randoms

Summary:

DESI inside-the-footprint random catalogs contain a single binary table covering the entire Legacy Surveys footprint. They contain meta information (the number of observations, the depth, etc.) derived from pixels in Legacy Surveys CCDs at random RA/Dec coordinates.

Naming Convention:

randoms-seed-iteration.fits, where seed represents the random seed used to generate the catalog and iteration lists the iteration number of the catalog (several iterations are typically conducted during a given run to generate random catalogs).

Regex:

randoms(-[0-9]+)?-[0-9]+\.fits

File Type:

FITS, 14 GB

Contents

Number	EXTNAME	Type	Contents
HDU0		IMAGE	Empty
HDU1	RANDOMS	BINTABLE	Random catalog table

FITS Header Units

HDU0

This HDU has no non-standard required keywords.

Empty HDU.

HDU1

EXTNAME = RANDOMS

Random catalog table

Required Header Keywords

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	281	int	Width of table in bytes
NAXIS2	1124357626	int	Number of rows in table
FILENSID	2	int	HEALPix nside covered by file
FILENEST	T	bool	HEALPix nested (not ring) ordering
FILEHPX	11,5,4	str	HEALPix pixel(s) covered by file
DR	9	int	Legacy Surveys (LS) Data Release used to generate randoms
DENSITY	45000	int	Number of random points generated per sq. deg.
APRAD	0.75	float	Aperture radius used to calculate flux-related quantities (arcsec)
SEED	1	int	Seed used to generate random catalog
ADDMTL	F	bool	True if MTL-related columns were added to the parent catalog used to build this catalog
HPXNSIDE	64	int	HEALPix nside
HPXNEST	T	bool	HEALPix nested (not ring) ordering
SUPP	F	bool	True if randoms were generated without using LS pixels
RESOLVE	T	bool	True if from unique imaging
RESEED	626	int	Seed used to re-shuffle combined random catalogs to ensure randomness
MTLSPLIT	T	bool	True if MTL-related columns were added to this random catalog
REGION [1]	north	str	“noresolve” randoms may have this keyword set. Values are ‘north’ or ‘south’.
INFILE [1]	randoms-1-15.fits	str	HEALPixel-split randoms may have this keyword set. Value is the original source randoms file.

[1] (1,2)

Optional

Required Data Table Columns

Name	Type	Units	Description
RELEASE	int16		Integer denoting the camera and filter set used
BRICKID	int32		A unique Brick ID
BRICKNAME	char[8]		Name of the brick
BRICK_OBJID	int32		Random catalog object number enumerated by increasing RA within each brick; a unique identifier hash is RELEASE,BRICKID,BRICK_OBJID
RA	float64	deg	Right ascension at pixel location
DEC	float64	deg	Declination at pixel location
NOBS_G	int16		Number of images at pixel location in LS g
NOBS_R	int16		Number of images at pixel location in LS r
NOBS_Z	int16		Number of images at pixel location in LS z
PSFDEPTH_G	float32		PSF-based depth at pixel location in LS g
PSFDEPTH_R	float32		PSF-based depth at pixel location in LS r
PSFDEPTH_Z	float32		PSF-based depth at pixel location in LS z
GALDEPTH_G	float32		Galaxy model-based depth at pixel location in LS g
GALDEPTH_R	float32		Galaxy model-based depth at pixel location in LS r
GALDEPTH_Z	float32		Galaxy model-based depth at pixel location in LS z
PSFDEPTH_W1	float32		PSF-based depth in WISE W1 (AB mag system)
PSFDEPTH_W2	float32		PSF-based depth in WISE W2 (AB mag system)
PSFSIZE_G	float32	arcsec	Weighted average PSF FWHM in LS g
PSFSIZE_R	float32	arcsec	Weighted average PSF FWHM in LS r
PSFSIZE_Z	float32	arcsec	Weighted average PSF FWHM in LS z
APFLUX_G	float32	nanomaggy	Total flux extracted in a 0.75 arcsec radius in g
APFLUX_R	float32	nanomaggy	Total flux extracted in a 0.75 arcsec radius in r
APFLUX_Z	float32	nanomaggy	Total flux extracted in a 0.75 arcsec radius in z
APFLUX_IVAR_G	float32	nanomaggy^-2	Inverse variance of APFLUX_G
APFLUX_IVAR_R	float32	nanomaggy^-2	Inverse variance of APFLUX_R
APFLUX_IVAR_Z	float32	nanomaggy^-2	Inverse variance of APFLUX_Z
MASKBITS	int16		Bit mask of possible problems with pixel (see the LS DR9 bitmasks page)
WISEMASK_W1	binary		Bitwise mask for WISE W1 data (see the LS DR9 bitmasks page)
WISEMASK_W2	binary		Bitwise mask for WISE W2 data (see the LS DR9 bitmasks page)
EBV	float32		Galactic extinction E(B-V) reddening at pixel 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 0 (added to facilitate running randoms through the DESI fiberassign code)
MWS_TARGET	int64		See the desitarget data model; set to 0 (added to facilitate running randoms through the DESI fiberassign code)
SUBPRIORITY	float64		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)

Notes and Examples

See http://legacysurvey.org for more details about the corresponding columns for sources extracted by the Tractor in the Legacy Surveys, e.g. the units of the depth quantities.