Legacy Survey Files

Throughout this page <region> denotes either north for BASS/MzLS or south for DECaLS.

Directory Structures

At NERSC (for collaborators)

Top level directory:
/global/cfs/cdirs/cosmo/data/legacysurvey/dr9/
Top level directory for DECaLS data:
/global/cfs/cdirs/cosmo/data/legacysurvey/dr9/south/
Top level directory for MzLS/BASS data:
/global/cfs/cdirs/cosmo/data/legacysurvey/dr9/north/
Top level directories for sweeps catalogs:
/global/cfs/cdirs/cosmo/data/legacysurvey/dr9/south/sweep/
/global/cfs/cdirs/cosmo/data/legacysurvey/dr9/north/sweep/

Summary Files

survey-bricks.fits.gz

FITS binary table with the RA, Dec bounds of each geometrical "brick" on the sky. This includes all bricks on the sky, not just the ones in our footprint or with coverage in DR9. For that information, see the next file description.

Column Type Description
BRICKNAME char[8] Name of the brick.
BRICKID int32 A unique integer with 1-to-1 mapping to brickname.
BRICKQ int16 A "priority" factor used for processing.
BRICKROW int32 Dec row number.
BRICKCOL int32 Number of the brick within a Dec row.
RA float64 RA of the center of the brick.
DEC float64 Dec of the center of the brick.
RA1 float64 Lower RA boundary.
RA2 float64 Upper RA boundary.
DEC1 float64 Lower Dec boundary.
DEC2 float64 Upper Dec boundary.

<region>/survey-bricks-dr9-<region>.fits.gz

A FITS binary table with information that summarizes the contents of each brick for a region of DR9.

Column Type Description
brickname char[8] Name of the brick.
ra float64 RA of the center of the brick.
dec float64 Dec of the center of the brick.
nexp_g int16 Median number of exposures in the unique area (i.e. BRICK_PRIMARY area) of the brick in g-band.
nexp_r int16 Median number of exposures in the unique area of the brick in r-band.
nexp_z int16 Median number of exposures in the unique area of the brick in z-band.
nexphist_g int32[6] Histogram of number of pixels in the unique brick area with 0, 1, 2, 3, 4, or > 5 exposures in g.
nexphist_r int32[6] Histogram of number of pixels in the unique brick area with 0, 1, 2, 3, 4, or > 5 exposures in r.
nexphist_z int32[6] Histogram of number of pixels in the unique brick area with 0, 1, 2, 3, 4, or > 5 exposures in z.
nobjs int16 Total number of BRICK_PRIMARY objects in this brick, of all types.
npsf int16 Total number of BRICK_PRIMARY objects in this brick, of type PSF.
nsimp int16 Total number of BRICK_PRIMARY objects in this brick, of type SIMP (there should be 0 such objects).
nrex int16 Total number of BRICK_PRIMARY objects in this brick, of type REX.
nexp int16 Total number of BRICK_PRIMARY objects in this brick, of type EXP.
ndev int16 Total number of BRICK_PRIMARY objects in this brick, of type DEV.
ncomp int16 Total number of BRICK_PRIMARY objects in this brick, of type COMP (there should be 0 such objects).
nser int16 Total number of BRICK_PRIMARY objects in this brick, of type SER.
ndup int16 Total number of BRICK_PRIMARY objects in this brick, of type DUP.
psfsize_g float32 Median PSF size, in arcsec, evaluated at the BRICK_PRIMARY objects in this brick in g-band.
psfsize_r float32 Median PSF size, in arcsec, evaluated at the BRICK_PRIMARY objects in this brick in r-band.
psfsize_z float32 Median PSF size, in arcsec, evaluated at the BRICK_PRIMARY objects in this brick in z-band.
psfdepth_g float32 5-sigma PSF detection depth in \(g\)-band (AB mag), using PsfEx PSF model.
psfdepth_r float32 5-sigma PSF detection depth in \(r\)-band (AB mag), using PsfEx PSF model.
psfdepth_z float32 5-sigma PSF detection depth in \(z\)-band (AB mag), using PsfEx PSF model.
galdepth_g float32 5-sigma galaxy (0.45" round exp) detection depth in \(g\)-band (AB) mag.
galdepth_r float32 5-sigma galaxy (0.45" round exp) detection depth in \(r\)-band (AB) mag.
galdepth_z float32 5-sigma galaxy (0.45" round exp) detection depth in \(z\)-band (AB) mag.
ebv float32 Median SFD98 dust map E(B-V) extinction, in magnitudes, evaluated at BRICK_PRIMARY objects in this brick.
trans_g float32 Median Milky Way dust transparency in \(g\)-band, based on ebv. See also MW_TRANSMISSION_G.
trans_r float32 Median Milky Way dust transparency in \(g\)-band, based on ebv. See also MW_TRANSMISSION_R.
trans_z float32 Median Milky Way dust transparency in \(z\)-band, based on ebv. See also MW_TRANSMISSION_Z.
cosky_g float32 Estimated sky level in the coadded images (stacks) in \(g\)-band [1].
cosky_r float32 Estimated sky level in the coadded images (stacks) in \(r\)-band.
cosky_z float32 Estimated sky level in the coadded images (stacks) in \(z\)-band.
ext_g float32 Extinction in \(g\)-band.
ext_r float32 Extinction in \(r\)-band.
ext_z float32 Extinction in \(z\)-band.
wise_nobs int16[4] Number of images that contributed to WISE calculations in each filter (not profile-weighted).
trans_wise float32[4] Median Milky Way dust transparency in WISE bands, based on ebv. See also, e.g., MW_TRANSMISSION_W1.
ext_w1 float32 Extinction in \(W1\)-band.
ext_w2 float32 Extinction in \(W2\)-band.
ext_w3 float32 Extinction in \(W3\)-band.
ext_w4 float32 Extinction in \(W4\)-band.
brickid int16 A unique integer with 1-to-1 mapping to brickname.
ra1 float32 Lower RA boundary.
ra2 float32 Upper RA boundary.
dec1 float32 Lower Dec boundary.
dec2 float32 Upper Dec boundary.
area float32 Area of the brick in square degrees.
survey_primary boolean True for northern (southern) bricks that lie in the northern (southern) region of the Legacy Surveys.
in_desi boolean True if the brick is in the DESI footprint.

Note that, for the nexphist rows, pixels that are masked by the NOIRLab Community Pipeline as, e.g., cosmic rays or saturation (see, e.g. the ALLMASK/ANYMASK information on the DR9 bitmasks page), do not count toward the number of exposures. More information about the morphological types and MW_TRANSMISSION can be found on the catalogs page.

survey-ccds-<camera>-dr9.fits.gz

A FITS binary table with almanac information about each individual CCD image for each camera (where <camera> is one of 90prime for BASS, decam for DECaLS or mosaic for MzLS).

This file contains information regarding the photometric and astrometric zero points for each CCD of every image that is part of the DR9 data release. Photometric zero points for each CCD are computed by identifying stars and comparing their instrumental magnitudes to color-selected stars in the PanSTARRS "qz" catalog.

The photometric zeropoints (zpt, ccdzpt, etc) are magnitude-like numbers (e.g. 25.04), and indicate the magnitude of a source that would contribute one count per second to the image. For example, in an image with zeropoint of 25.04 and exposure time of 30 seconds, a source of magnitude 22.5 would contribute \(30 \times 10^{((25.04 - 22.5) / 2.5)} = 311.3\) counts.

Column Type Description
image_filename char[120] Path to FITS image, e.g. "north/DECam_CP/CP20170729/c4d_170730_045351_ooi_g_v1.fits.fz".
image_hdu int16 FITS HDU number in the image_filename file where this image can be found.
camera char[X] The camera that took this image (X is 7 for "90prime", 6 for "mosaic" and 5 for "decam").
expnum int64 Exposure number, eg 348224.
plver char[8] Community Pipeline (CP) version number.
procdate char[19] CP processing date.
plprocid char[7] Unique, time-based, CP processing hash - see the plprocid page for how to convert this to a date.
ccdname char[X] CCD name, e.g. "N10", "S7" for DECam (X is 4 for 90prime and mosaic CCDs, and 3 for decam).
object char[35] Name listed in the object tag from the CCD header.
propid char[10] Proposal ID of the program that took this image, eg "2014B-0404".
filter char[1] Filter used for observation, eg "\(g\)", "\(r\)", "\(z\)".
exptime float32 Exposure time in seconds, eg 30.
mjd_obs float64 Date of observation in MJD (in UTC system), eg 56884.99373389.
airmass float32 Airmass of observation (measured at the telescope bore-sight).
fwhm float32 FWHM (in pixels) measured by the CP.
width int16 Width in pixels of this image, eg 2046.
height int16 Height in pixels of this image, eg 4096.
ra_bore float64 Telescope boresight RA of this exposure (deg).
dec_bore float64 Telescope boresight Dec of this exposure (deg).
crpix1 float32 Astrometric header value: X reference pixel.
crpix2 float32 Astrometric header value: Y reference pixel.
crval1 float64 Astrometric header value: RA of reference pixel.
crval2 float64 Astrometric header value: Dec of reference pixel.
cd1_1 float32 Astrometric header value: transformation matrix.
cd1_2 float32 Astrometric header value: transformation matrix.
cd2_1 float32 Astrometric header value: transformation matrix.
cd2_2 float32 Astrometric header value: transformation matrix.
yshift boolean (ignore; it's always False).
ra float64 Approximate RA center of this CCD (deg).
dec float64 Approximate Dec center of this CCD (deg).
skyrms float32 Sky rms for the entire image (in counts/second).
sig1 float32 Median per-pixel error standard deviation, in nanomaggies.
ccdzpt float32 Zeropoint for the CCD (AB mag).
zpt float32 Median zero point for the entire image (median of all CCDs of the image), eg 25.0927.
ccdraoff float32 Median astrometric offset for the CCD <GAIA-Legacy Survey> in arcsec.
ccddecoff float32 Median astrometric offset for the CCD <GAIA-Legacy Survey> in arcsec.
ccdskycounts float32 Mean sky counts level per second per pixel (AVSKY divided by EXPTIME) in the CP-processed frames measured (with iterative rejection) for each CCD in the image section [500:1500,1500:2500].
ccdskysb float32 Sky surface brightness (in AB mag/arcsec2).
ccdrarms float32 rms in astrometric offset for the CCD <Gaia-Legacy Survey> in arcsec.
ccddecrms float32 rms in astrometric offset for the CCD <Gaia-Legacy Survey> in arcsec.
ccdphrms float32 Photometric rms for the CCD (in mag).
phrms float32 Median photometric rms across all CCDs in the image (in mag).
ccdnastrom int16 Number of stars (after sigma-clipping) used to compute astrometric correction.
ccdnphotom int16 Number of Gaia+PS1 stars detected with signal-to-noise ratio greater than five.
ccd_cuts int32 Bit mask describing CCD image quality (see the DR9 bitmasks page).

survey-ccds-<camera>-dr9.kd.fits

As for the survey-ccds-<camera>-dr9.fits.gz files but limited by the depth of each observation. These files contain the CCDs actually used for the DR9 reductions. Columns are the same as for the survey-ccds-<camera>-dr9.fits.gz files.

ccds-annotated-<camera>-dr9.fits.gz

Versions of the survey-ccds-<camera>-dr9.fits.gz files with additional information gathered during calibration pre-processing before running the Tractor reductions.

Includes all of the columns in the survey-ccds-<camera>-dr9.fits.gz files plus the columns listed below. Note that string columns can have different lengths in the survey-ccds-<camera>-dr9.fits.gz and ccds-annotated-<camera>-dr9.fits.gz files. For example the camera column can change from char[9] to char[7] (see, e.g. legacypipe issue #379).

Column Type Description
annotated boolean True unless there is an error when computing the "annotated" quantities in this row of the file
good_region int16[4] If only a subset of the CCD images was used, this array of x0,x1,y0,y1 values gives the coordinates that were used, [x0,x1), [y0,y1). -1 for no cut (most CCDs)
ra0 float64 RA coordinate of pixel (1,1)...Note that the ordering of the CCD corners is detailed here
dec0 float64 Dec coordinate of pixel (1,1)
ra1 float64 RA coordinate of pixel (1,H)
dec1 float64 Dec coordinate of pixel (1,H)
ra2 float64 RA coordinate of pixel (W,H)
dec2 float64 Dec coordinate of pixel (W,H)
ra3 float64 RA coordinate of pixel (W,1)
dec3 float64 Dec coordinate of pixel (W,1)
dra float32 Maximum distance from RA,Dec center to the edge midpoints, in RA
ddec float32 Maximum distance from RA,Dec center to the edge midpoints, in Dec
ra_center float64 RA coordinate of CCD center
dec_center float64 Dec coordinate of CCD center
meansky float32 Our pipeline (not the CP) estimate of the sky level, average over the image, in nanomaggies
stdsky float32 Standard deviation of our sky level, in nanomaggies
maxsky float32 Max of our sky level, in nanomaggies
minsky float32 Min of our sky level, in nanomaggies
pixscale_mean float32 Pixel scale (via sqrt of area of a 10x10 pixel patch evaluated in a 5x5 grid across the image), in arcsec/pixel.
pixscale_std float32 Standard deviation of pixel scale
pixscale_max float32 Max of pixel scale
pixscale_min float32 Min of pixel scale
psfnorm_mean float32 PSF norm = 1/sqrt of N_eff = sqrt(sum(psf_i^2)) for normalized PSF pixels i; mean of the PSF model evaluated on a 5x5 grid of points across the image. Point-source detection standard deviation is sig1 / psfnorm.
psfnorm_std float32 Standard deviation of PSF norm
galnorm_mean float32 Norm of the PSF model convolved by a 0.45" exponential galaxy.
galnorm_std float32 Standard deviation of galaxy norm.
psf_mx2 float32 PSF model second moment in x (pixels^2)
psf_my2 float32 PSF model second moment in y (pixels^2)
psf_mxy float32 PSF model second moment in x-y (pixels^2)
psf_a float32 PSF model major axis (pixels)
psf_b float32 PSF model minor axis (pixels)
psf_theta float32 PSF position angle (deg)
psf_ell float32 PSF ellipticity 1 - minor/major
humidity float32 Percent humidity outside
outtemp float32 Outside temperate (deg C).
tileid int32 tile number, 0 for data from programs other than MzLS or DECaLS
tilepass uint8 tile pass number, 1, 2 or 3, if this was an MzLS or DECaLS observation, or 0 for data from other programs. Set by the observers (the meaning of tilepass is on the status page)
tileebv float32 Mean SFD98 E(B-V) extinction in the tile, 0 for data from programs other than BASS, MzLS or DECaLS
ebv float32 SFD98 E(B-V) extinction for CCD center
decam_extinction float32[6] Extinction for optical filters \(ugrizY\)
wise_extinction float32[4] Extinction for WISE bands W1,W2,W3,W4
psfdepth float32 5-sigma PSF detection depth in AB mag, using PsfEx PSF model
galdepth float32 5-sigma galaxy (0.45" round exp) detection depth in AB mag
gausspsfdepth float32 5-sigma PSF detection depth in AB mag, using Gaussian PSF approximation (using seeing value)
gaussgaldepth float32 5-sigma galaxy detection depth in AB mag, using Gaussian PSF approximation

ccds-annotated-<camera>-dr9.kd.fits

As for the ccds-annotated-<camera>-dr9.fits.gz files but limited by the depth of each observation. These files contain the CCDs actually used for the DR9 reductions. Columns are the same as for the ccds-annotated-<camera>-dr9.fits.gz files.

<region>/dr9-<region>-depth.fits.gz

A concatenation of the depth histograms for each brick, for each region, from the coadd/*/*/*-depth.fits tables. HDU1 contains histograms that describe the number of pixels in each brick with a 5-sigma AB depth in the given magnitude bin. HDU2 contains the bin edges of the histograms.

  • HDU1
Column Type Description
counts_ptsrc_g int32[50] Histogram of pixels for point source depth in \(g\) band
counts_gal_g int32[50] Histogram of pixels for canonical galaxy depth in \(g\) band
counts_ptsrc_r int32[50] Histogram of pixels for point source depth in \(r\) band
counts_gal_r int32[50] Histogram of pixels for canonical galaxy depth in \(r\) band
counts_ptsrc_z int32[50] Histogram of pixels for point source depth in \(z\) band
counts_gal_z int32[50] Histogram of pixels for canonical galaxy depth in \(z\) band
brickname char[8] Name of the brick
  • HDU2
Column Type Description
depthlo float32 Lower bin edge for each histogram in HDU1 (5-sigma AB depth)
depthhi float32 Upper bin edge for each histogram in HDU1 (5-sigma AB depth)

<region>/dr9-<region>-depth-summary.fits.gz

A summary of the depth histogram for a region of DR9. FITS table with the following columns:

Column Type Description
depthlo float32 Lower limit of the depth bin
depthhi float32 Upper limit of the depth bin
counts_ptsrc_g int64 Number of pixels in histogram for point source depth in \(g\) band
counts_gal_g int64 Number of pixels in histogram for canonical galaxy depth in \(g\) band
counts_ptsrc_r int64 Number of pixels in histogram for point source depth in \(r\) band
counts_gal_r int64 Number of pixels in histogram for canonical galaxy depth in \(r\) band
counts_ptsrc_z int64 Number of pixels in histogram for point source depth in \(z\) band
counts_gal_z int64 Number of pixels in histogram for canonical galaxy depth in \(z\) band

The depth histogram runs from magnitude of 20.1 to 24.9 in steps of 0.1 mag. The first and last bins are "catch-all" bins: 0 to 20.1 and 24.9 to 100, respectively. The histograms count the number of pixels in each brick's unique area with the given depth. These numbers can be turned into values in square degrees using the brick pixel area of 0.262 arcseconds square. These depth estimates take into account the small-scale masking (cosmic rays, edges, saturated pixels) and detailed PSF model.

Random Catalogs (randoms/*)

randoms-1-*.fits

Twenty files of random points sampled across the CCDs that comprise the geometry of DR9. Random locations were generated across the footprint at a density of 2,500 per square degree and meta-information about the survey was extracted from pixels at each random location from files in the coadd directory (see below, e.g. coadd/*/*/*-depth-<filter>.fits.fz, coadd/*/*/*-galdepth-<filter>.fits.fz, coadd/*/*/*-nexp-<filter>.fits.fz, coadd/*/*/*-maskbits.fits.fz, coadd/*/*/*-invvar-<filter>.fits.fz). The order of the points within each file is also random (meaning that randomness is retained if just the first N rows of the file are read). Each file contains the following columns:

Column Type Description
RELEASE int16 Integer denoting the camera and filter set used, which will be unique for a given processing run of the data (RELEASE is documented here)
BRICKID int32 A unique Brick ID (in the range [1, 662174])
BRICKNAME char[8] Name of the brick
BRICK_OBJID int32 Random catalog object number enumerate by increasing RA within each brick; a unique identifier hash is RELEASE,BRICKID,BRICK_OBJID
RA float64 Right ascension at equinox J2000
DEC float64 Declination at equinox J2000
NOBS_G int16 Number of images that contribute to the central pixel in the \(g\) filter for this location (not profile-weighted)
NOBS_R int16 Number of images that contribute to the central pixel in the \(r\) filter for this location (not profile-weighted)
NOBS_Z int16 Number of images that contribute to the central pixel in the \(z\) filter for this location (not profile-weighted)
PSFDEPTH_G float32 For a \(5\sigma\) point source detection limit in \(g\), \(5/\sqrt(\mathrm{PSFDEPTH\_G})\) gives flux in nanomaggies and \(-2.5[\log_{10}(5 / \sqrt(\mathrm{PSFDEPTH\_G})) - 9]\) gives corresponding magnitude
PSFDEPTH_R float32 For a \(5\sigma\) point source detection limit in \(g\), \(5/\sqrt(\mathrm{PSFDEPTH\_R})\) gives flux in nanomaggies and \(-2.5[\log_{10}(5 / \sqrt(\mathrm{PSFDEPTH\_R})) - 9]\) gives corresponding magnitude
PSFDEPTH_Z float32 For a \(5\sigma\) point source detection limit in \(g\), \(5/\sqrt(\mathrm{PSFDEPTH\_Z})\) gives flux in nanomaggies and \(-2.5[\log_{10}(5 / \sqrt(\mathrm{PSFDEPTH\_Z})) - 9]\) gives corresponding magnitude
GALDEPTH_G float32 As for PSFDEPTH_G but for a galaxy (0.45" exp, round) detection sensitivity
GALDEPTH_R float32 As for PSFDEPTH_R but for a galaxy (0.45" exp, round) detection sensitivity
GALDEPTH_Z float32 As for PSFDEPTH_Z but for a galaxy (0.45" exp, round) detection sensitivity
PSFDEPTH_W1 float32 As for PSFDEPTH_G (and also on the AB system) but for WISE W1
PSFDEPTH_W2 float32 As for PSFDEPTH_G (and also on the AB system) but for WISE W2
PSFSIZE_G float32 Weighted average PSF FWHM in arcsec in the \(g\) band
PSFSIZE_R float32 Weighted average PSF FWHM in arcsec in the \(r\) band
PSFSIZE_Z float32 Weighted average PSF FWHM in arcsec in the \(z\) band
APFLUX_G float32 Total flux in nanomaggies extracted in a 0.75 arcsec radius in the \(g\) band at this location
APFLUX_R float32 Total flux in nanomaggies extracted in a 0.75 arcsec radius in the \(r\) band at this location
APFLUX_Z float32 Total flux in nanomaggies extracted in a 0.75 arcsec radius in the \(z\) band at this location
APFLUX_IVAR_G float32 Inverse variance of APFLUX_G
APFLUX_IVAR_R float32 Inverse variance of APFLUX_R
APFLUX_IVAR_Z float32 Inverse variance of APFLUX_Z
MASKBITS int16 Bitwise mask for optical data in the coadd/*/*/*maskbits* maps (see the DR9 bitmasks page)
WISEMASK_W1 uint8 Bitwise mask for WISE W1 data in the coadd/*/*/*maskbits* maps (see the DR9 bitmasks page)
WISEMASK_W2 uint8 Bitwise mask for WISE W2 data in the coadd/*/*/*maskbits* maps (see the DR9 bitmasks page)
EBV float32 Galactic extinction E(B-V) reddening from SFD98
PHOTSYS char[1] 'N' for an MzLS/BASS location, 'S' for a DECaLS location
HPXPIXEL int64 HEALPixel containing this location at NSIDE=64 in the NESTED scheme
TARGETID int64 See the desitarget data model (added to facilitate running randoms through the DESI fiberassign code)
DESI_TARGET int64 See the desitarget data model; set to 4, appropriate to a QSO, the highest-priority DESI dark-time target (added to facilitate running randoms through the DESI fiberassign code)
BGS_TARGET int64 See the desitarget data model; set to zero (added to facilitate running randoms through the DESI fiberassign code)
MWS_TARGET int64 See the desitarget data model; set to zero (added to facilitate running randoms through the DESI fiberassign code)
SUBPRIORITY int64 See the desitarget data model (added to facilitate running randoms through the DESI fiberassign code)
OBSCONDITIONS int32 See the desitarget data model; set to 511, which corresponds to all possible observing conditions (added to facilitate running randoms through the DESI fiberassign code)
PRIORITY_INIT int64 See the desitarget data model; set to 3400, appropriate to a QSO, the highest-priority DESI dark-time target (added to facilitate running randoms through the DESI fiberassign code)
NUMOBS_INIT int64 See the desitarget data model; set to 4, appropriate to a QSO, the highest-priority DESI dark-time target (added to facilitate running randoms through the DESI fiberassign code)
SCND_TARGET int64 See the desitarget data model; set to 0 (added to facilitate running randoms through the DESI fiberassign code)
NUMOBS_MORE int64 See the desitarget data model; set to 4, appropriate to a QSO, the highest-priority DESI dark-time target (added to facilitate running randoms through the DESI fiberassign code)
NUMOBS int64 See the desitarget data model; set to 0 (added to facilitate running randoms through the DESI fiberassign code)
Z float64 See the desitarget data model; set to -1.0 (added to facilitate running randoms through the DESI fiberassign code)
ZWARN int64 See the desitarget data model; set to -1 (added to facilitate running randoms through the DESI fiberassign code)
TARGET_STATE char[15] See the desitarget data model; set to "QSO|UNOBS", denoting an unobserved QSO (added to facilitate running randoms through the DESI fiberassign code)
TIMESTAMP char[19] See the desitarget data model; time at which this random was processed (added to facilitate running randoms through the DESI fiberassign code)
VERSION char[14] See the desitarget data model; version of the desitarget code used to process this random (added to facilitate running randoms through the DESI fiberassign code)
PRIORITY int64 See the desitarget data model; set to 3400, appropriate to a QSO, the highest-priority DESI dark-time target (added to facilitate running randoms through the DESI fiberassign code)

The version of the desitarget code used to generate the random catalogs (0.48.0) can be extracted from the VERSION column. The code is available on GitHub (see also here). The northern and southern imaging footprints overlap, so, randoms are resolved by the desitarget code at a particular declination and by the Galactic plane. The result is that randoms with locations at Dec \(\geq\) 32.375° and that are north of the Galactic Plane are only included in this file if they have pixels in BASS/MzLS (PHOTSYS set to "N"), and randoms with locations at Dec < 32.375° or that are south of the Galactic Plane are only included in this file if they have pixels in DECaLS (PHOTSYS set to "S").

randoms-outside-1-*.fits

Twenty files of random points in bricks that do not contain an observation in DR9 (that are "outside" of the DR9 footprint). The columns in this file are simplified compared to the other random catalogs as most of the entries in the additional columns would be zeros. As with the other random catalogs, points were generated at a density of 2,500 per square degree and the order of the points within the file is also randomized. Contains the following columns:

Column Type Description
BRICKID int32 A unique Brick ID (in the range [1, 662174])
BRICKNAME char[8] Name of the brick
RA float64 Right ascension at equinox J2000
DEC float64 Declination at equinox J2000
NOBS_G int16 Always zero in this file.
NOBS_R int16 Always zero in this file.
NOBS_Z int16 Always zero in this file.
EBV float32 Galactic extinction E(B-V) reddening from SFD98

randoms-allsky-1-*.fits

The (randomly shuffled) combination of each of the randoms-1-X.fits and randoms-outside-1-X.fits files (where X = 0, 1, 2, 3, ... 18, 19). This creates twenty "all-sky" random catalogs (at a density of 2,500 locations per square degree) where each brick is either populated with observations from the Legacy Surveys, or zeros. Contains a subset of the columns from the randoms-1-X.fits files.

survey-bricks-dr9-randoms-0.48.0.fits

A similar file to the survey-bricks.fits.gz file, but with extra columns to help interpret the random catalogs. Contains the same columns as the survey-bricks.fits.gz file, plus the additional columns:

Column Type Description
PHOTSYS char[1] "N", "S" or " " for bricks resolved to be "officially" in the north, south, or outside of the footprint, respectively.
AREA_PER_BRICK float64 The area of the brick in square degrees.

<region>/randoms/randoms-<region>-1-*.fits

As for the corresponding randoms-1-*.fits file, but for each <region> without resolving randoms using the desitarget code. In other words, this file contains all randoms for the northern (southern) imaging surveys, regardless of whether the brick is "officially" in the north (south) region.

External Match Files (<region>/external/*)

The Legacy Survey photometric catalogs have been matched to a range of external spectroscopic files from the SDSS. These external spectroscopic files can be accessed on the NERSC computers (for collaborators) at:
/global/cfs/cdirs/sdss/data/sdss
/global/cfs/cdirs/sdss/staging/dr16/sdss/spectro/redux/
The resulting catalogs, which are listed below, can be accessed through the web at:
https://portal.nersc.gov/cfs/cosmo/data/legacysurvey/dr9/north/external/
https://portal.nersc.gov/cfs/cosmo/data/legacysurvey/dr9/south/external/
Or on the NERSC computers at:
/global/cfs/cdirs/cosmo/data/legacysurvey/dr9/north/external/
/global/cfs/cdirs/cosmo/data/legacysurvey/dr9/south/external/

Each row of each external-match file contains the full record of the nearest object in our Tractored survey imaging catalogs, matched at a radius of 1.5 arcsec. The structure of the imaging catalog files is documented on the catalogs page. If no match is found, then OBJID is set to -1.

In addition to the columns from the Tractor catalogs, we have added columns from the SDSS files that can be used to track objects uniquely. These are typically some combination of PLATE, FIBER, MJD (or SMJD) and, in some cases, RERUN.

In previous Data Releases, if a source was duplicated in the SDSS spectroscopic files, only one of the duplicates was matched to a Legacy Surveys photometric object. Starting with DR9, we match all duplicates in the SDSS spectroscopic files. The result is that all sources in the SDSS spectroscopic files should have information from the Legacy Surveys imaging if they match with any Legacy Surveys BRICK_PRIMARY photometric object.

survey-dr9-<region>-specObj-dr16.fits

HDU1 (the only HDU) contains Tractored survey photometry that is row-by-row-matched to the SDSS DR16 spectrosopic pipeline file such that the photometric parameters in row "N" of survey-dr9-<region>-specObj-dr16.fits match the spectroscopic parameters in row "N" of specObj-dr16.fits. The spectroscopic file is documented in the SDSS DR16 data model for specObj-dr16.fits.

survey-dr9-<region>-dr16Q-v4.fits

HDU1 (the only HDU) contains Tractored survey photometry that is row-by-row-matched to the SDSS DR16 visually inspected quasar catalog (Lyke et al. 2020) such that the photometric parameters in row "N" of survey-dr9-<region>-dr16Q-v4.fits match the spectroscopic parameters in row "N" of DR16Q_v4.fits. The spectroscopic file is documented in the SDSS DR14 data model for DR16Q_v4.fits.

survey-dr9-<region>-superset-dr16Q-v3.fits

HDU1 (the only HDU) contains Tractored survey photometry that is row-by-row-matched to the superset of all SDSS DR16 spectroscopically confirmed objects that were visually inspected as possible quasars (Lyke et al. 2020) such that the photometric parameters in row "N" of survey-dr9-<region>-superset-dr16Q-v3.fits match the spectroscopic parameters in row "N" of DR16Q_Superset_v3.fits. The spectroscopic file is documented in the SDSS DR16 data model for DR16Q_Superset_v3.fits.

survey-dr9-<region>-dr12Q.fits

HDU1 (the only HDU) contains Tractored survey photometry that is row-by-row-matched to the SDSS DR12 visually inspected quasar catalog (Paris et al. 2017) such that the photometric parameters in row "N" of survey-dr9-<region>-dr12Q.fits match the spectroscopic parameters in row "N" of DR12Q.fits. The spectroscopic file is documented in the SDSS DR12 data model for DR12Q.fits.

survey-dr9-<region>-superset-dr12Q.fits

HDU1 (the only HDU) contains Tractored survey photometry that is row-by-row-matched to the superset of all SDSS DR12 spectroscopically confirmed objects that were visually inspected as possible quasars (Paris et al. 2017) such that the photometric parameters in row "N" of survey-dr9-<region>-superset-dr12Q.fits match the spectroscopic parameters in row "N" of Superset_DR12Q.fits. The spectroscopic file is documented in the SDSS DR12 data model for Superset_DR12Q.fits.

survey-dr9-<region>-dr7Q.fits

HDU1 (the only HDU) contains Tractored survey photometry that is row-by-row-matched to the SDSS DR7 visually inspected quasar catalog (Schneider et al. 2010) such that the photometric parameters in row "N" of survey-dr9-<region>-dr7Q.fits match the spectroscopic parameters in row "N" of DR7qso.fit. The spectroscopic file is documented on the DR7 quasar catalog description page.

Tractor Catalogs (<region>/tractor/*)

In the file listings outlined below:

  • brick names (<brick>) have the format <AAAa>c<BBB> where A, a and B are digits and c is either the letter m or p (e.g. 1126p222). The names are derived from the (RA, Dec) center of the brick. The first four digits are \(int(RA \times 10)\), followed by p to denote positive Dec or m to denote negative Dec ("plus"/"minus"), followed by three digits of \(int(Dec \times 10)\). For example the case 1126p222 corresponds to (RA, Dec) = (112.6°, +22.2°).
  • <brickmin> and <brickmax> denote the corners of a rectangle in (RA, Dec). Explicitly, <brickmin> has the format <AAA>c<BBB> where <AAA> denotes three digits of the minimum \(int(RA)\) in degrees, <BBB> denotes three digits of the minimum \(int(Dec)\) in degrees, and c uses the p/m ("plus"/"minus") format outlined in the previous bullet point. The convention is similar for <brickmax> and the maximum RA and Dec. For example 000m010-010m005 would correspond to a survey region limited by \(0^\circ \leq RA < 10^\circ\) and \(-10^\circ \leq Dec < -5^\circ\).
  • sub-directories are listed by the RA of the brick center, and sub-directory names (<AAA>) correspond to RA. For example 002 corresponds to brick centers between an RA of 2° and an RA of 3°.
  • <filter> denotes the \(g\), \(r\) or \(z\) band, using the corresponding letter.

Note that it is not possible to go from a brick name back to an exact (RA, Dec) center (the bricks are not on 0.1° grid lines). The exact brick center for a given brick name can be derived from columns in the survey-bricks.fits.gz file (i.e. brickname, ra, dec).

<AAA>/tractor-<brick>.fits

FITS binary table containing Tractor photometry, documented on the catalogs page.

Users interested in database access to the Tractor catalogs can contact the Astro Data Lab [2] at datalab@noao.edu.

Sweep Catalogs (<region>/sweep/*)

9.0/sweep-<brickmin>-<brickmax>.fits

The sweeps are light-weight FITS binary tables (containing a subset of the most commonly used Tractor measurements) of all the Tractor catalogs for which BRICK_PRIMARY==T in rectangles of RA, Dec.

Name Type Units Description
RELEASE int16   Integer denoting the camera and filter set used, which will be unique for a given processing run of the data (RELEASE is documented here)
BRICKID int32   A unique Brick ID (in the range [1, 662174])
BRICKNAME char[8]   Name of brick, encoding the brick sky position, eg "1126p222" near RA=112.6, Dec=+22.2
OBJID int32   Catalog object number within this brick; a unique identifier hash is RELEASE,BRICKID,OBJID; OBJID spans [0,N-1] and is contiguously enumerated within each blob
TYPE char[3]   Morphological model: "PSF"=stellar, "REX"="round exponential galaxy" = round EXP galaxy with a variable radius, "EXP"=exponential, "DEV"=deVauc, "SER"=Sersic, "DUP"==Gaia source fit by different model
RA float64 deg Right ascension at equinox J2000
DEC float64 deg Declination at equinox J2000
RA_IVAR float32 1/deg² Inverse variance of RA (no cosine term!), excluding astrometric calibration errors
DEC_IVAR float32 1/deg² Inverse variance of DEC, excluding astrometric calibration errors
DCHISQ float32[5]   Difference in χ² between successively more-complex model fits: PSF, REX, DEV, EXP, SER. The difference is versus no source.
EBV float32 mag Galactic extinction E(B-V) reddening from SFD98, used to compute MW_TRANSMISSION
FLUX_G float32 nanomaggies model flux in \(g\)
FLUX_R float32 nanomaggies model flux in \(r\)
FLUX_Z float32 nanomaggies model flux in \(z\)
FLUX_W1 float32 nanomaggies WISE model flux in \(W1\) (AB system)
FLUX_W2 float32 nanomaggies WISE model flux in \(W2\) (AB)
FLUX_W3 float32 nanomaggies WISE model flux in \(W3\) (AB)
FLUX_W4 float32 nanomaggies WISE model flux in \(W4\) (AB)
FLUX_IVAR_G float32 1/nanomaggies² Inverse variance of FLUX_G
FLUX_IVAR_R float32 1/nanomaggies² Inverse variance of FLUX_R
FLUX_IVAR_Z float32 1/nanomaggies² Inverse variance of FLUX_Z
FLUX_IVAR_W1 float32 1/nanomaggies² Inverse variance of FLUX_W1 (AB system)
FLUX_IVAR_W2 float32 1/nanomaggies² Inverse variance of FLUX_W2 (AB)
FLUX_IVAR_W3 float32 1/nanomaggies² Inverse variance of FLUX_W3 (AB)
FLUX_IVAR_W4 float32 1/nanomaggies² Inverse variance of FLUX_W4 (AB)
MW_TRANSMISSION_G float32   Galactic transmission in \(g\) filter in linear units [0,1]
MW_TRANSMISSION_R float32   Galactic transmission in \(r\) filter in linear units [0,1]
MW_TRANSMISSION_Z float32   Galactic transmission in \(z\) filter in linear units [0,1]
MW_TRANSMISSION_W1 float32   Galactic transmission in \(W1\) filter in linear units [0,1]
MW_TRANSMISSION_W2 float32   Galactic transmission in \(W2\) filter in linear units [0,1]
MW_TRANSMISSION_W3 float32   Galactic transmission in \(W3\) filter in linear units [0,1]
MW_TRANSMISSION_W4 float32   Galactic transmission in \(W4\) filter in linear units [0,1]
NOBS_G int16   Number of images that contribute to the central pixel in \(g\): filter for this object (not profile-weighted)
NOBS_R int16   Number of images that contribute to the central pixel in \(r\): filter for this object (not profile-weighted)
NOBS_Z int16   Number of images that contribute to the central pixel in \(z\): filter for this object (not profile-weighted)
NOBS_W1 int16   Number of images that contribute to the central pixel in \(W1\): filter for this object (not profile-weighted)
NOBS_W2 int16   Number of images that contribute to the central pixel in \(W2\): filter for this object (not profile-weighted)
NOBS_W3 int16   Number of images that contribute to the central pixel in \(W3\): filter for this object (not profile-weighted)
NOBS_W4 int16   Number of images that contribute to the central pixel in \(W4\): filter for this object (not profile-weighted)
RCHISQ_G float32   Profile-weighted χ² of model fit normalized by the number of pixels in \(g\)
RCHISQ_R float32   Profile-weighted χ² of model fit normalized by the number of pixels in \(r\)
RCHISQ_Z float32   Profile-weighted χ² of model fit normalized by the number of pixels in \(z\)
RCHISQ_W1 float32   Profile-weighted χ² of model fit normalized by the number of pixels in \(W1\)
RCHISQ_W2 float32   Profile-weighted χ² of model fit normalized by the number of pixels in \(W2\)
RCHISQ_W3 float32   Profile-weighted χ² of model fit normalized by the number of pixels in \(W3\)
RCHISQ_W4 float32   Profile-weighted χ² of model fit normalized by the number of pixels in \(W4\)
FRACFLUX_G float32   Profile-weighted fraction of the flux from other sources divided by the total flux in \(g\) (typically [0,1])
FRACFLUX_R float32   Profile-weighted fraction of the flux from other sources divided by the total flux in \(r\) (typically [0,1])
FRACFLUX_Z float32   Profile-weighted fraction of the flux from other sources divided by the total flux in \(z\) (typically [0,1])
FRACFLUX_W1 float32   Profile-weighted fraction of the flux from other sources divided by the total flux in \(W1\) (typically [0,1])
FRACFLUX_W2 float32   Profile-weighted fraction of the flux from other sources divided by the total flux in \(W2\) (typically [0,1])
FRACFLUX_W3 float32   Profile-weighted fraction of the flux from other sources divided by the total flux in \(W3\) (typically [0,1])
FRACFLUX_W4 float32   Profile-weighted fraction of the flux from other sources divided by the total flux in \(W4\) (typically [0,1])
FRACMASKED_G float32   Profile-weighted fraction of pixels masked from all observations of this object in \(g\), strictly between [0,1]
FRACMASKED_R float32   Profile-weighted fraction of pixels masked from all observations of this object in \(r\), strictly between [0,1]
FRACMASKED_Z float32   Profile-weighted fraction of pixels masked from all observations of this object in \(z\), strictly between [0,1]
FRACIN_G float32   Fraction of a source's flux within the blob in \(g\), near unity for real sources
FRACIN_R float32   Fraction of a source's flux within the blob in \(r\), near unity for real sources
FRACIN_Z float32   Fraction of a source's flux within the blob in \(z\), near unity for real sources
ANYMASK_G int16   Bitwise mask set if the central pixel from any image satisfies each condition in \(g\) (see the DR9 bitmasks page)
ANYMASK_R int16   Bitwise mask set if the central pixel from any image satisfies each condition in \(r\) (see the DR9 bitmasks page)
ANYMASK_Z int16   Bitwise mask set if the central pixel from any image satisfies each condition in \(z\) (see the DR9 bitmasks page)
ALLMASK_G int16   Bitwise mask set if the central pixel from all images satisfy each condition in \(g\) (see the DR9 bitmasks page)
ALLMASK_R int16   Bitwise mask set if the central pixel from all images satisfy each condition in \(r\) (see the DR9 bitmasks page)
ALLMASK_Z int16   Bitwise mask set if the central pixel from all images satisfy each condition in \(z\) (see the DR9 bitmasks page)
WISEMASK_W1 uint8   W1 bitmask as cataloged on the DR9 bitmasks page
WISEMASK_W2 uint8   W2 bitmask as cataloged on the DR9 bitmasks page
PSFSIZE_G float32 arcsec Weighted average PSF FWHM in the \(g\) band
PSFSIZE_R float32 arcsec Weighted average PSF FWHM in the \(r\) band
PSFSIZE_Z float32 arcsec Weighted average PSF FWHM in the \(z\) band
PSFDEPTH_G float32 1/nanomaggies² For a \(5\sigma\) point source detection limit in \(g\), \(5/\sqrt(\mathrm{PSFDEPTH\_G})\) gives flux in nanomaggies and \(-2.5[\log_{10}(5 / \sqrt(\mathrm{PSFDEPTH\_G})) - 9]\) gives corresponding magnitude
PSFDEPTH_R float32 1/nanomaggies² For a \(5\sigma\) point source detection limit in \(g\), \(5/\sqrt(\mathrm{PSFDEPTH\_R})\) gives flux in nanomaggies and \(-2.5[\log_{10}(5 / \sqrt(\mathrm{PSFDEPTH\_R})) - 9]\) gives corresponding magnitude
PSFDEPTH_Z float32 1/nanomaggies² For a \(5\sigma\) point source detection limit in \(g\), \(5/\sqrt(\mathrm{PSFDEPTH\_Z})\) gives flux in nanomaggies and \(-2.5[\log_{10}(5 / \sqrt(\mathrm{PSFDEPTH\_Z})) - 9]\) gives corresponding magnitude
GALDEPTH_G float32 1/nanomaggies² As for PSFDEPTH_G but for a galaxy (0.45" exp, round) detection sensitivity
GALDEPTH_R float32 1/nanomaggies² As for PSFDEPTH_R but for a galaxy (0.45" exp, round) detection sensitivity
GALDEPTH_Z float32 1/nanomaggies² As for PSFDEPTH_Z but for a galaxy (0.45" exp, round) detection sensitivity
PSFDEPTH_W1 float32 1/nanomaggies² As for PSFDEPTH_G (and also on the AB system) but for WISE W1
PSFDEPTH_W2 float32 1/nanomaggies² As for PSFDEPTH_G (and also on the AB system) but for WISE W2
WISE_COADD_ID char[8]   unWISE coadd file name for the center of each object
SHAPE_R float32 arcsec Half-light radius of galaxy model for galaxy type TYPE (>0)
SHAPE_R_IVAR float32 1/arcsec² Inverse variance of SHAPE_R
SHAPE_E1 float32   Ellipticity component 1 of galaxy model for galaxy type TYPE
SHAPE_E1_IVAR float32   Inverse variance of SHAPE_E1
SHAPE_E2 float32   Ellipticity component 2 of galaxy model for galaxy type TYPE
SHAPE_E2_IVAR float32   Inverse variance of SHAPE_E2
FIBERFLUX_G float32 nanomaggies Predicted \(g\)-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERFLUX_R float32 nanomaggies Predicted \(r\)-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERFLUX_Z float32 nanomaggies Predicted \(z\)-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERTOTFLUX_G float32 nanomaggies Predicted \(g\)-band flux within a fiber of diameter 1.5 arcsec from all sources at this location in 1 arcsec Gaussian seeing
FIBERTOTFLUX_R float32 nanomaggies Predicted \(r\)-band flux within a fiber of diameter 1.5 arcsec from all sources at this location in 1 arcsec Gaussian seeing
FIBERTOTFLUX_Z float32 nanomaggies Predicted \(z\)-band flux within a fiber of diameter 1.5 arcsec from all sources at this location in 1 arcsec Gaussian seeing
REF_CAT char[2]   Reference catalog source for this star: "T2" for Tycho-2, "G2" for Gaia DR2, "L3" for the SGA, empty otherwise
REF_ID int64   Reference catalog identifier for this star; Tyc1*1,000,000+Tyc2*10+Tyc3 for Tycho-2; "sourceid" for Gaia DR2 and SGA
REF_EPOCH float32 yr Reference catalog reference epoch (eg, 2015.5 for Gaia DR2)
GAIA_PHOT_G_MEAN_MAG float32 mag Gaia G band magnitude
GAIA_PHOT_G_MEAN_FLUX_OVER_ERROR float32   Gaia G band signal-to-noise
GAIA_PHOT_BP_MEAN_MAG float32 mag Gaia BP magnitude
GAIA_PHOT_BP_MEAN_FLUX_OVER_ERROR float32   Gaia BP signal-to-noise
GAIA_PHOT_RP_MEAN_MAG float32 mag Gaia RP magnitude
GAIA_PHOT_RP_MEAN_FLUX_OVER_ERROR float32   Gaia RP signal-to-noise
GAIA_ASTROMETRIC_EXCESS_NOISE float32   Gaia astrometric excess noise
GAIA_DUPLICATED_SOURCE boolean   Gaia duplicated source flag (1/0 for True/False)
GAIA_PHOT_BP_RP_EXCESS_FACTOR float32   Gaia BP/RP excess factor
GAIA_ASTROMETRIC_SIGMA5D_MAX float32 mas Gaia longest semi-major axis of the 5-d error ellipsoid
GAIA_ASTROMETRIC_PARAMS_SOLVED uint8   Which astrometric parameters were estimated for a Gaia source
PARALLAX float32 mas Reference catalog parallax
PARALLAX_IVAR float32 1/(mas)² Reference catalog inverse-variance on parallax
PMRA float32 mas/yr Reference catalog proper motion in the RA direction
PMRA_IVAR float32 1/(mas/yr)² Reference catalog inverse-variance on pmra
PMDEC float32 mas/yr Reference catalog proper motion in the Dec direction
PMDEC_IVAR float32 1/(mas/yr)² Reference catalog inverse-variance on pmdec
MASKBITS int16   Bitwise mask indicating that an object touches a pixel in the coadd/*/*/*maskbits* maps (see the DR9 bitmasks page)
FITBITS int16   Bitwise mask detailing properties of how a source was fit (see the DR9 bitmasks page)
SERSIC float32   Power-law index for the Sersic profile model (TYPE="SER")
SERSIC_IVAR float32   Inverse variance of SERSIC

Light Curve sweeps (9.0-lightcurves/sweep-<brickmin>-<brickmax>-lc.fits)

The "light curve" sweeps files contain values from the Tractor catalogs that relate to multi-epoch WISE data, which are

Name Type Units Description
RELEASE int16   Integer denoting the camera and filter set used, which will be unique for a given processing run of the data (RELEASE is documented here)
BRICKID int32   A unique Brick ID (in the range [1, 662174])
OBJID int32   Catalog object number within this brick; a unique identifier hash is RELEASE,BRICKID,OBJID; OBJID spans [0,N-1] and is contiguously enumerated within each blob
LC_FLUX_W1 float32[15] nanomaggies FLUX_W1 in each of up to fifteen unWISE coadd epochs (AB system; defaults to zero for unused entries)
LC_FLUX_W2 float32[15] nanomaggies FLUX_W2 in each of up to fifteen unWISE coadd epochs (AB; defaults to zero for unused entries)
LC_FLUX_IVAR_W1 float32[15] 1/nanomaggies² Inverse variance of LC_FLUX_W1 (AB system; defaults to zero for unused entries)
LC_FLUX_IVAR_W2 float32[15] 1/nanomaggies² Inverse variance of LC_FLUX_W2 (AB; defaults to zero for unused entries)
LC_NOBS_W1 int16[15]   NOBS_W1 in each of up to fifteen unWISE coadd epochs
LC_NOBS_W2 int16[15]   NOBS_W2 in each of up to fifteen unWISE coadd epochs
LC_MJD_W1 float64[15]   MJD_W1 in each of up to fifteen unWISE coadd epochs (defaults to zero for unused entries)
LC_MJD_W2 float64[15]   MJD_W2 in each of up to fifteen unWISE coadd epochs (defaults to zero for unused entries)
LC_FRACFLUX_W1 float32[15]   FRACFLUX_W1 in each of up to fifteen unWISE coadd epochs (defaults to zero for unused entries)
LC_FRACFLUX_W2 float32[15]   FRACFLUX_W2 in each of up to fifteen unWISE coadd epochs (defaults to zero for unused entries)
LC_RCHISQ_W1 float32[15]   RCHISQ_W1 in each of up to fifteen unWISE coadd epochs (defaults to zero for unused entries)
LC_RCHISQ_W2 float32[15]   RCHISQ_W2 in each of up to fifteen unWISE coadd epochs (defaults to zero for unused entries)
LC_EPOCH_INDEX_W1 int16[15]   Index number of unWISE epoch for W1 (defaults to -1 for unused entries)
LC_EPOCH_INDEX_W2 int16[15]   Index number of unWISE epoch for W2 (defaults to -1 for unused entries)

The light curve sweeps files are row-by-row-parallel to the standard sweeps files (i.e. the entries in each row of the light curve sweeps files correspond to the entries in each row of the standard sweeps files, which can be verified using RELEASE, BRICKID and OBJID).

Extra sweeps (9.0-lightcurves/sweep-<brickmin>-<brickmax>-ex.fits)

The "extra" sweeps files contain all columns from the Tractor catalogs that are not otherwise in the standard sweeps files or the "light curve" sweep files. See the Tractor catalogs for a description of the columns in these files. The extra sweeps files are row-by-row-parallel to the standard sweeps files (i.e. the entries in each row of the extra sweeps files correspond to the entries in each row of the standard sweeps files, which can be verified using RELEASE, BRICKID and OBJID).

Photometric Redshift sweeps

The Photometric Redshifts for the Legacy Surveys (PRLS, e.g., see Zhou et al. 2021) catalog is row-by-row-matched to the DR9 sweep catalogs as described previously for the other types of sweeps files.

The photometric redshifts are computed using the random forest algorithm. Details of the photo-z training and performance can be found in Zhou et al. (2021). For computing the photo-z's, we require at least one exposure in \(g\), \(r\) and \(z\) bands (NOBS_G,R,Z>1). For objects that do not meet the NOBS cut, the photo-z values are filled with -99. Although we provide photo-z's for all objects that meet the NOBS cut, only relatively bright objects have reliable photo-z's. As a rule of thumb, objects brighter than \(z\)-band magnitude of 21 are mostly reliable, whereas fainter objects are increasingly unreliable with large systematic offsets.

The photo-z catalogs do not provide information on star-galaxy separation. Stars are excluded from the photo-z training data, and we do not attempt to identify stars. To perform star-galaxy separation, one can use the morphological "TYPE" and/or the photometry (e.g., the optical-WISE color cut, as applied in Zhou et al. 2021, can be very effective for selecting redshift ≳ 0.3 galaxies) in the sweep catalogs.

Name Type Description
RELEASE int16 Integer denoting the camera and filter set used, which will be unique for a given processing run of the data (RELEASE is documented here)
BRICKID int32 A unique Brick ID (in the range [1, 662174])
OBJID int32 Catalog object number within this brick; a unique identifier hash is RELEASE,BRICKID,OBJID; OBJID spans [0,N-1] and is contiguously enumerated within each blob
Z_PHOT_MEAN float32 photo-z derived from the mean of the photo-z PDF
Z_PHOT_MEDIAN float32 photo-z derived from the median of the photo-z PDF
Z_PHOT_STD float32 standard deviation of the photo-z's derived from the photo-z PDF
Z_PHOT_L68 float32 lower bound of the 68% confidence region, derived from the photo-z PDF
Z_PHOT_U68 float32 upper bound of the 68% confidence region, derived from the photo-z PDF
Z_PHOT_L95 float32 lower bound of the 95% confidence region, derived from the photo-z PDF
Z_PHOT_U95 float32 upper bound of the 68% confidence region, derived from the photo-z PDF
Z_SPEC float32 spectroscopic redshift, if available
SURVEY char[10] source of the spectroscopic redshift
TRAINING boolean whether or not the spectroscopic redshift is used in photometric redshift training

Work which uses this photometric redshift catalog should cite Zhou et al. (2021) and include the additional acknowledgment for photometric redshifts.

Foreground object masks (masking/*)

The foreground object masks were used to set the BRIGHT, MEDIUM, GALAXY and CLUSTER bits described on the DR9 bitmasks page. Files in the masking directory other than gaia-mask-dr9.fits.gz are generally described as part the overview of the external catalogs used for masking, and have data models that are detailed as part of the Siena Galaxy Atlas (SGA).

gaia-mask-dr9.fits.gz

A FITS binary table with a single HDU containing information about the Tycho-2 and Gaia DR2 stars used to set the BRIGHT and MEDIUM bits described on the DR9 bitmasks page. See also the general overview of the external catalogs used for masking.

Name Type Units Description
ra float64 deg Right ascension from the Gaia DR2 or Tycho-2 catalog
dec float64 deg Declination from the Gaia DR2 or Tycho-2 catalog
ref_cat char[2]   Reference catalog source for this star: "T2" for Tycho-2, "G2" for Gaia DR2
ref_id int64   Reference catalog identifier for this star; Tyc1*1,000,000+Tyc2*10+Tyc3 for Tycho-2; "sourceid" for Gaia DR2
ref_epoch float32 yr Reference catalog reference epoch (eg, 2015.5 for Gaia DR2)
mag float32 mag Gaia G-band mag for Gaia DR2; V_T for Tycho-2 when available, otherwise Hipparcos magnitude
mask_mag float32 mag Magnitude used for masking: the lesser of mag or (zguess + 1)
radius float32 deg Masking radius
radius_pix int64 pix Masking radius in 0.262 arcsec "brick" pixels
pmra float32 mas/yr Reference catalog proper motion in the RA direction
pmdec float32 mas/yr Reference catalog proper motion in the Dec direction
parallax float32 mas Reference catalog parallax
ra_ivar float32 1/deg² Inverse variance of RA (no cosine term!), excluding astrometric calibration errors
dec_ivar float32 1/deg² Inverse variance of DEC, excluding astrometric calibration errors
pmra_ivar float32 1/(mas/yr)² Reference catalog inverse-variance on pmra
pmdec_ivar float32 1/(mas/yr)² Reference catalog inverse-variance on pmdec
parallax_ivar float32 1/(mas)² Reference catalog inverse-variance on parallax
in_desi boolean   In the DESI footprint?
istycho boolean   From, or was matched to, the Tycho-2 catalog?
isgaia boolean   From, or was matched to, the Gaia DR2 catalog?
isbright boolean   Is a BRIGHT star? BRIGHT stars are all Tycho-2 stars, plus Gaia DR2 stars with mask_mag < 13 (see also the DR9 bitmasks page)
ismedium boolean   Is a MEDIUM star? MEDIUM stars are Gaia DR2 stars with mask_mag < 16 (see also the DR9 bitmasks page)
pointsource boolean   Does the star pass the Legacy Surveys Gaia DR2 point source cut?
donotfit boolean   Does the object match an SGA galaxy? If True then the object will appear in the Tractor catalogs as a "DUP" source.
decam_mag_g float32 mag The estimated DECam \(g\) magnitude for Gaia DR2 stars based on the \(G\) and \(Bp-Rp\) color
decam_mag_r float32 mag The estimated DECam \(r\) magnitude for Gaia DR2 stars based on the \(G\) and \(Bp-Rp\) color
decam_mag_z float32 mag The estimated DECam \(z\) magnitude for Gaia DR2 stars based on the \(G\) and \(Bp-Rp\) color
zguess float32 mag The estimated \(z\) magnitude for Tycho-2 stars from matching to 2MASS and estimating \(V\) to \(z\) transformations based on APASS.
brickname char[8]   Name of brick, encoding the brick sky position, eg "1126p222" near RA=112.6, Dec=+22.2
ibx int32   Integer brick pixel X coordinate (0-indexed) of this star
iby int32   Integer brick pixel Y coordinate (0-indexed) of this star
gaia_phot_g_mean_mag float32 mag Gaia G band magnitude
gaia_phot_g_mean_flux_over_error float32   Gaia G band signal-to-noise
gaia_phot_g_n_obs int16   Gaia G band number of observations
gaia_phot_bp_mean_mag float32 mag Gaia BP magnitude
gaia_phot_bp_mean_flux_over_error float32   Gaia BP signal-to-noise
gaia_phot_bp_n_obs int16   Gaia BP number of observations
gaia_phot_rp_mean_mag float32 mag Gaia RP magnitude
gaia_phot_rp_mean_flux_over_error float32   Gaia RP signal-to-noise
gaia_phot_rp_n_obs int16   Gaia RP number of observations
gaia_phot_variable_flag boolean   Gaia photometric variable flag
gaia_astrometric_excess_noise float32   Gaia astrometric excess noise
gaia_astrometric_excess_noise_sig float32   Gaia astrometric excess noise uncertainty
gaia_astrometric_n_obs_al int16   Gaia number of astrometric observations along scan direction
gaia_astrometric_n_good_obs_al int16   Gaia number of good astrometric observations along scan direction
gaia_astrometric_weight_al float32   Gaia astrometric weight along scan direction
gaia_duplicated_source boolean   Gaia duplicated source flag
gaia_a_g_val float32 mag Gaia line-of-sight extinction in the G band
gaia_e_bp_min_rp_val float32 mag Gaia line-of-sight reddening E(BP-RP)
gaia_phot_bp_rp_excess_factor float32   Gaia BP/RP excess factor
gaia_astrometric_sigma5d_max float32 mas Gaia longest semi-major axis of the 5-d error ellipsoid
gaia_astrometric_params_solved uint8   which astrometric parameters were estimated for a Gaia source

Image Stacks (<region>/coadd/*)

Image stacks are on tangent-plane (WCS TAN) projections, 3600 × 3600 pixels, at 0.262 arcseconds per pixel.

  • <AAA>/<brick>/legacysurvey-<brick>-blobmodel-<filter>.fits.fz

    The Tractor's model prediction of the images, similar to <AAA>/<brick>/legacysurvey-<brick>-model-<filter>.fits.fz, below, except that the models are clipped to the blobs within which they are measured. In other words, the models used to derive the maps in these files are not extrapolated beyond the pixels in the blobs that are used to fit the models.

  • <AAA>/<brick>/legacysurvey-<brick>-ccds.fits

    FITS binary table with the list of CCD images that were used in this brick. Contains the same columns as survey-ccds-<camera>-dr9.fits.gz, and also contains the additional columns listed below. Note that string columns can have different lengths in the survey-ccds-<camera>-dr9.fits.gz and legacysurvey-<brick>-ccds.fits files and can differ for <region> equal to <north> and <south>. For example the camera column can change from char[7] to char[5] (see, e.g. legacypipe issue #379).

    Column Type Description
    ccd_x0 int16 Minimum x image coordinate overlapping this brick
    ccd_y0 int16 Minimum y image coordinate overlapping this brick
    ccd_x1 int16 Maximum x image coordinate overlapping this brick
    ccd_y1 int16 Maximum y image coordinate overlapping this brick
    brick_x0 int16 Minimum x brick image coordinate overlapped by this image
    brick_x1 int16 Maximum x brick image coordinate overlapped by this image
    brick_y0 int16 Minimum y brick image coordinate overlapped by this image
    brick_y1 int16 Maximum y brick image coordinate overlapped by this image
    psfnorm float32 Same as psfnorm in the ccds-annotated- file
    galnorm float32 Same as galnorm in the ccds-annotated- file
    skyver char[8] Git version of the sky calibration code
    wcsver char[1] Git version of the WCS calibration code
    psfver char[7] Git version of the PSF calibration code
    skyplver char[8] Community Pipeline (CP) version of the input to sky calibration
    wcsplver char[5] CP version of the input to WCS calibration
    psfplver char[8] CP version of the input to PSF calibration
    co_sky float32  
  • <AAA>/<brick>/legacysurvey-<brick>-chi2-<filter>.fits.fz
    Stacked χ² image, which is approximately the summed χ² values from the single-epoch images.
  • <AAA>/<brick>/legacysurvey-<brick>-depth-<filter>.fits.fz
    Stacked depth map in units of the point-source flux inverse-variance at each pixel.
    • The 5σ point-source depth can be computed as \(5 / \sqrt(\mathrm{depth\_ivar})\) .
  • <AAA>/<brick>/legacysurvey-<brick>-galdepth-<filter>.fits.fz
    Stacked depth map in units of the canonical galaxy flux inverse-variance at each pixel. The canonical galaxy is an exponential profile with effective radius 0.45" and round shape.
    • The 5σ galaxy depth can be computed as \(5 / \sqrt(\mathrm{galdepth\_ivar})\) .
  • <AAA>/<brick>/legacysurvey-<brick>-image-<filter>.fits.fz
    Stacked image centered on a brick location covering 0.25° × 0.25°. The primary HDU contains the coadded image (inverse-variance weighted coadd), in units of nanomaggies per pixel.
    • NOTE: These are not the images used by Tractor, which operates on the single-epoch images.
    • NOTE: These images are resampled using Lanczos-3 resampling.
    • NOTE: Images in WISE bands are on the Vega system, all other flux-related quantities in DR9 are reported on the AB system. The description page lists the Vega-to-AB conversions recommended by the WISE team.
  • <AAA>/<brick>/legacysurvey-<brick>-invvar-<filter>.fits.fz
    Inverse variance image corresponding to the legacysurvey-<brick>-image-<filter>.fits.fz file based on the sum of the inverse-variances of the individual input images in units of 1/(nanomaggies)² per pixel.
    • NOTE: These are not the inverse variance maps used by Tractor, which operates on the single-epoch images.
    • NOTE: Images in WISE bands are on the Vega system, all other flux-related quantities in DR9 are reported on the AB system. The description page lists the Vega-to-AB conversions recommended by the WISE team.
  • <AAA>/<brick>/legacysurvey-<brick>-maskbits.fits.fz
    Bitmask of possible problems with pixels in this brick.
  • <AAA>/<brick>/legacysurvey-<brick>-model-<filter>.fits.fz
    Stacked model image centered on a brick location covering 0.25° × 0.25°.
    • The Tractor's idea of what the coadded images should look like; the Tractor's model prediction.
    • NOTE: Images in WISE bands are on the Vega system, all other flux-related quantities in DR9 are reported on the AB system. The description page lists the Vega-to-AB conversions recommended by the WISE team.
  • <AAA>/<brick>/legacysurvey-<brick>-nexp-<filter>.fits.fz
    Number of exposures contributing to each pixel of the stacked images.
  • <AAA>/<brick>/legacysurvey-<brick>-psfsize-<filter>.fits.fz
    Weighted average PSF FWHM in arcsec at each pixel of the stacked images.
  • <AAA>/<brick>/legacysurvey-<brick>-blobmodel.jpg
    JPEG image of the Tractor's model images, where the model fits have been clipped to the blobs within which the models are measured. Uses the \(g,r,z\) filters as the colors.
  • <AAA>/<brick>/legacysurvey-<brick>-image.jpg
    JPEG image of the calibrated image using the \(g,r,z\) filters as the colors.
  • <AAA>/<brick>/legacysurvey-<brick>-model.jpg
    JPEG image of the Tractor's model image using the \(g,r,z\) filters as the colors.
  • <AAA>/<brick>/legacysurvey-<brick>-resid.jpg
    JPEG image of the residual image (data minus model) using the \(g,r,z\) filters as the colors.
  • <AAA>/<brick>/legacysurvey-<brick>-wise.jpg
    JPEG image of the calibrated image using the WISE filters as the colors.
  • <AAA>/<brick>/legacysurvey-<brick>-wisemodel.jpg
    JPEG image of the model image using the WISE filters as the colors.

Forced Photometry Files (forced/*)

Files in this directory contain forced photometry results, for all CCDs that were included in the DR9 processing.

That is, after we produce the catalogs based on fitting to all images simultaneously, we go back to the individual CCDs, select the catalog objects that overlap, and ask what fluxes those objects should have to best match what is observed in the CCD. When selecting objects from the catalog, we resolve the north and south components using the same cut as in the sweep files and randoms.

We perform two fits. The first is regular forced photometry, where the position and profile of the sources are fixed, and all we are fitting is the flux. In the second fit, we compute the source-centered spatial derivatives and fit the amplitudes of those derivatives as well. For sources moving less than a pixel or two, this produces an approximate estimate of the motion of the source (dra and ddec). Note that for Gaia sources, this is relative to the Gaia measured proper motion!

  • forced/<camera>/<EXPOS>/forced-<camera>-<EXPOSURE>.fits

    Where <camera> is one of 90prime for BASS, decam for DECaLS or mosaic for MzLS, <EXPOSURE> is the exposure number (not necessarily as an 8-character string, unlike some other data products), and <EXPOS> is the first 5 characters of the exposure number printed as an 8-character string.

    This file contains a single FITS binary table for all the CCDs in this exposure, contatenated into one long table.

    For the columns pertaining to the catalog objects, see the catalog description page.

    Column Type Description
    release int16 Integer denoting the camera and filter set used, which will be unique for a given processing run of the data (release is documented here)
    brickid int32 Unique Brick ID (in the range [1, 662174]) that the catalog object came from
    brickname char[8] Name of brick, encoding the brick sky position, eg "1126p222" near RA=112.6, Dec=+22.2, of the catalog object
    objid int32 Catalog object number within this brick; a unique identifier hash is release,brickid,objid
    camera char[7] The camera for the CCD being measured, eg "decam"
    expnum int64 The exposure number of the CCD being measured, eg 574299
    ccdname char[4] The name of the CCD being measured, eg "N10" or "CCD4"
    filter char[1] The filter of the CCD being measured ("g", "r" or "z")
    mjd float64 The Modified Julian Date when the exposure was taken, in UTC, eg 57644.31537588
    exptime float32 The exposure time in seconds, eg 90.0
    psfsize float32 PSF FWHM in this exposure, in arcsec
    ccd_cuts int64 Bit mask describing CCD image quality (see the DR9 bitmasks page)
    airmass float32 Airmass of this observation
    sky float32 Sky background surface brightness, in nanomaggies/arcsec²
    psfdepth float32 Inverse-variance for the flux measured from a point source; for a \(5\sigma\) point source detection limit use \(5/\sqrt(\mathrm{psfdepth})\) for the flux in nanomaggies and \(-2.5[\log_{10}(5 / \sqrt(\mathrm{psfdepth})) - 9]\) for the corresponding AB magnitude
    galdepth float32 Inverse-variance for the flux measured from a nominal galaxy source (0.45" round exponential galaxy)
    ra float64 Right Ascension in degrees
    dec float64 Declination in degrees
    flux float32 Measured flux for this catalog object in this CCD, in nanomaggies
    flux_ivar float32 Inverse-variance of the flux measurement, in 1/nanomaggies²
    fracflux float32 Profile-weighted fraction of the flux from other sources over total flux
    rchisq float32 Profile-weighted χ² residual chi-squared per pixel
    fracmasked float32 Profile-weighted fraction of pixels masked
    apflux float32[8] Aperture fluxes in this CCD, in nanomaggies, for aperture radii [0.5, 0.75, 1.0, 1.5, 2.0, 3.5, 5.0, 7.0] arcsec
    apflux_ivar float32[8] Inverse-variance on apflux, in 1/nanomaggies²
    x float32 Horizontal pixel position of the catalog source in this CCD, in zero-indexed pixels
    y float32 Vertical pixel position of the catalog source in this CCD, in zero-indexed pixels
    dqmask int16 Data Quality mask from the CP pipeline for the center pixel (defined as for ALLMASK/ANYMASK on the DR9 bitmasks page)
    dra float32 When fitting for spatial derivatives, the motion of the source in the RA direction, in arcsec
    ddec float32 Motion of the source in the Dec direction, in arcsec
    dra_ivar float32 Inverse-variance on dra, in 1/arcsec|sup2|
    ddec_ivar float32 Inverse-variance on ddec, in 1/arcsec|sup2|

Other Files

Much additional information is available as part of the DESI Legacy Imaging Surveys Data Releases, including, in separate directories, statistics of the Tractor fits (<region>/metrics), code outputs from the fitting processes (<region>/logs) and additional files detailing the calibrations (calib). We don't expect that most users will need a description of these files, but contact us if you require more information.

Raw Data

Astro Data Lab access to raw and calibrated images will be available a few weeks after the DR9 release date, at which point this documentation could be updated.

Raw and Calibrated Legacy Survey images are available from the Astro Data Lab's Science Archive through the web portal (http://archive.noao.edu/search/query) and an ftp server. The input data used to create the stacked images, Tractor catalogs, etc. comprise images taken by the dedicated DESI Legacy Imaging Surveys project, as well as other images from the NOIRLab telescopes.

(i) Web interface

  1. Query the Astro Data Lab's Science Archive.
  2. From the menu of "Available Collections" on the left, select the desired data release (e.g. LS-DR9).
  3. Under "Data products - Raw data" check "Object".
  4. Optionally, you may select data from specific filters, or restrict the search by other parameters such as sky coordinates, observing date, or exposure time.
  5. Click "Search".
  6. The Results page offers several different ways to download the data. See the Tutorials page for details.

(ii) ftp sites

Following the organization of the Stacked images, Raw and Calibrated images are organized by survey brick, which are defined in the file survey-bricks-dr9.fits.gz for DR9. Both the main Tractor catalogs and Sweep catalogs include the BRICKNAME keyword (corresponding to <brick> with format <AAAa>c<BBB>).

For the calibrated images, filenames can be retrieved from the IMAGE_FILENAME keyword in each brick from legacysurvey-<brick>-ccds.fits. Additionally, each calibrated/<AAA>/<brick> contains an ASCII file with a list of EXPID and IMAGE_FILENAME (legacysurvey-<brick>-image_filename.txt). EXPID contains the exposure number and the CCD name with the format EXPNUM-ccd. There is one entry per CCD. Often, multiple CCDs from a given file are used so there are fewer unique filenames than the number of CCDs. Each legacysurvey-<brick>-image_filename.txt file contains the number of unique images in the last row (File Count).

Note that the weight map images (the oow files) are in the same units as \(1/\mathtt{skyrms}^2\) in the survey-ccds-<camera>-dr9.fits.gz files (documented above). But, these images need to be multiplied by both gain and exptime to retrieve units of electrons (for <camera> of mosaic or 90prime).


Footnotes

[1] The cosky_x (where x \(= g, r\) or \(z\)) level is subtracted from each individual exposure (and hence also from the coadd) for the corresponding filter.
[2] The Astro Data Lab is part of the Community Science and Data Center (CSDC) of NSF's National Optical Infrared Astronomy Research Laboratory.