Spitzer Documentation & Tools

FLS-SDSS Version Information

    These data are assembled, calibrated, mosaiced, and arranged by a set of IDL (6.0) and C code in four CVS modules at Princeton and NYU. The current version of the downloadable data is:

    • version 1_0_2

    The current version was created with the following tag versions of the following CVS modules:

    module nameCVS tag location
    sirtf v1_0_2NYU
    photoop v1_1_3Princeton
    idlutils v4_10_8Princeton

FLS-SDSS Image Mosaic Properties

    • 5-band ugriz visual image mosaics composed of hundreds of SDSS drift-scan fields
    • sets of four 1.75 deg × 1.25 deg mosaics, north-up
    • each mosaic is 15912×11364
    • 0.396 arcsec × 0.396 arcsec square pixels (at fiducial point RA=259.5 deg, Dec=59.5 deg J2000)
    • correct, FITS-compliant WCS astrometry headers
    • the four mosaics “snap together” into one immense (31824×22728) mosaic with no overlaps or edge distortion issues
    • calibrated in intensity units of [nMgy (0.396 arcsec)-2], where 1 nMgy (“nano maggie”) in flux is equivalent to 22.5 mag (AB system)

    NB: If a source in one of the mosaics is measured to have total flux N in nMgy, its magnitude m is then

    m = [22.5 mag] - 2.5 log10 N .

    The above files are unwieldy, so we have made some lower-resolution, single-field mosaics with the following properties:

    • same 5 bands
    • individual 3.5 deg × 2.5 deg mosaics, north-up
    • each mosaic is 10608×7576
    • 1.188 arcsec × 1.188 arcsec square pixels (at fiducial point RA=259.5 deg, Dec=59.5 deg J2000)
    • correct, FITS-compliant WCS astrometry headers
    • calibrated in intensity units of [nMgy (1.188 arcsec)-2]

    NB: Unlike the high resolution images, these lower-resolution images are not band-limited and should be used with caution.

    There are some defects in these mosaics, which need to be worked out, worked around, or avoided by scientific users:

    • sky noise variance is not constant but varies inversely with the number of overlapping SDSS fields (1 or 2 for most of the image area); in particular there are diagonal “stripes” of low noise in the images where SDSS camera columns overlap
    • sky background level is not exactly zero everywhere; use local sky estimation when photometering sources
    • bright stars are saturated and have bleed trails
    • the PSF is variable across the fields
    • filter reflections in the SDSS cameras cause bright stars to show nearby flares in sky brightness
    • some cosmic rays have slipped through
    • small CCD readout defects near extremely bright sources
    • many bright single-band satellite trails

FLS-SDSS Spectroscopy

    We have also assembled all SDSS spectroscopy in the FLS region into a pair of FITS files:

    • one FITS file containing all of the SST FLS region SDSS spectra and their observational uncertainties on a common wavelength grid, with common calibration
    • one FITS binary table file containing the positions of the spectroscopic sources and all of the parameters derived from the SDSS spectra by the Princeton pipelines

    Essentially everything a user needs to know about the format and contents of these files, including calibration, is available at the Princeton/MIT SDSS Spectroscopy page.

SDSS Photometric Catalog