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GOODS/FORS2 Data Release: Version 2.0

24 December 2005

Overview and field layout	Acknowledgements
Release Content	Interactive search engine
Notes on v2.0 Data Release	Request all data
Data format	Request data tables

As part of the Great Observatories Origins Deep Survey (GOODS), multi-object, optical to NIR spectroscopy in the Chandra Deep Field South (CDF-S) has been carried out, using the FORS2 instrument mounted at the Kueyen Unit Telescope of the VLT at ESO's Cerro Paranal Observatory, Chile.

This release contains the results of the ESO/GOODS large program LP170.A-0788 (PI Cesarsky) of spectroscopy of faint galaxies in the Chandra Deep Field South (CDF-S). 1204 spectra of 930 unique targets have been obtained in service mode with the FORS2 spectrograph during the period September 2002 - February 2004, providing in total 943 redshift measurements with quality flag A, B or C (A=solid redshift, B=likely redshift, C=potential redshift). 725 of the unique targets have an assigned redshift with quality flag A, B or C. The average of the redshift distribution is z=1.5 (median z=1.1). The typical redshift uncertainty is estimated to be +/-0.005.

In this release we provide the full set of extracted 1-dimensional fits spectra in the GOODS/FORS2 survey (LP170.A-0788) and associated spectral previews and colour image cutouts (5"x5") for each target. Furthermore, a catalogue is provided where we give for each target the basic ACS image information such as magnitude (in the AB system) and colours as well as the measured redshift and associated comments.

A full description of the survey can be found in the accompanying papers "The Great Observatories Origins Deep Survey - VLT/FORS2 Spectroscopy in the GOODS-South Field", 2005, A&A, 434, 53 (description of the first spectroscopic campaign) and "The Great Observatories Origins Deep Survey - VLT/FORS2 Spectroscopy in the GOODS-South Field - Part II", 2006, A&A, accepted; astro-ph/0601367 (presentation of the whole dataset).

The data were reduced and prepared for release by a collaboration of the GOODS Team, ESO (Advanced Data Products group in the Virtual Observatory Systems department) and ST-ECF staff.

Overview and field layout

All observed FORS2 targets in this release are overlayed on the HST/ACS GOODS z-band mosaic. Blue open circles stand for targets with a redshift in quality A,B,C and black open circles indicate observed targets without a redshift identification. [Click to get full size image]

In order to have a sufficient surface density of targets and fully exploit the red sensitivity of FORS2, spectroscopic targets have been selected according to the following criteria (all magnitudes are in the AB system in the ACS/GOODS filter set):

Primary catalog:          (i-z)>0.6,  z<25.0
Secondary catalog:   0.45<(i-z)<0.6,  z<25.0

Content of this release

Summary of reduced FORS2 observations

In total 27 different multi-object masks were created and observed for the GOODS/FORS2 survey. A table listing the Mask IDs, the associated fims files, OB names and FORS2 pre-images can be seen here.   A total of 1204 spectra could be extracted from the FORS2 observations and are presented in this release. For 70 objects we combined spectra from different masks to provide a higher signal-to-noise spectrum - the so called "stacked" spectra. These spectra are provided in addition to the normal 1-dimensional fits files. Throuhgout the FORS2 survey, 1" wide slits have been used with a wavelength range of approximately 6000 to 10000 Å sampled at roughly 3.2 Å/pixel.

The ACS catalog was used for slit-mask design and ACS imaging was used to design slit-masks after registration with FORS2 preimaging. The updated ACS catalogue (v1.1) can be downloaded from STScI GOODS page.

Comparison to previous releases
This release is the second of this survey and superseeds the previous ESO/GOODS data release. It revises and significantly extends the previous v1.0 release of June 25, 2004. The first release consisted of only 9 FORS2 masks, while the current release features the entire dataset of LP170.A-0788 consisting of 27 MXU masks.

The interactive search engine
In order to allow the user community to easily browse and utilize the contents of this release we provide an interactive search engine with an interface similar to the ST-ECF/ESO archive. While one can simply search by whole or partial object name, the real strength of the archive is the ability to select sub-samples matching specific coordinates, redshifts, magnitudes, or colours. It is also possible to limit the search by specifics of the instrumental setup like FORS2/MXU Mask ID or slit geometry.

Click here for interactive search engine

Notes on v2.0 Data Release

Data reduction method

Flux calibration

Known caveats in this release

Note, that the flux units given in the FITS headers of 1-dim spectra (keyword BUNIT = erg/sec/cm²/Å) are missing the scaling factor of 0.69x10^-16.

Updates and changes to the scientific content of this release which became only known to us after the package was build are logged in the following file: FORS2_DR2.0_change_log.txt, where changes/comments on individual targets from the user community will be recorded.

The spectral previews show only a restricted wavelength range. For access to the full wavelength range we refer to the fits spectra.

A small number of the colour image previews do not cover the full 5"x5" FOV. This problem occurs when a target is located close to the edges of the image tiles which do not overlap.

Objects identified as stars by the stellar class parameter or the spectrum itself were asigned a fixed redshift of 0.000.

The observations from the first two masks in the survey (Mask ID: 994852 and 995131) were reduced in a somewhat different manner than the rest of the survey. Specifically, the spectra of targets in common were combined right away and the individual spectra are not available.

Data format

The following file naming convention has been adopted for all individual extracted spectra:

for the target coordinate <xx> as derived from the ACS 5-epoch stack (e.g., J033206.44-274728.8); <bb> indicates the mask ID of the observation (e.g., 961839). Here is an example of a full, valid name: GOODS_FORS2_GDS_J033206.44-274728.8_985831_v2.0.fits
For stacked spectra, which are combinations of observations from different masks we omit the mask ID:

The released datatables, containing object-id, photometry and redshift information, are available in Ascii, DS9 catalog (version 4), FITS-table, and VOTable format.

Plese send all comments and inquiries to <goods@eso.org>

Acknowledgements

Observations have been carried out using the Very Large Telescope at the ESO Paranal Observatory under Program ID: LP170.A-0788.

Send comments to <goods@eso.org>  Last modified: Tue Apr 18 11:27:29 CEST 2006