10 March 2010

Multi-object spectroscopy of faint galaxies in the Chandra Deep Field South (CDFS) has been carried out, as part of the Great Observatories Origins Deep Survey (GOODS), using the VIsible Multi-Object Spectrograph (VIMOS) instrument mounted at the Melipal Unit Telescope of the VLT at ESO's Cerro Paranal Observatory, Chile. The GOODS/VIMOS spectroscopic campaign is part of the ESO/GOODS program in the CDFS, which complements the FORS2 ESO/GOODS spectroscopic campaign.This data release contains the redshift catalog resulting from the full data set of the GOODS/VIMOS spectroscopic campaign of the ESO/GOODS large programme 171.A-3045 (P.I. C. Cesarsky) which have been obtained in service mode observations between September 2004 and January 2007. The GOODS/VIMOS campaign is structured in two separate surveys using two different VIMOS grisms. The VIMOS Low Resolution Blue (LR-Blue) and Medium Resolution (MR) orange grisms have been used to cover different redshift ranges. The LR-Blue campaign is aimed at observing galaxies mainly at 1.8<z<3.5, while the MR campaign mainly aims at galaxies at z<1 and Lyman Break Galaxies (LBGs) at z >3.5</p> <p>The full GOODS/VIMOS spectroscopic campaign consists of 20 VIMOS masks. <span class=">Reduced data products from the first 12 masks were part of the first release and described in Popesso et al. 2009. This second release completes the whole VIMOS campaign by adding 8 new masks to the previous release. In total we obtained 5052 spectra, 3634 from the 10 LR-Blue masks and 1418 from the 10 MR masks. A significant fraction of the extracted spectra comes from serendipitously observed sources: ~21% in the LR-Blue and ~16% in the MR masks. We obtained 2242 redshifts in the LR-Blue campaign and 976 in the MR campaign for a total success rate of ~62% and ~69% respectively, which increases to ~66% and ~73% if only primary targets are considered. The typical redshift uncertainty is estimated to be σ_z~0.0012 (~255 km/s) for the LR-Blue grism and σ_z~0.0004 (~120 km/s) for the MR grism.

A full description of the survey can be found in the accompanying publication "The Great Observatories Origins Deep Survey - VLT/VIMOS Spectroscopy in the GOODS-South Field: Part II" by Balestra et al. (2010), A&A 512, A12.

• Overview and survey layout
• Release content
• Release notes
• Data format
• Data retrieval
• Acknowledgements

Overview and survey layout

Spatial distribution of objects from the whole (LR-Blue plus MR grism) GOODS/VIMOS spectroscopic campaign (red circles) over the ESO-WFI R-band image. The contours outline the area of the 2 Ms exposure of the CDFS and the GOODS-S field.

The GOODS/VIMOS survey has been designed to complement the GOODS/FORS2 spectroscopic survey (Vanzella et al. 2005, 2006, 2008) in terms of completeness and sky coverage. The target selection is based on the multiwavelength photometry available for the GOODS-S field. Different criteria have been used for the low resolution LR-Blue grism and the medium resolution MR Orange grism. According to the usable wavelength ranges targets with estimated redshifts between 1.8 and 3.8 have been selected for observations with the VIMOS LR-Blue grism, targets with redshift z < 1 or 2.8 < z < 4.8 have been selected for observations with the VIMOS MR Orange grism. A magnitude cut R < 25 AB has been applied to the LR-Blue targets. Please refer to Popesso et al. (2009) and Balestra et al. (2010) for a detailed description of the target selection procedure.

Release content

Summary of reduced VIMOS observations

The VLT/VIMOS spectroscopic observations were carried out in service mode during ESO observing periods P74-P78. A log of all the GOODS/VIMOS observations is presented in Table 1. The total exposure time per mask is 4 h. Each LR-Blue mask consists of 10 exposures of 24 min, while each MR mask consists of 12 exposures of 20 min. All the masks were designed with 1 arcsec slits. The spatial scale for VIMOS is 0.205 arcsec/pixel.

In the LR-Blue campaign, the LR-Blue grism was used together with the Order Sorting OS_Blue cutoff filter. In this configuration the useful wavelength range is 3700-6700 Å, the nominal resolution is R=λ/Δλ=180, corresponding to a spectral resolution of ~28 Å, and the dispersion is 5.7 Å/pixel.

The MR grism and the GG475 filter were used in the MR campaign. In this configuration the useful wavelength range is 4800-10000 Å, the nominal resolution is R=580, which corresponds to a spectral resolution of ~13 Å, and the dispersion is 2.55 Å/pixel.

The total number of GOODS/VIMOS spectra extracted is 3634 in the LR-Blue and 1418 in the MR campaign. We have identified 3305 single LR-Blue objects and 1297 single MR objects. Out of those, we were able to determine 2074 and 885 redshifts in the LR-Blue and the MR campaign, respectively.

The following table shows the breakdown by redshift quality class.

In analogy to the complementary GOODS/FORS2 redshift campaign, we defined four quality flags to indicate the quality of a redshift estimate as follows:

• flag A, high quality, i.e. several emission lines and strong absorption features are well identified;
• flag B, intermediate quality, i.e. at least two spectral features are well identified, for instance one emission line plus few absorption features;
• flag C, low quality, i.e. spectral features, either in emission or in absorption, are less clearly identified;
• flag X, no redshift estimated. No features identified.

The reliability of VIMOS LR-Blue redshifts with quality flag A, B, and C is estimated to be approximately 100%, 60%, and 20% confidence level, respectively. VIMOS MR quality flag-A, -B, and -C redshifts are estimated to be reliable at approximately 100%, 95%, and 60% confidence level, respectively.

Release Notes

Data reduction method

The pipeline processing of the GOODS/VIMOS data was carried out using the VIMOS Interactive Pipeline Graphical Interface (VIPGI, Scodeggio et al. 2005). Details of the data reduction and analysis are fully described in the papers "The Great Observatories Origins Deep Survey - VLT/VIMOS Spectroscopy in the GOODS-South Field", Popesso et al. 2009, A&A, 494, 443 and "The Great Observatories Origins Deep Survey - VLT/VIMOS Spectroscopy in the GOODS-South Field: Part II", Balestra et al. 2010.

Comparison to previous releases

This data release, which is the second of this survey, complements the previous data release 1.0. It adds 8 new masks to the previous release (12 masks, Popesso et al. 2009). This release contains the final merged redshift catalog based on both releases 1.0 and 2.0 superseding the redshift catalog being part of the previous release. Note that the assignment of GOODS/VIMOS identification numbers has not been altered with the new release, so that the targets may be identified unambiguously. We also added in the new catalogs a label to easily distinguish between the two releases. A few redshifts of data release 1.0 have been updated as described in the accompanying publication (Balestra et al. 2010). It is worth noticing that uncertain coordinates for a small number (18 LR-Blue and 16 MR) of serendipitous objects in DR1 were improved in DR2, as described in Balestra et al. (2010). Moreover, 63 LR-Blue and 18 MR serendipitous objects in DR1 having uncertain coordinates and no redshift estimate were removed from the final DR2 catalogs.

Version 2.0.1 constitutes a minor revision of the previous data release v2.0 from 15 December 2009. 14 spectra that have been mistakenly missing in v2.0 were added, three spectra were revised, the redshift for one object was changed, and the redshift catalog was updated accordingly.

Data format

For each spectrum the following data products are being released: the 1-dimensional spectrum in FITS format and the corresponding plot of the spectrum in postscript format.

The following naming convention has been adopted for the individual files:

where <bb> indicates the mask ID of the observation, quadrant, slit and object number. For convenience the data products of this release (version 2.0) are kept separated from the data products of the first release (version 1.0). Data are packed in two tarballs containing the LR-Blue spectra and the MR spectra, respectively.

The redshift catalogs are being released in ASCII table format and include the entire GOODS/VIMOS campaign. The two redshift catalogs contain the following information: (column 1) the coordinate-based GOODS identification number, where the coordinates used are those of the matching WFI object, (column 2) the VIMOS identification number, (columns 3-4) the coordinates of the matching WFI object, (columns 5-6) the original VIMOS coordinates, (columns 7-10) B- and R-band WFI magnitudes with the corresponding errors, (columns 11-12) z₈₅₀ GEMS magnitudes and corresponding errors, (column 13) redshift, (column 14) quality flag, (column 15) comments and identified spectral features, (column 16) a label for primary or secondary (i.e. serendipitous) objects, and (column 17) a label to distinguish between the first and second VIMOS release. All magnitudes are given in the AB system.

We release 4 catalogs: the catalogs labelled GOODS_VIMOS_Release2.0_*_table.dat are cleaned for duplicate observations of the same object, in which case we kept the best redshift estimate (with the only exception of objects having two quality-C redshifts, in which case we kept both estimates), while the catalogs labelled GOODS_VIMOS_Release2.0_*_fulltable.dat contain the complete set of observations including duplicates.

Data release version 2.0.1 adopts exactly the same convention regarding filenames. The update package contains the following files:

Please request your copy of the data from the ESO Science Archive using the data request submission form.

Data retrieval

The data from the GOODS/VIMOS spectroscopic campaign can be requested as packages from the ESO archive using the table below. For convenience, one data package has been prepared for each release. Note that subsequent data releases complement each other. This means, for instance, that all the packages 1.0, 2.0, and 2.0.1 have to be requested one after the other in order to obtain the complete set of spectra. Otherwise, supposing you have already downloaded data release 1.0 earlier, you just need to request the packages 2.0 and 2.0.1 to obtain the full set. Likewise, if you have already the data releases 1.0 and 2.0 on your local disk, you just need to request package 2.0.1 for updating your data set to the most recent version. However, subsequent versions of the associated redshift catalog supersede each other, that is, the most recent redshift catalog, v2.0.1 currently, makes all previous versions obsolete.

Please choose the data release and make your selection of files on the data request pages linked to below.

Note that any redshift and target position information in the headers of the spectra of release version 1.0 have been superseded by the information in the catalogues of release versions 2.0 and 2.0.1.

Acknowledgements

When using data products provided in this release, we request acknowledgement of the ESO/GOODS project and referring to the related publication "The Great Observatories Origins Deep Survey - VLT/VIMOS Spectroscopy in the GOODS-South Field: Part II" by Balestra et al. (2010), A&A 512, A12. Please also use the following statement in your articles when using these data: