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Third Data Release (DR3) -- Boötes Field Optical and ONIS K-band Images and Catalogues

The NDWFS third data release (DR3) consists of the photometrically and astrometrically calibrated FITS images and associated data quality masks and images for all of the Mosaic-1 optical (Bw, R, I) and ONIS K-band imaging obtained for the 27 sub-fields that comprise the Boötes Field of the NOAO Deep Wide-Field Survey.

The images can be obtained via the NOAO Science Archive or through the links below. The catalogues are currently only available through the links below, but we are in the process of enabling their availability through other methods as well. These will be noted on the NDWFS Home page when available.

Data Files Overview

The optical and near-IR data sets comprising this release have been organized to be similar in appearance (similar file names, structures, etc.), but do have significant differences.

The entire DR3 data set can be downloaded, but please note these are large files! The images and mask files (i.e. not including catalogues) takes up approximately 96 GB. An image cutout function will be available shortly which will allow image regions of arbitrary size to be created on-the-fly and downloaded via the web. The NSA already provides the ability to request a section of a particular image, but does not yet allow the simultaneous request of cut-outs from multiple images.

Access to the NDWFS DR3 images (and associated sigma, sig, and rms files) is available via the NOAO archive FTP server.

In this directory the files with names that start with "NDWFS" are the combined/stacked images as well as the associated sigma (for the optical images), sig (for the IR images), and rms images. These files are described more completely below and in the rest of the documentation linked off these pages. You should also be able to access these files via anonymous ftp to archive.noao.edu. Change directories to /ndwfs/dr3/ and transfer the files. Under this main directory (/ndwfs/dr3/) are two directories with additional files associated with the images. These are masks and can be downloaded either as FITS BINARY TABLES (cd to /ndwfs/dr3/masksfits/) or IRAF pixel list files (cd to /ndwfs/dr3/masks/). These are described briefly below.

Access to the NDWFS DR3 mask files in IRAF pixel list format (.pl).

Access to the NDWFS DR3 mask files in FITS BINARY TABLE format.

Note that for some applications the user might want a FITS image of one of the mask files, and not a FITS BINARY TABLE or .pl format of the file. Using IRAF you can convert between these formats as follows:
cl> imcopy orig.pl fitsBinTable.fits[type\=mask]
will convert the .pl format to FITS BINARY TABLE format
cl> imcopy fitsBinTable.fits[1] new.pl
will convert the FITS BINARY TABLE format to a .pl format and
cl> imcopy orig.pl new.fits
will convert the .pl format to a FITS image

Access to the NDWFS DR3 catalogues is available here.

NDWFS Source Naming Conventions

Optical Data Files

Here we briefly describe the optical imaging data files that are available. During the end of October 2004 the web pages describing this data release will be expanded to more completely describe the data set. For each of the 27 sub-fields there is a FITS image that is the stack of multiple individual KPNO 4m Mosaic-1 images. There are also six associated files for each of these images (with suffixes "_bpm", "_exp", "_nrej", "_ncomb", "_sigma", and "_rms") which are briefly described below and will be discussed in more detail on these web pages in the future.

If you obtain the files from the NSA they will all be in FITS format (images and mask files). If you obtain them from the link above, the some of the mask files will also be in the IRAF .pl (pixel list) format. The FITS images and IRAF pixel list masks available above are named according to the following convention:


    "NDWFS" Stands for the NOAO Deep Wide-Field Survey
    "J"rrrrpdddd Denotes the IAU J2000 RA and DEC of the sub-field of the survey and does not necessarily match the image center position, which is defined in the image header World Coordinate System
    f Indicates the filter (Bw, R, I, or K)
    id Indicates the version number of the released data. For the optical data in DR3, all files have been given the version number _03. For four of the sub-fields (those in the NE corner of the Boötes field), earlier versions of these same data have been released previously. The DR3 (_03) versions should be used to take advantage of improved photometric calibration and stacking of the images. If any changes are made to released images any such changes will be logged on these web pages

The "_bpm.fits" (or identical file, different format, "_bpm.pl") files are "bad pixel mask" files. Any region where valid data contributed to the stack has a value of 0 while the remainder of the mask has a value of 1. Regions found in the bad pixel mask are typically edges of the field and "bleed trails" of saturated pixels from bright stars.

Files with the "_exp.fits" suffix (or "_exp.pl", which is an identical file in content presented in the IRAF pixel list format) are "exposure mask" files. They contain the net exposure time in seconds for a given region of an image. The net exposure time varies across the image due to the rejection of bad pixels and the dithering (change in pointing of the telescope) between exposures that contributed to the stacked image. Regions where the exposure mask values vary significantly include edges of the subfields and areas which fell between the mosaic camera CCD chips in several images contributing to the final stacks.

Files with the "_nrej.fits" (or identical file, different format, "_nrej.pl") suffix are "rejection mask" files. For a given pixel in the combined image, the value of NCOMBINE (one of the header keywords) minus the value of the associated pixel in the rejection mask indicates the number of images that contributed to the value of that pixel in the combined image. These are similar to the "_rjm.pl" files of the version 1 release except they are in FITS rather than IRAF "pixel list" format.

Files with the "_ncomb.fits" suffix (or identical file, different format, "_ncomb.pl") contains the number of images that contributed to the determination of the value of that pixel. This is equivalent to the number NCOMBINE (one of the header keywords) minus the associated value of the _nrej file.

Files with the "_sigma.fits" suffix contain the root-mean-square of the pixel values in the individual exposures that contributed to the stack at that position. It is not an estimate of the uncertainty in the value at that pixel in the combined (stacked) image.

The value of each pixel in the files with the "_rms.fits" suffix is the uncertainty (in ADU) in the combined (stacked) image at the corresponding pixel and were constructed from the "_sigma.fits" file and the "_ncomb.fits" file (sigma/sqrt(ncomb)).

IR Data Files

Like the documentation describing the optical imaging, the available information about the IR imaging and data products will be expanded over the next few weeks (see the link above). For now, please keep in mind the following differences between the optical and IR data sets. First, the ONIS K-band imaging does not cover the entire Boötes field, but only approximately 60 percent of the area (the entire field has been observed, using FLAMINGOS, and those images are nearly ready for release). The individual K-band images used to build the stacked/combined images were much smaller than those obtained in the optical. We have chosen to combine the smaller IR images into stacks 40 arcminutes by 40 arcminutes, centered roughly at the same positions as the optical stacks. Using the optical sub-field map as reference, there is complete or partial ONIS K-band coverage for 20 of the 27 Boötes sub-fields. Second, while we were able to obtain photometric zero-point observations for those optical images obtained under non-photometric conditions, this was not generally possible for the IR imaging. As a result, some regions of the K-band survey lack photometric data. These are identifiable through the "_exp" files, which show the exposure time of photometric data at each pixel in a stacked image. Non-photometric data was only included in a stack where no photometric data was available.

For each of the 20 sub-fields with ONIS K-band data, there is a FITS image and six supporting files. These include the following:

"_bpm.fits" (or _bpm.pl) -- bad pixel mask. In practice, given the large number of images contributing to each stack, very few if any pixels in the combined image are "bad". Note that pixels near bright stars that might not have been responding linearly would not be noted in this file.

"_exp.fits" (or _exp.pl) -- exposure mask file (units seconds). Note that this applies to the number of seconds of photometric data contributing to the image stack at each pixel. Non-photometric data is included only in those regions where photometric data is not available.

"_nrej.fits" (or _nrej.pl) -- same definition as for the optical images

"_ncomb.fits" (or _ncomb.pl) -- contains the number of images that contributed to the determination of the value of that pixel in the combined stack.

"_sig.fits" -- sigma image (rms of the pixels that went int the final stack)

"_rms.fits" -- rms image (rms of the final image as determined from (sig)/(sqrt(ncomb))

"_flag.fits" (or _flag.pl) -- flag image constructed for use with SExtractor, used to generate the catalogues for DR3. This is the same as _ncomb.pl, except that it contains zeros where the data were not photometric.

Catalogues Overview

Access to the NDWFS DR3 catalogues is available here.

Single-band and matched catalogues have been generated to accompany this data release. A partial discussion of the properties of these catalogues is here . This discussion will be expanded during the end of October and early November and will be presented in some detail for the optical and IR catalogues in respectively Jannuzi et al. 2005 and Dey et al. 2005 (these papers will be linked off this web page when available). All NDWFS catalogues for the October 22, 2004 Bootes data release (DR3) were generated with SExtractor 2.3.2 (Bertin & Arnouts 1996, A&A 117, 393). Catalogs were generated in single-band mode for each subfield and band. These catalogues are available in both ASCII and FITS binary table format. Matched catalogues (a simple attempt to identify sources detected in more than one band) were also generated and are available.

These catalogues are intended for preliminary science with the NDWFS data. We caution that they may not be ideal for all the science possible with the NDWFS imaging dataset. Results derived from the catalogs should, at the very least, be confirmed by inspecting the imaging data.

The single sub-field/single-band catalogues have names that are derived from the image from which they were constructed. For example, NDWFSJ1426p3236_R_03.cat.gz is a compressed ASCII file of the SExtractor generated catalogue of our R-band image of sub-field NDWFS J1426+3236. There are a total of 101

The matched catalogue files have names like NDWFS_R_32_33.cat_m.gz. See here for further description.

(The compressed (gzip) ASCII version of the catalogue files takes approximately 5.3 GB (117 files; 101 files for the single-band per sub-field catalogues; 16 files making up the matched catalogue). The compressed (gzip) FITS version of the same catalogues takes up about 6.5 GB.)

NOAO Deep Wide-Field Survey -- Last modified: November 26 2007 13:00:53. -- Feedback: jannuzi@noao.edu