randoms-allsky

Summary:

DESI allsky random catalogs contain a single binary table covering the entire sky. Inside the Legacy Surveys (LS) footprint they contain meta information (the number of observations, the depth, etc.) derived from pixels in Legacy Surveys CCDs at random RA/Dec coordinates. Outside the LS footprint they contain highly simplified columns. These files are a combination of the standard inside-the-footprint random catalogs and the simplified outside-the-footprint random catalogs.

Naming Convention:

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

File Type:

FITS, 12 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

Required Data Table Columns

Name	Type	Units	Description
RA	float64	deg	Right ascension at pixel location
DEC	float64	deg	Declination at pixel location
BRICKNAME	char[8]		Name of the brick
BRICKID	int32		A unique Brick ID
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

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.