deep Field

Context. We present the results of a search for Lyα emission galaxies at z≈ 5.7 in the FORS Deep Field. Aims. The objective of this study is to improve the faint end of the l uminosity function of high-redshift Lyα emitting galaxies and to derive properties of intrinsically faint Lyα emission galaxies in the young universe. Methods. Using FORS2 at the ESO VLT and a set of special interference fil ters, we identified candidates for high-redshift Lyα galaxies. We then used FORS2 in spectroscopic mode to verify the identific ations and to study their spectral properties. Results. The narrow-band photometry resulted in the detection of 15 likely Lyα emission galaxies. Spectra with an adequate exposure time could be obtained for eight galaxies . In all these cases the p resence of Lyα emission at z = 5.7 was confirmed spectroscopically. The line fluxes of the 15 candidates range between 3× 10 −21 Wm −2 and 16× 10 −21 Wm −2 , which corresponds to star-formation rates not corrected f or dust between 1 and 5 M⊙yr −1 . The luminosity function derived for our photometrically identified objects extends the published luminosity functio ns of intrinsically brighter Lyα galaxies. Conclusions. With this technique the study of high-redshift Lyα emission galaxies can be extended to low intrinsic luminosities.