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First Data Release, Version 2

The NDWFS first data release (DR1) consists of photometrically zero-pointed and astrometrically calibrated FITS images generated from our multiple Bw, R, and I-band images of the four NW sub-fields of the Boötes Field of the NOAO Deep Wide-Field Survey. The four sub-fields are named as follows:

The positions of these fields are given in the following table.

All images included in this first release were obtained with the KPNO Mayall 4m telescope and MOSAIC-I imager. The R-band images were obtained with an early version of the instrument that was equipped with engineering grade CCDs. The Bw-band and I-band images were obtained after the original CCDs had been replaced with thinned, more sensitive devices. However, for the I-band observations of these particular four sub-fields we have not yet obtained the originally planned 200 minutes, or 3.33 hours, of total exposure time. For the bulk of the survey sub-fields total I-band integration times of 200 minutes are being obtained, but due to the high sky brightness during solar max (when most of the observations have been made), we are still not reaching our original goal for the depth of the I-band images.

Conditions for the observations of some of these fields were below average compared to the rest of the NDWFS images obtained to date. In particular, delivered image quality and the night sky brightness in these images are both sub-par for observations included in this release. The OH emission was particularly strong on one night, adversely affecting the I-band images of two of the four released fields. Details on the data reduction procedures are available in the draft guide to processing NDWFS survey data. Our current web pages will be expanded with additional information as time permits.

Astrometric solutions were generated as described in our reduction notes using the USNO A2.0 catalogue and USNO astrometric standard fields. A more complete description of these procedures is in preparation and will be linked off of these pages when it is completed. The typical RMS of the residuals of these solutions is 0.35 arcseconds.

Version 2 of the first data release uses images stacked with exposure time weighting of the individual input images to produce an approximate 1/variance weighting resulting in improved signal-to-noise. The v02 release also includes net exposure masks (_exp.fits suffix) and net rejected images masks (_nrej.fits) in addition to the bad pixel masks (_bpm.fits).

Photometric Zero-points and Limiting Magnitudes

The images of a given filter being released today have over-lap regions of approximately one arcminute that allow us to ensure that their relative calibration is accurate to better than 0.03 of a magnitude. The absolute zero-points have been determined using multiple observations of Landolt standards on photometric nights. The images were either obtained on photometric nights, zero-pointed by separate exposures obtained for that purpose, or tied (using the over-lap regions) to fields observed under photometric conditions.

The photometry in this image has been referenced to Kron-Cousins
B-band, based on observations of Landolt standards on 1999/04/14UT.
The photometric solution is Bmag = m_inst + MAGZERO - 0.093(B-R).

The photometry in this image has been referenced to Kron-Cousins
R-band, based on observations of Landolt standards on 1998/04/04UT.
The photometric solution is Rmag = m_inst + MAGZERO + 0.068(R-I).

The photometry in this image has been referenced to Kron-Cousins
I-band, based on observations of Landolt standards on 1999/03/28UT.
The photometric solution is Imag = m_inst + MAGZERO + 0.039(R-I).

We have in general been describing our survey depths in both Vega and AB magnitudes. In the tables below, we show the photometric zero points (and limits) in both Vega and AB units. The zero-points were derived on the Vega system, adn the AB values are only approximate, as they will depend on the color of any particular object of interest. Note in particular that while Bw observations of spectrophotometric standards indicate that the AB_zeropoint and Vega_zeropoint for this filter are very similar, our current values have been referenced to B-band Landolt standards. A more complete discussion of our photometry is in preparation and will be linked off of this page in the future.

                  Kron-Cousins Photometric Zeropoint 
               (Magnitude of one count in the FITS Image)
Sub-Field           Bw-band     R-band     I-band
                   to B-band)
NDWFS J1426+3531    32.738      30.635     31.631
NDWFS J1426+3456    32.682      30.701     31.110
NDWFS J1428+3531    32.760      30.614     31.765
NDWFS J1428+3456    32.575      30.567     30.244

            RMS in ADU of Sky/Limiting Kron-Cousins Magnitude 
            Defined as the 5-sigma limit in a 2'' Diameter Apt.
Sub-Field           Bw-band     R-band     I-band
NDWFS J1426+3531  6.12/26.93  3.62/25.40  11.94/25.10
NDWFS J1426+3456  6.05/26.89  4.22/25.30  11.09/24.66
NDWFS J1428+3531  6.11/26.96  3.41/25.44  16.61/24.87
NDWFS J1428+3456  5.33/26.92  4.53/25.09   8.64/24.06

                       AB Photometric Zeropoint 
               (AB Magnitude of one count in the FITS Image) 
Sub-Field           Bw-band     R-band     I-band 
NDWFS J1426+3531    32.738      30.835     32.131
NDWFS J1426+3456    32.682      30.901     31.610
NDWFS J1428+3531    32.760      30.814     32.265
NDWFS J1428+3456    32.575      30.767     30.744

                    RMS in ADU of Sky/Limiting AB Magnitude 
               Defined as the 5-sigma limit in a 2'' Diameter Apt.
Sub-Field           Bw-band     R-band     I-band
NDWFS J1426+3531  6.12/26.93  3.62/25.60  11.94/25.60
NDWFS J1426+3456  6.05/26.89  4.22/25.50  11.09/25.16
NDWFS J1428+3531  6.11/26.96  3.41/25.64  16.61/25.37
NDWFS J1428+3456  5.33/26.92  4.53/25.29   8.64/24.56

                     Total Exposure Time in hours/
                  Number of Exposures in Combined Images
Sub-Field           Bw-band     R-band     I-band
NDWFS J1426+3531    2.10/9      1.7/10     3.00/18
NDWFS J1426+3456    2.33/10     1.2/7      2.14/17
NDWFS J1428+3531    2.33/10     1.7/10     2.22/15
NDWFS J1428+3456    2.33/10     1.7/10     2.59/51

Delivered Image Quality

The combined images currently available were made from individual exposures with a range of delivered image quality. We did not try to match or circularize the PSF's of either the final combined images taken with different filters, nor the images that went into the final images. This might limit the usefulness of these images for some studies (e.g. weak lensing analysis). A report quantifying these limitations is in preparation and will be linked off this web page when it has been completed.

There is also some variation in image quality across the field. Still, we can roughly characterize the DIQ (delivered image quality)as determined by measurements of the FWHM of stars in the release images as follows.

                   FWHM in pixels      FWHM in arcseconds
Sub-Field          Bw    R     I       Bw     R      I
NDWFS J1426+3531   4.5   6.0   5.2     1.16   1.55   1.34
NDWFS J1426+3456   5.0   4.5   4.0     1.29   1.16   1.03
NDWFS J1428+3531   5.6   5.2   2.6     1.45   1.34   0.67
NDWFS J1428+3456   6.0   4.9   5.1     1.55   1.26   1.32

NOAO Deep Wide-Field Survey -- Last modified: February 29 2016 16:18:52. -- Feedback: jannuzi@noao.edu