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As part of the Great Observatories Origins Deep Survey (GOODS),
near-infrared imaging observations of the
South (CDF-S) are being carried out in J, H, Ks bands, using the
instrument mounted at the Antu Unit Telescope of the VLT at ESO's Cerro
Paranal Observatory, Chile.
These data are being obtained as part of the ESO Large Programme: LP168.A-0485(A) (PI: C. Cesarsky). Data covering four ISAAC fields in J and Ks bands are also available from the ESO programmes 64.O-0643, 66.A-0572 and 68.A-0544 (PI: E.Giallongo), which were part of the previous data releases.
Since ISAAC observations are still ongoing, this release consists of J, H and Ks images of fields that have already been completed and are available in the ESO Science Archive Facility up to the end of ESO observing period 73 (effectively March 2005).
This data release includes 24 fully reduced VLT/ISAAC fields in J and Ks bands, covering 159.1 and 159.7 arcmin2 of the GOODS/CDFS region, respectively, and -- new in this release -- 19 fields in H band covering 126.7 arcmin2, as well as three mosaics in the J, H and Ks bands. The data were reduced and prepared for release by the Advanced Data Products group in the Virtual Observatory Systems department.
of ISAAC tiles included in this release is overlayed on the HST/ACS
mosaic: 21 tiles in the J, H and Ks bands (cyan, thick), 5 additional
in the J and Ks bands (cyan, thin). Each ISAAC field is 2.5
Further observations in the red tiles are scheduled for 2005 (P75).
[Click to get full size image]
being released are tabulated to the right,
consisting of 69 images in J (24), H (19) and Ks (26) bands,
and photometrically calibrated. The table gives: in column (1) the field number; in column (2) the passband; in column (3) the total integration time in seconds;
in column (4) the seeing
measurement in arcsec; in column (5) the RMS zero point error; in column (6)
of frames that make up the final image; in column (7) the period of
observations; in column (8) the 1-sigma sky background limit (AB) measured
in circular apertures of 0.7 arcsec diameter. The same table
is also available in ASCII format.
In addition, we release for convenience the full mosaic of all ISAAC tiles in J, H and Ks bands (see figures above) with an accurate astrometric solution and uniform photometric zero point (however, read the notes below).
[click to see to the full table]
to previous releases
This release is the third of this survey. It revises and significantly extends the previous v1.0 release of April 30, 2004. The first release consisted of 8 fields in J, H and Ks (Fields 09, 10, 11, 14, 15, 16, 20, 21). The previous release consists of a new reduction of these same 8 fields, with the addition of 13 new fields in J-band and 15 new fields in Ks. The present release contains 3 new fields in J and Ks bands (Fields 06, 18, and 29) and 19 new fields in H band. Besides these 25 new images this release also includes the re-reduced data of all the previously released fields. With respect to the previous release (V1.0) the exposure times of the re-reduced images are slightly smaller in many cases due to a more stringent screening and rejection of poor quality reduction blocks.
Note the suffix 'n' (new) for the fields 25n and 26n is due to a re-arrangement of the ISAAC mosaic in the initial stage of survey to ensure maximum coverage of the GOODS/CDFS area within the time allocation. Reduced observations in the original field positions (as part of programme ID 168.A-0485(E)) are also included in this release (~5 hours in Ks band only in fields named F25,26).
The main areas of improvements in this release are:
The present release superseeds the previous ESO/GOODS data releases version 0.5 and version 1.0.
Anticipated future releases will focus on the
remaining ISAAC/GOODS fields (01, 02, 12, 17, 28, 32) for the J and Ks
band, the completion of the H band coverage, and the ZP evaluation from
observations of photometric standard stars.
Each field is the co-addition of a
number of sky-subtracted frames (NCOMBINE in the image
header) grouped in a number of Reduction Blocks.
Images are registered using an accurate astrometric grid
defined by an R-band ESO Wide Field Imager (WFI) image of the
Astrometric Solution: The astrometric calibration was derived using a reference catalog generated from a deep R-band WFI image which was astrometrically calibrated using the Guide Star Catalog GSC2.3. The astrometry has been compared by the GOODS team with calibrated data from the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS). These comparisons yield rms scatter in astrometry of 0.1'' across the entire area.
All images have a pixel scale of 0.15", which is exactly a factor of five larger than the pixels in the GOODS/ACS images.Photometric Zero Points (ZPs): The photometric calibration of the present data is based on the image mosaics in J, Ks and H constructed from a mosaic of photometrically calibrated SOFI images of the EIS-DEEP and DPS infrared surveys conducted over the same region (Vandame et al. 2001). The SOFI images (5'x5') encompass a number of tiles of the ISAAC mosaic (2.5'x2.5' each), yielding more robust relative calibration across the entire surveyed area. A ZP for each ISAAC field was determined from the SOFI images using a sample of ~400 ``stars'' which have been identified in the HST/ACS images based on SExtractors stellarity index and flux ratio. All ISAAC images were first PSF-matched to the value of the corresponding SOFI image (~0.9 arcsec) employing Gaussian convolution, then aperture magnitudes of these stars were used to determine a ZP for each individual tile in the AB system. Between 3 and 12 sources per tile have been used.
This procedure yielded ZPs with RMS scatters ranging between 0.01 and 0.06 mag in J-band, 0.01 and 0.08 mag in Ks-band and up to 0.17 mag in H-band. These numbers also account for systematic uncertainties inherent to the calibration procedure due to e.g. residual non-uniformities in the images (either ISAAC or SOFI).
For those tile where less than three isolated stars were available for accurate photometry all high signal-to-noise sources which appear pointlike in the ISAAC images based on a FWHM criterion were used for the calibration.
The resulting RMS zeropoint errors are given for each image of the three bands
J, H, and Ks, respectively.
However, note that to provide a homogeneous photometric ZP across the entire GOODS field, we have rescaled all images to the same ZP of 26.0 in the AB system. Corresponding keywords in the fits headers have been set accordingly, PHOTZP=26.0, PHOTSYS=AB, and PHOTZPER. The exposure times are also normalized to unity (EXPTIME=1), so that AB magnitudes in all released fields, including the mosaics, can be obtained as: mag(AB)=-2.5*Log(flux)+ZP. The following AB corrections have been used: JAB=JVega+0.90, HAB=HVega+1.38, and Ks,AB=Ks,Vega+1.86.
To determine systematic errors in this calibration procedure,
independent/crossed photometric calibrations are needed on the SOFI and
ISAAC data. The SOFI ZPs were found consistent
(within a few percent)
photometry of a limited number of stars in the field.
comparison of the present release data with photometric catalogs from
Saracco et al. 2001 (J and Ks band), Cimatti et al.
2002 (Ks band) and Moy et al. 2003 (H band) did not reveal
any systematic difference taking into account the given error margins.
The evaluation of ZPs from observations of photometric standard stars (available in the ESO Archive) is planned in future releases. We encourage the user community to communicate to the GOODS/EIS team any relevant information on this topic.
Image Mosaics: in addition to the individual image tiles, this release also includes mosaics of the co-adjoined tiles as single fits files in J, H and Ks bands, as well as corresponding weight-maps. The WCS information and accuracy of the individual tiles is preserved in these mosaics. A uniform ZP of 26.0 can be used (e.g. with SExtractor) across the entire field, however, it is important to note that the PSF varies from tile to tile within each mosaic (see table below). In the absence of proper aperture corrections or PSF matching procedures, this would impact efforts to create multi-color catalogs. The J, H and Ks mosaics have slightly different dimensions, however they can be readily registered using the intrinsic WCS information.
The following file naming convention has been adopted:
for the field number <xx>
in the band <b> and the
respective weight map;
for the mosaic image in the band <b> and the respective weight map.
names can be found in the OBJECT keywords in the FITS
See here the complete list of data files belonging to this release as they can be retrieved via the data request page.
comments to <email@example.com>
Last update: Oct 03, 2005