7 December 2004
Survey ..................... DPS
Telescope .................. ESO/MPG 2.2m
Instrument ................. WFI
Program IDs ................ 169.A-0725; 67.A-0244(A); 164.O-0561
Origin ..................... ESO/EIS
Number of regions .......... 3
Region ..................... DEEP1; DEEP2; DEEP3
Number of Fields ........... 11
Passbands .................. U (2); B; V; R; I (2)
Number of Filters .......... 7
EIS Release Number ......... 25
Version .................... 0.9
Release Date ............... December 2004
Release prepared by ........ EIS team, L. F. Olsen
Product Type ............... Catalogs from Stacked Images
Number of catalogs ......... 40
Data Volume ................ 340 Mb
Origin ..................... ESO/EIS
Number of regions........... 3
Region ..................... DEEP1; DEEP2; DEEP3
Number of Fields ........... 11
Passbands .................. U (2); B; V; R; I (2)
EIS Release Number.......... 23
Release Date................ 10 November 2004
PRODUCTS IN PREVIOUS RELEASE
Product Type ............... Stacked Images
Number of Stacked Images ... 40
Based on ideas submitted by the ESO community and evaluated by ESO's Survey Working Group (SWG), the DPS survey, administered by the ESO Imaging Survey (EIS) and Public Survey Group (PSG) teams, comprises three optical and infrared strategies. The optical part consists of a deep survey covering three regions of 1 square degree on the sky, in U-, B-, V-, R- and I-passbands, using the wide-field imager (WFI) mounted on the ESO/MPG 2.2m telescope at La Silla. Each of the three DEEP regions -- 1, 2, 3 -- is covered by four WFI pointings (in five passbands) -- a, b, c, d -- per region. The regions were selected both to enable observations year-round and because they overlapped with regions of other scientific interest. For instance, DEEP1 was chosen to complement the deep ATESP radio survey carried out with the Australia Telescope Compact Array (ATCA) covering the region surveyed by the ESO Slice Project, while DEEP2 included the CDF-S field. Finally, DEEP3, was chosen in the northern galactic hemisphere, thus providing an almost year-round coverage (see the original proposals for more details). The location and the characteristics of the surveyed regions as well as the planned limiting magnitudes in each passband can be found in the DPS strategy page. One should be aware that in an attempt to improve the performance of the survey, new U and I filters were purchased and used during the course of the observations (see below).
The data contributing to the present release were obtained as part of the ESO Large Programme: 164.O-0561, carried out in visitor mode, and its service mode continuation (30 hours) 169.A-0725 (Principal Investigator: J. Krautter, as chair of the SWG), complemented by V- and R-band observations from the following ESO programme (Principal Investigator: P. Schneider): 67.A-0244, covering the DEEP-1 region.
The present release consists of an initial version of science-grade, single-passband (SPB) object catalogs extracted from ``final'' stacked images produced for 11 DPS fields ( EIS release number 23). The catalogs were extracted using the SExtractor program (Bertin & Arnouts 1996), graded and the results of preliminary statistical analysis compared to those obtained by other authors, in order to characterize and validate them. These results are presented, whenever possible, in the product log associated with each catalog. These logs are accessible from the release WEB page.
The present release, together with release #24, should be considered beta-releases of object catalogs. Fine-tuning of input parameters, improvement of procedures and an assessment of the quantities being reported in the catalog may prove necessary, and may depend on the specific application. Feedback from users on these as well as other topics would be extremely helpful an dmay justify revisions.
For more information about the terminology and conventions used in this document refer to the WEB README pages.
This is the third official release of reduced data (not including revisions) for the DPS survey, and follows earlier releases of night products (# 20) and final stacked images (#23).
The present release consists of 40 science grade (S/N > 5), extinction corrected catalogs extracted using SExtractor from fully calibrated ESO/MPG 2.2m WFI stacked images in U-, B-, V-, R- and I- passbands for the 11 fields released so far. Details about the images can be found in release number 23.
The catalogs being released were extracted from images similar but not identical to those released in release number 23. The images were re-created because, as explained in the COMMENTS of that release, the parameter for the cosmic ray rejection was inadequate, leading to a very noisy weight map. However, as also explained there, the impact on the catalogs is negligible.
Official EIS products can be retrieved via two alternate routes, both originating at the EIS home page. These procedures are described elsewhere (see Retrieving EIS Products). It is worth reiterating that to request data users have to be registered with the ESO Science Archive.
In the case of the present release the "data release information section" is followed by a section detailing the "contents" of the release, listing:
Note: All data products are subject to revision and update once released. A report of the changes, if there are any, may be found in the ``COMMENTS'' field next to the particular release (in the release WEB page) and/or in the READMEs of the revised release.
For each survey product the EIS system prepares a ``product'' log from which the process log and the configuration file used can be accessed and inspected (not yet fully implemented). Currently, the product log associated to a science-grade, SPB catalog comprise four distinct sections represented in the rendering of the HTML. All sections have a ``Product Identification'' sub-section which, among other things, identifies the user that created the product, the type and main attributes like passband and exposure time. This sub-section is reproduced so as to enable a proper identification of the information if these pages are printed separately (not currently possible). The sections in the product log are:
Even though the product logs are still not in their final form, the logs available in the present release serve to illustrate the type of information the system is able to provide to survey users and is a vital complement to the catalog itself.
In the upper right corner of the data release WEB page for catalogs one finds a button (properties) which link to plots showing the distribution of some of the quantities that characterize the catalogs (e.g. the grade attributed to the catalogs; 80% completeness magnitude in the AB system, number of objects, galaxies and stars and number density of objects in the science grade catalog)
Since the infrastructure is still under development, currently plots are being produced without adequate description. It is foreseen that these plots will be embedded into HTML files providing captions and statistics.
The catalogs being released are in the FITS format, based on the ``Leiden Data Center'' (LDAC) convention originally adopted by the DENIS project and later expanded in the course of the EIS project. It currently consists of a FITS header and the following tables: FIELDS, OBJECTS, MASK and FILTER.
Currently, the FIELDS table consists of 109 columns. These include: 1) basic information set by the LDAC library; 2) keywords taken from the FITS header of the image from which the catalog was extracted; 3) the main SExtractor configuration parameters used; and 4) information computed by the EIS Data Reduction system. The latter includes, for instance:
Some of the information contained in the FIELDS table is also available in the ``Product Log''. In the future, embedding the product log into the FITS format of the catalog should be considered to avoid duplication of the information and facilitate distribution.
The OBJECTS table reports the parameters characterizing the extracted objects, as computed by SExtractor. Currently, there are 69 columns, some of which represented by vectors (e.g. aperture magnitudes). The choice of apertures and the flags defined are the result of suggestions made by users of EIS data products and they may evolve in time. In addition to the SExtractor flag, the values of which are described in the proper manual, 14 other flags have been defined to facilitate the filtering of the catalogs. To the this end the following flags have been added:
Feedback from users regarding the parameters is welcome.
The MASK table gives the number and coordinates of the vertices of both automatically created masks as well as those drawn by hand using a SKYCAT plug-in. Saturated objects are always masked. In addition, the user has the option of also masking objects brighter than a user-specified magnitude. The size of the mask scales with the major-axis of the object, as computed by SExtractor. The scaling factor is specified by the user. The adopted shape of the mask is a square with one of the diagonals oriented north-south in an attempt to mask the diffraction spikes. The parameters used in the mask definition are reported in the product log.
The FILTER table gives the filter transmission curve and the total convolved optical system response function. In the future, it will also include some of the basic characteristics associated with the filter such as the ESO identification number, effective wavelength, and FWHM of the filter.
This is the first release of single passband catalogs for these fields and therefore no comparison data are available.
This release represents a first set of catalogs extracted from WFI images and created systematically using the EIS Data Reduction/Survey System infrastructure in a fully un-supervised manner. The input images are final stacked images produced from the nightly reduced images. These images were astrometrically and photometrically calibrated as described in release number 23.
Catalogs were extracted using the SExtractor program (version 2.3.2) and a common configuration file, with the option of using the weight-map associated to each image. Some of the critical SExtractor configuration parameters are reproduced in the FIELDS table of the catalog itself. For each object extracted, 69 parameters are given describing the main geometric and photometric properties of the objects. The parameters were chosen as a compromise between the total number of parameters and the most frequently requested parameters from survey product users.
The first catalog to be extracted is a very low S/N catalog, which contains a large number of spurious objects. Starting from this catalog, a final science-grade catalog is produced by:
Note that except for objects with S/N less than that required, no object is removed from the catalog. If necessary, these objects can be pruned by the user according to the flags described above. In addition, the default magnitude system adopted for the objects can be changed using the information available in the FIELDS table.
The accuracy of the astrometric calibration relies on the astrometric calibration of the reduced images and the reference catalog used. As described in previous releases, it is typically better than 250 mas.
The reduced images were calibrated to the Vega magnitude system based on observations of Landolt (1992) standard stars as described in release number 20. Based on these photometric calibrations the photometric zeropoints of the stacked images were derived, as described in the release number 23, where more details concerning the accuracy of the photometric calibration can be found.
Before being released the catalogs overlayed on the images were examined by eye and graded by the EIS team, with the grade range being from A (best) to D (worst). The grade is meant as a subjective indication of the quality of the catalog. Additional information about the validity of the catalog can e found in the verification section of the associated product log.
Out of the 40 catalogs being released, 8 were graded A, 23 B, 7 C, and 2 D. In contrast to the images, two catalogs graded D are also being released in order to illustrate the impact of inadequate de-fringing. It is important to note that the catalogs graded D were extracted from grade C images. The table below presents all cases where comments were made. The table, ordered by increasing grade, lists: in column (1) entry number; in column (2) the region name; in column (3) the EIS field name; in column (4) the passband; in column (5) the grade; and in column (6) a comment.
|#||Region||EIS Field Name||Passband||Grade||Comment|
|1||DEEP1||DEEP1a||I#845||D||Fringing leads to multiple spurious detections|
|2||DEEP2||DEEP2b||I#845||D||Fringing leads to multiple spurious detections|
|5||DEEP2||DEEP2a||R#844||C||Large number of spurious objects caused by very bright star at the lower left edge of the image. Missing masks around a few saturated stars|
|6||DEEP2||DEEP2c||I#845||C||Reflections from bright stars cause spurious objects in various areas of the image. Low level fringing adds also additional noise in the catalog|
|7||DEEP2||DEEP2d||R#844||C||Numerous cosmic rays misidentified as real objects. Spurious caused by reflection ring of bright star in the lower left quadrant.|
|8||DEEP3||DEEP3b||I#845||C||Multiple spurious detections at the lower left quadrant due to fringing|
|9||DEEP3||DEEP3c||R#844||C||Missing masks for a few saturated stars. Multiple spurious objects caused by the reflection rings of the bright stars at the top and bottom right of the image|
|10||DEEP3||DEEP3c||I#845||C||Spurious objects caused by fringing at the lower left quadrant of the image. Multiple spurious objects caused by the reflection rings of bright stars at the top and bottom right of the image.|
|11||DEEP3||DEEP3d||I#879||C||Spurious objects caused by multiples reflection rings/stray light across the image.|
|12||DEEP1||DEEP1a||U#877||B||Spurious objects around bright stars|
|13||DEEP1||DEEP1a||U#841||B||Few spurious objects around bright stars|
|14||DEEP1||DEEP1a||B#842||B||Mask missing for a few saturated stars|
|15||DEEP1||DEEP1b||U#877||B||Masks missing around saturated stars. Spurious objects around bright stars.|
|16||DEEP1||DEEP1b||I#845||B||Residual fringing increases the number of spurious|
|17||DEEP1||DEEP1c||V#843||B||Masks missing around a few saturated stars|
|18||DEEP1||DEEP1c||R#844||B||Masks missing around a few saturated stars|
|19||DEEP2||DEEP2b||U#877||B||Masks missing around all saturated stars|
|20||DEEP2||DEEP2b||B#842||B||Spurious objects caused by reflections of bright star at center top of the image. Missing masks for several saturated stars|
|21||DEEP2||DEEP2b||V#843||B||Spurious objects caused by reflections of bright stars at the top center and lower right corner of the image.|
|22||DEEP2||DEEP2c||U#877||B||Missing masks for a few saturated stars|
|23||DEEP2||DEEP2c||U#841||B||Missing masks around a few saturated stars|
|24||DEEP3||DEEP3a||U#877||B||Spurious objects around bright stars. Spurious objects caused by stray light at the top left corner.|
|25||DEEP3||DEEP3a||U#841||B||Spurious objects around bright stars. Spurious objects caused by stray light at the top left corner.|
|26||DEEP3||DEEP3a||B#842||B||Masks missing for a few saturated stars. Spurious objects caused by stray light at the top left corner.|
|27||DEEP3||DEEP3a||V#843||B||Masks missing for a few saturated stars. Spurious objects caused by stray light at the top left corner|
|28||DEEP3||DEEP3a||R#844||B||Masks missing for a few saturated stars. Spurious objects caused by stray light at the top and bottom left corners.|
|29||DEEP3||DEEP3b||U#877||B||Spurious objects around bright stars|
|30||DEEP3||DEEP3b||B#842||B||Missing masks around a few saturated stars|
|31||DEEP3||DEEP3b||V#843||B||Masks missing around a few saturated stars|
|32||DEEP3||DEEP3b||R#844||B||Spurious objects caused by left-over cosmic rays at the inter-chip gaps|
|33||DEEP3||DEEP3c||U#877||B||Spurious objects around bright stars|
|34||DEEP3||DEEP3c||V#843||B||Multiple spurious objects caused by the reflection ring of the bright stars at the top and bottom right of the image|
|38||DEEP1||DEEP1b||R#844||A||Mask missing around 1 saturated star at the center-right of the image|
|39||DEEP2||DEEP2b||R#844||A||Few spurious at the lower right corner caused by bright star reflection at the edge of the image.|
In general, there is a correlation between the grade of the catalogs and the grade of the images from which they were extracted. However, the catalogs grade can be lower than that of the image due to effects such as the detection of large number of spurious objects associated with the ghost images of brigth stars, stray light, and others. For instance, all the U-band catalogs were graded B. As in the case of the corresponding images, the I-band catalogs are typically C and D.
The quality of the photometric calibration of the reduced and stacked images have been assessed in the EIS release number 20 and 23 , respectively, and will not be repeated here.
The magnitudes of the final catalog have been converted into the AB magnitude system and corrected for the galactic extinction using Schlegel et al. (1998).
The attributes of the catalogs are summarized in distribution of grades, the 80% completeness limiting magnitude in the Vega system, the number of objects, galaxies and stars, and number density of objects. The color code adopted for the filters (passbands) here and elsewhere is as follows: B (blue); V (green); R (red), I (magenta). This color coding is consistent with that adopted in previous releases. The first panel shown in black is a combination of all filters.
Comparison with other authors
The reduced data (in the form of stacks) were also compared to results obtained using the GaBoDS pipeline (Schirmer et al. 2003) and Erben et al. (2004) developed by the Bonn group. Extensive and repeated comparisons were made between SExtractor-produced catalogs from the images generated by these two independent systems. Initial discrepancies, resulting from the different techniques used (e.g. cosmic ray removal, gain-harmonization) were resolved, leading at the end to results in excellent agreement.
Originally, the following releases were scheduled:
Unfortunately, since the EIS project is scheduled to terminate on December 31, 2004 the EIS team will not be able to complete the work until then.
This release is the nineth of 2004, and number 25 since March 1998. It is the second release of science-grade catalogs extracted from stacked products created using the framework of the EIS Data Reduction/Survey System. Each catalog has an associated product log which provides complementary information about the product as well as the results of some simple analyzes carried out to characterize and validate the catalog. The production of the catalogs was done in a completely un-supervised way, with a throughput of about 0.1 Mpix/sec, a good match to the data rate of other parts of the pipeline. It is important to emphasize that as one goes down the chain of survey products, the more complex they become making it difficult to assign a quality for all possible applications. Fine-tuning of parameters may also prove necessary, and may depend on the specific application. This, however, requires several iterations which due to time constrains cannot be presently carried out. Feedback from users would be extremely helpful.
Arnouts, S. et al. , 2001, A&A, 179, 436
Bertin, E. & Arnouts, S., A&AS, 117, 393
Erben, T. et al. , 2004, in preparation
Girardi, L., et al. , 2004, A&A, submitted
Landolt, A. U., 1992 Astronomical Journal 104, 340
Schlegel, D., Finkeiner, D., & Davis, M., 1998, ApJ, 500, 525
Vandame, B. et al. , 2004, in preparation
Vandame, B., 2004, PhD thesis, in preparation