30 October 2007

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 final, cumulative data release of spectroscopy of faint galaxies in the Chandra Deep Field South (CDF-S), resulting from the ESO/GOODS large program under program IDs 170.A-0788, 074.A-0709, and 275.A-5060 (PI Cesarsky), supersedes all previous releases. This release accumulates 1715 spectra of 1225 unique targets which have been obtained with the FORS2 spectrograph between September 2002 and October 2006, providing in total 1165 redshift measurements, thereof being 663, 309, and 193 redshifts with quality flag A (solid redshift), B (likely redshift), and C (potential redshift), respectively. 868 of the unique targets have an assigned redshift (z>0) with quality flag A, B or C. The average of the redshift distribution (z>0) is z=1.666 (median z=1.158). The typical error in the redshift determination (of course it depends on the S/N of the spectrum) is in general +/-0.001 as we calculated in the papaer II (A&A 454, 423-435 (2006)) by comparing the redshift of sources in common with other spectroscopic survey. New in this release are 441 spectra which have been obtained between October 2005 and October 2006 using 12 different MXU masks, thus significantly extending the redshift sample by 194 unique targets with respect to the previous release (v2.0).

In this release we provide the full set of extracted 1-dimensional fits spectra in the GOODS/FORS2 survey 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), "The Great Observatories Origins Deep Survey - VLT/FORS2 Spectroscopy in the GOODS-South Field - Part II", 2006, A&A, 454, 423 (results of the second campaign), and "The Great Observatories Origins Deep Survey - VLT/FORS2 Spectroscopy in the GOODS-South Field: Part III", 2007, A&A, accepted (presentation of the full data set, see the full resolution PDF here).

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
• Release content
• Release notes
• Data format
• Data retrieval
• Acknowledgements
• Interactive search engine

Overview and field layout

Spatial distribution in the GOODS-S field of the FORS2 spectroscopic catalog (887 redshift determinations). 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 color selection criteria (all magnitudes are in the AB system in the ACS/GOODS filter set):
Primary catalog: (i-z)>0.6, z<26
Secondary catalog: 0.45<(i-z)<0.6, z<26

and

1.0 < z_phot < 2.0.

When designing slit-masks, higher priority was assigned to brighter objects (in z-band). An additional catalog of "fillers" was constructed using objects with photometric redshift in the range 1.0<z<2 (not already included in the main catalogs), and a number of interesting B_435, V_606 and i_775 dropouts (with no z_mag limit). Please refer to the publication Vanzella et al. 2007, A&A, accepted for the complete description of the target selection procedure.

Release content

Summary of reduced FORS2 observations

A table listing the Mask IDs, the associated fims files, OB names and FORS2 pre-images can be seen here. A total of 1715 spectra could be extracted from the FORS2 observations and are presented in this release. For 81 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 which is the third and final of this survey supersedes the previous ESO/GOODS FORS2 data releases. It revises and significantly extends the previous v2.0 release of December 2005 which consisted of 27 masks.

In the previous release a flux scaling factor of 0.69x10^-16 had to be applied to the data in order to obtain the flux in physical units as specified in BUNIT (erg/sec/cm²/Å). Note that the factor of 0.69 has already been applied to the data for all spectra of this release, i.e. the physical unit of the flux is now completely specified by BUNIT (10^-16 erg/sec/cm²/Å).

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 the interactive search engine

Release Notes

Data reduction method

The FORS2 observations were reduced with a semi-automatic pipeline in the MIDAS package. Redshifts were measured with the IRAF package rvsao. Details of the data reduction and analysis are fully described in the papers "The Great Observatories Origins Deep Survey - VLT/FORS2 Spectroscopy in the GOODS-South Field", 2005, A&A, 434, 53 and "The Great Observatories Origins Deep Survey - VLT/FORS2 Spectroscopy in the GOODS-South Field - Part II", 2006, A&A, 454, 423.

Flux calibration

The physical flux unit of the 1-dim spectra is specified by the FITS keyword BUNIT. However, the flux calibration should be considred as approximate since most observations were not taken in photometric conditions. Furthermore, the response curve is based on standard star observations from a different observing program and throughout the FORS2 survey an observing setup omitting the order sorting filter was used. Particularly redwards of approx. 9000 Å, the spectral response function is problematic.

Known caveats in this release

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_DR3.0_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.

Data format

The data files in this release come essentially in pairs: one is the 1-dimensional spectrum in fits format, the second one is the corresponding spectral preview (.png) showing the position of key absorption and emission lines if a redshift is available, along with the 2-dimensional spectrum. For each unique target we also provide a colour image cutout (.jpg; 5"x5", derived from ACS B, V, i z images) centered on the target. For the fits spectrum all relevant parameters are included in the FITS header (see an example here) which have been designed to be consistent with other VO compliant releases of ESO Advanced Data Products.

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

   GOODS_FORS2_GDS_xx_bb_v3.0.fits 1-d Fits file
   GOODS_FORS2_GDS_xx_bb_v3.0.spec.png Spectrum preview
   GOODS_FORS2_GDS_xx_v3.0.img.jpg Colour image cutout

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_v3.0.fits
For stacked spectra, which are combinations of observations from different masks we omit the mask ID:

   GOODS_FORS2_GDS_xx_v3.0.fits 1-d Fits file
   GOODS_FORS2_GDS_xx_v3.0.spec.png Spectrum preview

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

   GOODS_FORS2_GDS_RELEASE3.0_TABLE.tab Ascii table
   GOODS_FORS2_GDS_RELEASE3.0_DS9.tsv DS9 Catalogue
   GOODS_FORS2_GDS_RELEASE3.0_FITS.fits FITS table
   GOODS_FORS2_GDS_RELEASE3.0_VOTABLE.xml VOTable

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

Data retrieval

There are two modes of retrieval for the GOODS/FORS2 Release 3.0:
One can either retrieve the entire data set (the data tables, the preview products and the 1-d FITS spectra; 4668 files packaged in a 77 MB tar file),
or, alternatively, it is also possible to get the data tables only (listing the basic data and redshifts).

Acknowledgements

When using data products provided in this release, we request acknowledgement of the ESO/GOODS project and referring to the publications Vanzella et al. 2005, A&A, 434, 53, "The Great Observatories Origins Deep Survey. VLT/FORS2 spectroscopy in the GOODS-South Field", Vanzella et al. 2006, A&A, 454, 423, "The Great Observatories Origins Deep Survey - VLT/FORS2 Spectroscopy in the GOODS-South Field - Part II", and Vanzella et al. 2007, A&A, accepted, "The Great Observatories Origins Deep Survey - VLT/FORS2 Spectroscopy in the GOODS-South Field: Part III". Please also use the following statement in your articles when using these data: