pixweight

Summary:

DESI HEALPixel weight files 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, together with target densities, conveniently stored as HEALPixel maps. They are derived from corresponding DESI random catalogs and target files, which are listed in the README file in the parent pixweight directory.

Naming Convention:

PHASEpixweight-SEED-OBSCON.fits, where PHASE is a specific DESI observational phase (e.g. svX with X=1,2,3 for iterations of Survey Validation) OBSCON is the observing condition (or “layer”) for the targets (e.g. dark), and SEED is the random seed used to generate the associated random catalog. PHASE is omitted for Main Survey catalogs.

Regex:

(cmx|sv1|sv2|sv3|main2|)pixweight(-[0-9]+)?-(bright|dark)\.fits

File Type:

FITS, 100 MB

Contents

Number	EXTNAME	Type	Contents
HDU0		IMAGE	Empty
HDU1	PIXWEIGHTS	BINTABLE	pixweight catalog table

FITS Header Units

HDU0

This HDU has no non-standard required keywords.

Empty HDU.

HDU1

EXTNAME = PIXWEIGHTS

pixweight catalog table

Required Header Keywords

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	132	int	Width of table in bytes
NAXIS2	786432	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
GAIALOC	“/global/”	str	Location of file used to generate stellar density
SURVEY	“main”	str	svX for SV, main for Main Survey

Required Data Table Columns

Name	Type	Units	Description
HPXPIXEL	int32		HEALPixel in pixweight map at HPXNSIDE
FRACAREA	float32		Fraction of HEALPixel with at least one observation in any band of the Legacy Surveys
STARDENS	float32	deg^-2	The stellar density in the HEALPixel from Gaia
EBV	float32		E(B-V) in HEALPixel from the SFD98 dust map, from the median EBV in the associated random catalog
PSFDEPTH_G	float32		PSF depth in LS g in the HEALPixel, from the median PSFDEPTH_G in the associated random catalog
PSFDEPTH_R	float32		PSF depth in LS r in the HEALPixel, from the median PSFDEPTH_R in the associated random catalog
PSFDEPTH_Z	float32		PSF depth in LS z in the HEALPixel, from the median PSFDEPTH_Z in the associated random catalog
GALDEPTH_G	float32		Galaxy depth in LS g in the HEALPixel, from the median GALDEPTH_G in the associated random catalog
GALDEPTH_R	float32		Galaxy depth in LS r in the HEALPixel, from the median GALDEPTH_R in the associated random catalog
GALDEPTH_Z	float32		Galaxy depth in LS z in the HEALPixel, from the median GALDEPTH_Z in the associated random catalog
PSFDEPTH_W1	float32		(AB) PSF depth in WISE W1 in the HEALPixel, from the median PSFDEPTH_W1 in the associated random catalog
PSFDEPTH_W2	float32		(AB) PSF depth in WISE W2 in the HEALPixel, from the median PSFDEPTH_W2 in the associated random catalog
PSFSIZE_G	float32	arcsec	Weighted average PSF FWHM in LS g in the HEALPixel, from the median PSFSIZE_G in the associated random catalog
PSFSIZE_R	float32	arcsec	Weighted average PSF FWHM in LS r in the HEALPixel, from the median PSFSIZE_R in the associated random catalog
PSFSIZE_Z	float32	arcsec	Weighted average PSF FWHM in LS z in the HEALPixel, from the median PSFSIZE_Z in the associated random catalog
FRACAREA_12290	float32		Fraction of HEALPixel with at least one observation in any band with LS MASKBITS = X (bitwise OR, so, e.g. if X=7 then fraction for 2^0 | 2^1 | 2^2)
FRACAREA_8194	float32		Fraction of HEALPixel with at least one observation in any band with LS MASKBITS = X (bitwise OR, so, e.g. if X=7 then fraction for 2^0 | 2^1 | 2^2)
ELG	float32	deg^-2	Density of ELG targets in HEALPixel
LRG	float32	deg^-2	Density of LRG targets in HEALPixel
QSO	float32	deg^-2	Density of QSO targets in HEALPixel
BGS_ANY	float32	deg^-2	Density of BGS_ANY targets in HEALPixel
MWS_ANY	float32	deg^-2	Density of MWS_ANY targets in HEALPixel
ALL	float32	deg^-2	Density of all targets in HEALPixel
STD_FAINT	float32	deg^-2	Density of STD_FAINT targets in HEALPixel
STD_BRIGHT	float32	deg^-2	Density of STD_BRIGHT targets in HEALPixel
BGS_FAINT	float32	deg^-2	Density of BGS_FAINT targets in HEALPixel
BGS_BRIGHT	float32	deg^-2	Density of BGS_BRIGHT targets in HEALPixel
BGS_WISE	float32	deg^-2	Density of BGS_WISE targets in HEALPixel
MWS_BROAD	float32	deg^-2	Density of MWS_BROAD targets in HEALPixel
MWS_MAIN_RED	float32	deg^-2	Density of MWS_MAIN_RED targets in HEALPixel
MWS_MAIN_BLUE	float32	deg^-2	Density of MWS_MAIN_BLUE targets in HEALPixel
MWS_WD	float32	deg^-2	Density of MWS_WD targets in HEALPixel
MWS_NEARBY	float32	deg^-2	Density of MWS_NEARBY targets in HEALPixel

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.