Lutz Haberzettl

GaBoDS: The Garching-Bonn Deep Survey IV. Methods for the Image reduction of multi-chip Cameras ⋆

We present our image processing system for the reduction of optical imaging data from multi-chip cameras. In the framework of the Garching Bonn Deep Survey (GaBoDS; Schirmer et al. 2003) consisting of about 20 square degrees of high-quality data from WFI@MPG/ESO 2.2m, our group developed an imaging pipeline for the homogeneous and efficient processing of thislarge data set. Having weak gravitational lensing as the main science driver, our algorithms are optimised to produce deep co-added mosaics from individual exposures obtained from empty field observations. However, the modular design of our pipeline allows an easy adaption to different scientific applications. Our system has already been ported to a large variety of optical instruments and its products have been used in various scientific contexts. In this paper we give a thorough description of the algorithms used and a careful evaluation of the accuracies reached. This concerns the removal of the instrumental signature, the astrometric alignment, photometric calibration and the characterisation of final co-added mosaics. In addition we give a more general overview on the image reduction process and comment on observing strategies where they have significant influence on the data quality.

GaBoDS: The Garching-Bonn Deep Survey V. Data release of the ESO Deep-Public-Survey ?

Aims. In this paper the optical data of the ESO Deep-Public-Survey observed with the Wide Field Imager and reduced with the THELI pipeline are described. Methods. Here we present 63 fully reduced and stacked images. The astrometric and photometric calibrations are discussed and the properties of the images are compared to images released by the ESO Imaging Survey team covering a subset of our data. Results. These images are publicly released to the community. Our main scientific goals with this survey are to study the high-redshift universe by optically pre-selecting high-redshift objects from imaging data and to use VLT instruments for follow-up spectroscopy as well as weak lensing applications.

GaBoDS: the Garching-Bonn Deep Survey - III. Lyman-break galaxies in the Chandra Deep Field South

We present first results of our search for high-redshift galaxies in deep CCD mosaic images. As a pilot study for a larger survey, very deep images of the Chandra Deep Field South (CDFS), taken with WFI@MPG/ESO2.2m, are used to select large samples of 1070 U-band and 565 B-band dropouts with the Lyman-break method. The data of these Lyman-break galaxies are made public as an electronic table. These objects are good candidates for galaxies at z ∼ 3a ndz ∼ 4 which is supported by their photometric redshifts. The distributions of apparent magnitudes and the clustering properties of the two populations are analysed, and they show good agreement to earlier studies. We see no evolution in the comoving clustering scale length from z ∼ 3t oz ∼ 4. The techniques presented here will be applied to a much larger sample of U-dropouts from the whole survey in near future.

An optical search for low surface brightness galaxies in the Arecibo HI Strip Survey

Aims. In order to estimate the contribution of low surface brightness (LSB) galaxies to the local (z ≤ 0.1) galaxy number density, we performed an optical search for LSB candidates in a 15.5 deg 2 part of the region covered by the 65 deg 2 blind Arecibo HI Strip Survey (AHISS). Methods. Object detection and galaxy profile fitting were done with analytical algorithms. The detection efficiency and the selection effects were evaluated using large samples of artificial galaxies. Results. Our final catalogue is diameter-limited and contains 306 galaxies with diameters >18 �� at the limiting surface brightness of µB,lim = 25.2 ± 0.31 mag arcsec −2 . Of these 306 galaxies, 148 were not catalogued previously. Our results indicate that low surface brightness galaxies contribute at least to 30% to the local galaxy number density. Conclusions. Without additional distance information, choosing the limiting diameter and the surface brightness at which the diameter is measured is crucial. Depending on these choices, diameter-limited optical catalogues are either biased against LSB galaxies, or contaminated with cosmologically dimmed high surface brightness galaxies, which affects the implied surface brightness distribution. The comparison to the AHISS showed that although optical surveys detect more galaxies per deg 2 than HI surveys, their drawback is the need for spectroscopic follow up observations to derive distances. Blind HI surveys have no diameter limits, but tend to miss gaspoor galaxies and all galaxies which lie outside their redshift limits. HI and optical surveys thus provide complementary information and sample different parts of the LSB galaxy population.

The Physical Nature of Lyα-emitting Galaxies at z = 3.1*

We selected 40 candidate Lyα-emitting galaxies (LAEs) at z 3.1 with observed-frame equivalent widths greater than 150 A and inferred emission-line fluxes above 2.5 × 10-17 ergs cm-2 s-1 from deep narrowband and broadband MUSYC images of the Extended Chandra Deep Field South. Covering 992 arcmin2, this is the largest blank field surveyed for LAEs at z ~ 3, allowing an improved estimate of the space density of this population of (3 ± 1) × 10-4 h Mpc-3. Spectroscopic follow-up of 23 candidates yielded 18 redshifts, all at z 3.1. Over 80% of the LAEs are dimmer in continuum magnitude than the typical Lyman break galaxy (LBG) spectroscopic limit of R = 25.5 (AB), with a median continuum magnitude R 27 and very blue continuum colors, V-z 0. Over 80% of the LAEs have the right UVR colors to be selected as LBGs, but only 10% also have R ≤ 25.5. Stacking the UBVRIzJK fluxes reveals that LAEs have stellar masses 5 × 108 h M☉ and minimal dust extinction, AV 0.1. Inferred star formation rates are 6 h M☉ yr-1, yielding a cosmic star formation rate density of 2 × 10-3 h70 M☉ yr-1 Mpc-3. None of our LAE candidates show evidence for rest-frame emission-line equivalent widths EWrest > 240 A that might imply a nonstandard initial mass function. One candidate is detected by Chandra, implying an AGN fraction of 2% ± 2% for LAE candidate samples. In summary, LAEs at z ~ 3 have rapid star formation, low stellar mass, little dust obscuration, and no evidence for a substantial AGN component.

Low Surface Brightness Galaxies Around the Hubble Deep Field South

We present results from a study of the SFH of a sample of LSB galaxies around the HDF-S. For the selection of the LSB galaxy candidates we used color–color diagrams, from which we selected the candidates based on their different location in comparison to the HSB galaxy redshift tracks. We compared measured spectra to synthetic SEDs from synthesis evolution models. We were able to fit SEDs in the range of 2 to 5 Gyr to the spectra of the LSB galaxies, while applying the same method to a sample of HSB galaxies resulted in an averaged stellar population of about 10 to 14 Gyr. Therefore, LSB galaxies tend to show much younger averaged stellar populations. This implies that the major star formation event of LSB galaxies took place at a redshift of z ∼ 0.2 to 0.4 while for HSB galaxies this tends to be at z ∼ 2 to 4.

A Multi Wavelength Study of Moderate Luminosity Mergers

Interaction and merging are the two most important driving forces of galaxy evolution. In recent years, much research activity has been focused on ULIRGs, which are the result of a disk‐disk merger, since they are among the most spectacular objects in the universe. However, ULIRGs are rare objects in the local universe. Thus, a study of a sample of merging galaxies of moderate FIR luminosity (∼ 1010 – 1011L⊙) may teach us as much as or even more about galaxy formation and evolution as investigations of the most extreme objects. Mergers having a moderate FIR luminosity can also be produced by merging two gas‐rich galaxies with unequal mass or a spiral and an elliptical (S+E). Alternatively, they can be a result of a faded major merger. As a class, moderate luminosity mergers are poorly studied and their role in the overall process of galaxy evolution is not yet well understood. We have obtained multicolour optical and NIR imaging data, optical spectroscopy, HI and CO (i.e. molecular gas) data for a large p...

Star Formation History of a Sample of LSB Galaxies in the HDF‐S

We present results from a study of the star formation history (SFH) of a sample of Low Surface Brightness (LSB) galaxies. The LSB sample resulted from a search around the HDF‐S (field size: 0.6 deg2) using SExtractor in combination with a median filter technique. For the selection of the LSB galaxy candidates we used color‐color diagrams (U‐B vs. B‐R). From the color‐color diagram LSB candidates were selected based on their different location in comparison to the High Surface Brightness (HSB) galaxy redshift tracks. With this method and a lower diameter limit of 10 arcsec we derived a sample of 7 LSB galaxies. For this sample we derived spectral energy distributions (SEDs) from 3500 A to 7000 A using ESO 3.6m telescope. The measured SEDs we compared to synthetic spectra extracted from the synthesis evolution model PEGASE (Rocca & Volmerange 1997). The synthetic spectra were derived assuming exponential declining SFR using decay times between 500 Myr and 5 Gyr. Comparing a library of nearly 3000 sunthetic ...

Lyman break galaxies at z∼3 and z∼4 in the Chandra Deep Field South

We present first results of a Lyman break galaxy survey in the complete 30′ by 30′ Chandra Deep Field South (CDFS) based on deep, multi‐color CCD mosaic images. We find more than 1100 U‐band and 600 B‐band drop‐outs, consistent with the expectations from earlier searches in smaller fields. The results of the 2‐point correlation functions agree well with earlier results on smaller fields, too. Due to the full coverage of the survey field with HST‐ACS images, we can study the structure of the Lyman break galaxies, which turn out to span a large range in morphologies.