1 December 2004
Survey ..................... XMM
Telescope .................. ESO/MPG 2.2m
Instrument ................. WFI
Program IDs ................ 170.A-0789; 70.A-0529; 71.A-0110
Origin ..................... ESO/EIS
Number of regions .......... 8
Region ..................... Selected XMM Serendipitous Survey
Number of Fields ........... 8
Passbands .................. B; V; R; I
Number of Filters........... 4
EIS Release Number ......... 24
Version .................... 0.9
Total Data Volume .......... 212 Mb
Release Date ............... December 2004
Release prepared by ........ EIS team, L. F. Olsen, C. Benoist
Product Type ............... Catalogs from Stacked Images
Number of catalogs ......... 28
Data Volume ................ 212 Mb
Origin ..................... ESO/EIS
Number of regions........... 12
Region ..................... Selected XMM Serendipitous Survey
Number of Fields ........... 12
Passbands .................. B; V; R; I
EIS Release Number.......... 22
Release Date................ 04 November 2004
PRODUCTS IN PREVIOUS RELEASE
Product Type................ Image Stacks
Number of Stacked Images.... 44
Based on ideas submitted by the ESO community and evaluated by ESO's Survey Working Group (SWG), the XMM survey (administered by the ESO Imaging Survey (EIS) and the Public Survey Group (PSG) teams) consists of follow-up optical observations of the XMM-Newton Serendipitous Sky Survey (XSSS) using the ESO Wide Field Imager (WFI) at the ESO/MPG 2.2m telescope at the La Silla Observatory. This survey seeks to obtain WFI images in the B-, V-, R- and I- passbands (for minimum spectral discrimination and photometric redshift determination) of XMM fields publicly available in the XMM archive. The fields were selected and prioritized by a collaboration of interested parties from the XMM Survey Science Centre (SSC), the Bonn group (led by P. Schneider) and an appointed committee of the SWG. The observations were originally proposed to cover a total area of approximately 10 square degrees (40 fields) to a limiting magnitude of 25 (AB, 5 sigma, 2 arcsec aperture, see original proposal presented by the SWG to the OPC).
Data for the XMM survey are being provided by:
The present release consists of an initial version of science-grade, single-passband (SPB) object catalogs extracted from ``final'' stacked images produced for 8 XMM fields ( EIS release number 22) located at galactic latitudes |b| > 15 degrees. 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.
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 XMM-Newton follow-up survey, and follows earlier releases of night products and final stacked images.
The present release consists of 28 science grade (S/N > 5), extinction corrected catalogs extracted using SExtractor from fully calibrated ESO/MPG 2.2m WFI stacked images in B-, V-, R- and I- passbands for 8 out of the 12 fields released so far, located at galactic latitudes |b| > 15 degrees. Details about the images can be found in release number 22.
The catalogs being released were extracted from images similar but not identical to those released in release number 22. 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 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. 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 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, 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 are 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 22.
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 19. Based on these photometric calibrations the photometric zeropoints of the stacked images were derived, as described in the release number 22, 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 28 catalogs being released, 13 were graded A, 10 B, 4 C, and 1 D. In contrast to the images, the catalog graded D is also being released in order to illustrate the impact of inadequate de-fringing. It is important to note that the catalog graded D was extracted from a grade C image. 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||XMM-10||PB5062||R#844||D||Fringing leading to severe problems (spurious detections all over the image)|
|2||XMM-08||NGC4666||V#843||C||Missing masks for a few saturated stars. Spurious objects around large central galaxies.|
|3||XMM-09||Q1246-057||B#878||C||Spurious objects around large bright galaxy at the top right corner. Cosmic rays misidentified as real objects.|
|4||XMM-09||Q1246-057||V#843||C||Large number of spurious objects around large bright galaxy at the top right corner|
|5||XMM-09||Q1246-057||I#879||C||Large number of spurious objects around large bright galaxy at the top right corner and due to multiple reflection rings.|
|6||XMM-05||BPM16274||B#878||B||Masks missing around a few saturated stars. Some cosmic rays misidentified as real objects.|
|7||XMM-03||HE1104-1805||B#878||B||Masks missing for a few saturated stars|
|8||XMM-07||LBQS_2212-1759||R#844||B||Spurious objects at the corners caused by insufficient trimming|
|9||XMM-04||MS1054.4-0321||V#843||B||Masks missing for a few saturated stars|
|10||XMM-08||NGC4666||B#878||B||Masks missing for a few saturated stars|
|11||XMM-08||NGC4666||I#879||B||Spurious objects around large central galaxies|
|12||XMM-06||SHARC-2||B#878||B||Slight tilt of the image causes trimming frame to not mask completely the borders|
|13||XMM-06||SHARC-2||V#843||B||Insufficient de-blending near bright galaxies but over de-blending near bright stars|
|14||XMM-06||SHARC-2||R#844||B||Insufficient de-blending near bright galaxies|
|15||XMM-06||SHARC-2||I#879||B||Insufficient de-blending around bright galaxies. Spurious objects caused by bright stars reflection features and stray light reflections|
Not surprisingly, there is a strong correlation between the grade of the catalogs and the grade of the images from which they were extracted.
The quality of the photometric calibration of the reduced and stacked images have been assessed in the EIS release number 19 and 22 , 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 eighth of 2004, and number 24 since March 1998. It is the first 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 ranging from from 0.08 to 0.15 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. 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