Legacy Survey Files

Top level directory for web access:
http://portal.nersc.gov/project/cosmo/data/legacysurvey/dr4/
Top level directory local to NERSC computers (for collaborators):
/global/project/projectdirs/cosmo/data/legacysurvey/dr4/

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 DR4. For that information, see the next file description.

  • HDU1 (only HDU) - tags in the survey-bricks.fits.gz file
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.

survey-bricks-dr4.fits.gz

A FITS binary table with information that summarizes the contents of each brick for DR4.

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_UNIQUE objects in this brick, of all types
npsf int16 Total number of BRICK_UNIQUE objects in this brick, of type PSF
nsimp int16 Total number of BRICK_UNIQUE objects in this brick, of type SIMP
nexp int16 Total number of BRICK_UNIQUE objects in this brick, of type EXP
ndev int16 Total number of BRICK_UNIQUE objects in this brick, of type DEV
ncomp int16 Total number of BRICK_UNIQUE objects in this brick, of type COMP
psfsize_g float32 Median PSF size, in arcsec, evaluated at the BRICK_UNIQUE objects in this brick in g-band
psfsize_r float32 Median PSF size, in arcsec, evaluated at the BRICK_UNIQUE objects in this brick in r-band
psfsize_z float32 Median PSF size, in arcsec, evaluated at the BRICK_UNIQUE 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 SFD dust map E(B-V) extinction, in magnitudes, evaluated at BRICK_UNIQUE 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
ext_g float32 Extinction (calculated, for DR4, assuming BASS and MzLS are on the DECam filter system) in \(g\)-band
ext_r float32 Extinction (calculated, for DR4, assuming BASS and MzLS are on the DECam filter system) in \(r\)-band
ext_z float32 Extinction (calculated, for DR4, assuming BASS and MzLS are on the DECam filter system) 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

Note that, for the nexphist rows, pixels that are masked by the NOAO Community Pipeline as, e.g., cosmic rays or saturation, 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-bass.fits.gz and survey-ccds-mzls.fits.gz

FITS binary tables with almanac information (e.g. seeing, etc.) about each individual CCD image for BASS and MzLS, respectively.

These files contain information regarding the photometric and astrometric zero points for each CCD of every Legacy Survey image that is part of DR4. Photometric zero points for each CCD are computed by identifying stars and comparing their instrumental magnitudes (measured in an approximately 7 arcsec diameter aperture) to color-selected stars in Pan-STARRS, as outlined further on the description page.

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 \(30 * 10^{((25.04 - 22.5) / 2.5)} = 311.3\) counts.

Column Type Description
object char[24] Name listed in the object tag from the CCD header
expnum int32 Exposure number, eg 348224
exptime float32 Exposure time in seconds, eg 30
filter char[1] Filter used for observation, eg "\(g\)", "\(r\)", "\(z\)"
seeing float32 Seeing in arcseconds determined by fitting a 2-dimensional gaussian to the median PSF of stars on the CCD, eg 1.1019
date_obs char[10] Date of observation start, eg "2014-08-15". Can be combined with ut, or use mjd_obs instead
mjd_obs float64 Date of observation in MJD (in UTC system), eg 56884.99373389
ut char[12] Time of observation start, eg "23:50:58.608241"
ha char[12] Hour angle of the observation (HH:MM:SS)
airmass float32 Airmass, eg 1.35
propid char[12] NOAO Proposal ID that took this image, eg "2014B-0404"
zpt float32 Median zero point for the entire image (median of all CCDs of the image), eg 25.0927
avsky float32 Average sky level in this image, in ADU, eg 36.9324. avsky is detailed more here
arawgain float32 Average gain for this CCD, eg 4.34
fwhm float32 (use "seeing" instead)
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
ccdnum int16 CCD number (see Legacy Survey camera layout), eg 1
ccdname char[4] CCD name (see Legacy Survey camera layout), eg "N10", "S7"
ccdzpt float32 Zeropoint for the CCD (AB mag)
ccdzpta float32 Zeropoint for amp A (AB mag)
ccdzptb float32 Zeropoint for amp B (AB mag)
ccdzptc float32 Zeropoint for amp C (AB mag)
ccdzptd float32 Zeropoint for amp D (AB mag)
ccdphoff float32 (ignore; depends on the nominal zeropoint, measured at the start of each survey rather than now)
ccdphrms float32 Photometric rms for the CCD (in mag)
ccdskyrms float32 Sky rms (in counts)
ccdskymag float32 Mean sky background in AB mag/arcsec2 on each CCD; measured from the CP-processed frames as -2.5*alog10(ccdskycounts/pixscale/pixscale/exptime) + ccdzpt
ccdskycounts float32 Mean sky count level per pixel in the CP-processed frames measured (with iterative rejection) for each CCD in the image section [500:1500,1500:2500]
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
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
ccdtransp float32 (ignore; depends on the nominal zeropoint, measured at the the start of survey rather than now)
ccdnstar int16 Number of stars found on the CCD
ccdnmatch int16 Number of stars matched to Pan-STARRS (and used to compute the photometric zero points)
ccdnmatcha int16 Number of stars in amp A matched
ccdnmatchb int16 Number of stars in amp B matched
ccdnmatchc int16 Number of stars in amp C matched
ccdnmatchd int16 Number of stars in amp D matched
ccdmdncol float32 Median (g-i) color from the PS1 catalog of the matched stars
psfab float32 (ignore)
psfpa float32 (ignore)
temp float32 Outside temperature in oC listed in the OUTTEMP tag in the CCD image header
badimg int16 (ignore)
camera char[7] The camera that took this image
expid char[15] Exposure ID string, eg "00348224-S29" (from expnum and ccdname)
image_hdu int16 FITS HDU number in the image_filename file where this image can be found
image_filename char[55] Path to FITS image, eg "decam/CP20140810_g_v2/c4d_140815_235218_ooi_g_v2.fits.fz"
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)
ra float64 Approximate RA center of this CCD (deg)
dec float64 Approximate Dec center of this CCD (deg)
photometric boolean True if this CCD was considered photometric and used in the DR4 reductions
bitmask uint8 bitmask is documented here
telfocus float32[3] (ignore)

ccds-annotated-dr4-90prime.fits.gz and ccds-annotated-dr4-mzls.fits.gz

Versions of the survey-ccds* files for BASS and MzLS, respectively. These files contain additional information gathered during calibration pre-processing before running the Tractor reductions.

Includes everything listed in the survey-ccds* files plus the following:

Column Type Description
ccd_cuts int32 (ignore)
annotated boolean (ignore)
good_region int16 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
sig1 float32 Median per-pixel error standard deviation, in nanomaggies.
meansky float32 Our pipeline (not the CP) estimate of the sky level, average over the image, in ADU.
stdsky float32 Standard deviation of our sky level
maxsky float32 Max of our sky level
minsky float32 Min of our sky level
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
psf_sampling float32 (ignore)
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 SFD E(B-V) extinction in the tile, 0 for data from programs other than BASS, MzLS or DECaLS
plver char[6] Community Pipeline (CP) PLVER version string
ebv float32 SFD 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

dr4-depth.fits.gz

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

dr4-depth-summary.fits.gz

A summary of the depth histogram of the whole DR4 survey. 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 goes 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.

External Files

The Legacy Survey photometric catalogs have been matched to the following external spectroscopic files from the SDSS, which can be accessed through the web at:
http://portal.nersc.gov/project/cosmo/data/legacysurvey/dr4/external/
Or on the NERSC computers (for collaborators) at:
/global/project/projectdirs/cosmo/data/legacysurvey/dr4/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 1.0 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.

survey-dr4-specObj-dr13.fits

HDU1 (the only HDU) contains Tractored survey photometry that is row-by-row-matched to the SDSS DR13 spectrosopic pipeline file such that the photometric parameters in row "N" of survey-dr4-specObj-dr13.fits matches the spectroscopic parameters in row "N" of specObj-dr13.fits. The spectroscopic file is documented in the SDSS DR13 data model for specObj-dr13.fits.

survey-dr4-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. 2016) such that the photometric parameters in row "N" of survey-dr4-DR12Q.fits matches the spectroscopic parameters in row "N" of DR12Q.fits. The spectroscopic file is documented in the SDSS DR12 data model for DR12Q.fits.

survey-dr4-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-dr4-Superset_DR12Q.fits matches 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-dr4-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-dr4-DR7Q.fits matches the spectroscopic parameters in row "N" of DR7qso.fit. The spectroscopic file is documented on the DR7 quasar catalog description page.

Tractor Catalogs

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 \(int(RA * 10)\), followed by p to denote positive Dec or m to denote negative Dec ("plus"/"minus"), followed by three digits of \(int(Dec * 10)\). 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 using the format outlined in the previous bullet point. 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).

tractor/<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 NOAO Data Lab at datalab@noao.edu.

Sweep Catalogs

sweep/4.0/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. Includes:

Name Type Units Description
RELEASE int32   Unique integer denoting the camera and filter set used (RELEASE is documented here)
BRICKID int32   Brick ID [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 BRICKID,OBJID; OBJID spans [0,N-1] and is contiguously enumerated within each blob
TYPE char[4]   Morphological model: "PSF"=stellar, "SIMP"="simple galaxy" = 0.45" round EXP galaxy, "EXP"=exponential, "DEV"=deVauc, "COMP"=composite. Note that in some FITS readers, a trailing space may be appended for "PSF ", "EXP " and "DEV " since the column data type is a 4-character string
RA float64 deg Right ascension at epoch J2000
DEC float64 deg Declination at epoch J2000
RA_IVAR float32 1/deg² Inverse variance of RA, excluding astrometric calibration errors
DEC_IVAR float32 1/deg² Inverse variance of DEC (no cos term!), excluding astrometric calibration errors
DCHISQ float32[5]   Difference in χ² between successively more-complex model fits: PSF, SIMPle, EXP, DEV, COMP. 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 \(W1\)
FLUX_W2 float32 nanomaggies WISE model flux in \(W2\)
FLUX_W3 float32 nanomaggies WISE model flux in \(W3\)
FLUX_W4 float32 nanomaggies WISE model flux in \(W4\)
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
FLUX_IVAR_W2 float32 1/nanomaggies² Inverse variance of FLUX_W2
FLUX_IVAR_W3 float32 1/nanomaggies² Inverse variance of FLUX_W3
FLUX_IVAR_W4 float32 1/nanomaggies² Inverse variance of FLUX_W4
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 \(g\)
ANYMASK_R int16   Bitwise mask set if the central pixel from any image satisfies each condition in \(r\)
ANYMASK_Z int16   Bitwise mask set if the central pixel from any image satisfies each condition in \(z\)
ALLMASK_G int16   Bitwise mask set if the central pixel from all images satisfy each condition in \(g\)
ALLMASK_R int16   Bitwise mask set if the central pixel from all images satisfy each condition in \(r\)
ALLMASK_Z int16   Bitwise mask set if the central pixel from all images satisfy each condition in \(z\)
WISEMASK_W1 uint8   W1 bright star bitmask, \(2^0\) \((2^1)\) for southward (northward) scans
WISEMASK_W2 uint8   W2 bright star bitmask, \(2^0\) \((2^1)\) for southward (northward) scans
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
WISE_COADD_ID char[8]   unWISE coadd file name for the center of each object
FRACDEV float32   Fraction of model in deVauc [0,1]
FRACDEV_IVAR float32   Inverse variance of FRACDEV
SHAPEDEV_R float32 arcsec Half-light radius of deVaucouleurs model (>0)
SHAPEDEV_R_IVAR float32 1/arcsec Inverse variance of SHAPEDEV_R
SHAPEDEV_E1 float32   Ellipticity component 1
SHAPEDEV_E1_IVAR float32   Inverse variance of SHAPEDEV_E1
SHAPEDEV_E2 float32   Ellipticity component 2
SHAPEDEV_E2_IVAR float32   Inverse variance of SHAPEDEV_E2
SHAPEEXP_R float32 arcsec Half-light radius of exponential model (>0)
SHAPEEXP_R_IVAR float32 1/arcsec2 Inverse variance of SHAPEEXP_R
SHAPEEXP_E1 float32   Ellipticity component 1
SHAPEEXP_E1_IVAR float32   Inverse variance of SHAPEEXP_E1
SHAPEEXP_E2 float32   Ellipticity component 2
SHAPEEXP_E2_IVAR float32   Inverse variance of SHAPEEXP_E2

Image Stacks

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

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

FITS binary table with the list of CCD images that were used in this brick. Same columns as survey-ccds-*.fits.gz, except for photometric and bitmask, and with the additional columns:

Column Type Description
extname char[4] (ignore)
ccd_cuts int32 (ignore)
ccd_x0 int16 Minimum x image coordinate overlapping this brick
ccd_x1 int16 Maximum x image coordinate overlapping this brick
ccd_y0 int16 Minimum y 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
sig1 float64 (ignore)
psfnorm float32 Same as psfnorm in the ccds-annotated- file
galnorm float64 Same as galnorm in the ccds-annotated- file
plver char[4] Community Pipeline (CP) version
skyver char[17] Git version of the sky calibration code
wcsver char[1] Git version of the WCS calibration code
psfver char[12] Git version of the PSF calibration code
skyplver char[4] CP version of the input to sky calibration
wcsplver char[4] CP version of the input to WCS calibration
psfplver char[4] CP version of the input to PSF calibration

coadd/<AAA>/<brick>/legacysurvey-<brick>-image-<filter>.fits

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: that these images are resampled using Lanczos-3 resampling.

coadd/<AAA>/<brick>/legacysurvey-<brick>-invvar-<filter>.fits

Corresponding stacked inverse variance image 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.

coadd/<AAA>/<brick>/legacysurvey-<brick>-model-<filter>.fits.gz

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.

coadd/<AAA>/<brick>/legacysurvey-<brick>-chi2-<filter>.fits

Stacked χ² image, which is approximately the summed χ² values from the single-epoch images.

coadd/<AAA>/<brick>/legacysurvey-<brick>-depth-<filter>.fits.gz

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(depth_ivar) .

coadd/<AAA>/<brick>/legacysurvey-<brick>-galdepth-<filter>.fits.gz

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(galdepth_ivar) .

coadd/<AAA>/<brick>/legacysurvey-<brick>-nexp-<filter>.fits.gz

Number of exposures contributing to each pixel of the stacked images.

coadd/<AAA>/<brick>/legacysurvey-<brick>-image.jpg

JPEG image of calibrated image using the g,r,z filters as the colors.

coadd/<AAA>/<brick>/legacysurvey-<brick>-model.jpg

JPEG image of the Tractor's model image using the g,r,z filters as the colors.

coadd/<AAA>/<brick>/legacysurvey-<brick>-resid.jpg

JPEG image of the residual image (data minus model) using the g,r,z filters as the colors.

Raw Data

NOAO access to raw and calibrated images will be available starting on July 10, 2017.

Raw and Calibrated Legacy Survey images are available from the NOAO 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 from the Mayall \(z\)-band Legacy Survey (MzLS) in the \(z\) band, and from the Beijing-Arizona Sky Survey (BASS) in the \(g\) & \(r\) bands.

(i) Web interface

  1. Query the NOAO Science Archive.
  2. From the menu of "Available Collections" on the left, select the desired data release (e.g. LS-DR4).
  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-dr4.fits.gz for DR4. 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).