redrock-SPECTROGRAPH-TILEID-GROUPID.fits¶

Summary:: Redshifts and spectral classifications from Redrock.
Naming Convention:: redrock-SPECTROGRAPH-TILEID-GROUPID.fits, where SPECTROGRAPH is the spectrograph ID, TILEID is the tile number and GROUPID depends on the GROUPTYPE of the tile coadd.
Regex:: redrock-[0-9]-[0-9]+-([14]xsubset[1-6]|lowspeedsubset[1-6]|exp[0-9]{8}|thru[0-9]{8}|[0-9]{8})\.fits
File Type:: FITS, 450 KB

This file contains spectral classifications and redshifts for spectra coadded across exposures of an individual tile. For a similar file that also combined data across multiple tiles, see healpix-based Redrock files.

Contents¶

Number	EXTNAME	Type	Contents
HDU0		IMAGE	Keywords only
HDU1	REDSHIFTS	BINTABLE	Table with redshifts and spectral classifications
HDU2	FIBERMAP	BINTABLE	Target photometry, metadata, and what fibers they are assigned to
HDU3	EXP_FIBERMAP	BINTABLE	Per-exposure entries from input fibermaps
HDU4	TSNR2	BINTABLE	Template signal-to-noise values from input coadd SCORES table

FITS Header Units¶

HDU0¶

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
LONGSTRN	OGIP 1.0	str
RRVER	0.15.0	str	Redrock version
TEMNAM00	GALAXY	str	Redrock template 00 name
TEMVER00	2.6	str	Redrock template 00 version
TEMNAM01	QSO	str
TEMVER01	0.1	str
TEMNAM02	STAR:::A	str
TEMVER02	0.1	str
TEMNAM03	STAR:::B	str
TEMVER03	0.1	str
TEMNAM04	STAR:::CV	str
TEMVER04	0.1	str
TEMNAM05	STAR:::F	str
TEMVER05	0.1	str
TEMNAM06	STAR:::G	str
TEMVER06	0.1	str
TEMNAM07	STAR:::K	str
TEMVER07	0.1	str
TEMNAM08	STAR:::M	str
TEMVER08	0.1	str
TEMNAM09	STAR:::WD	str
TEMVER09	0.1	str
SPGRP	cumulative	str	Exposure grouping (pernight, cumulative, …)
SPGRPVAL	20210205	int	Value of grouping (night, expid, …)
TILEID	80605	int	DESI Tile ID
SPECTRO	6	int	Spectrograph number
PETAL	6	int	Focal plane petal number (same as SPECTRO)
NIGHT [1]	20210205	int	(Last) night of data included, if applicable to grouping

Empty HDU.

HDU1¶

EXTNAME = REDSHIFTS

Spectral classifications and redshifts from Redrock.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	170	int	Width of table in bytes
NAXIS2	500	int	Number of targets in table

Required Data Table Columns¶

Name	Type	Description
TARGETID	int64	Unique DESI target ID
CHI2	float64	Best fit chi squared
COEFF	float64[10]	Redrock template coefficients
Z	float64	Redshift measured by Redrock
ZERR	float64	Redshift error from redrock
ZWARN	int64	Redshift warning bitmask from Redrock
NPIXELS	int64	Number of unmasked pixels contributing to the Redrock fit
SPECTYPE	char[6]	Spectral type of Redrock best fit template (e.g. GALAXY, QSO, STAR)
SUBTYPE	char[20]	Spectral subtype
NCOEFF	int64	Number of Redrock template coefficients
DELTACHI2	float64	chi2 difference between first- and second-best redrock template fits

HDU2¶

EXTNAME = FIBERMAP

Fibermap with target metadata such as photometry, target selection bits, and what fibers each target was assigned to. This table is row-matched to the REDSHIFTS table.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	371	int	Width of table in bytes
NAXIS2	500	int	Number of targets in table.

Required Data Table Columns¶

Name	Type	Units	Description
TARGETID	int64		Unique DESI target ID
PETAL_LOC	int16		Petal location [0-9]
DEVICE_LOC	int32		Device location on focal plane [0-523]
LOCATION	int64		Location on the focal plane PETAL_LOC*1000 + DEVICE_LOC
FIBER	int32		Fiber ID on the CCDs [0-4999]
COADD_FIBERSTATUS	int32		bitwise-AND of input FIBERSTATUS
TARGET_RA	float64	deg	Barycentric right ascension in ICRS
TARGET_DEC	float64	deg	Barycentric declination in ICRS
PMRA	float32	mas yr^-1	proper motion in the +RA direction (already including cos(dec))
PMDEC	float32	mas yr^-1	Proper motion in the +Dec direction
REF_EPOCH	float32	yr	Reference epoch for Gaia/Tycho astrometry. Typically 2015.5 for Gaia
LAMBDA_REF	float32	Angstrom	Requested wavelength at which targets should be centered on fibers
FA_TARGET	int64		Targeting bit internally used by fiberassign (linked with FA_TYPE)
FA_TYPE	binary		Fiberassign internal target type (science, standard, sky, safe, suppsky)
OBJTYPE	char[3]		Object type: TGT, SKY, NON, BAD
FIBERASSIGN_X	float32	mm	Fiberassign expected CS5 X location on focal plane
FIBERASSIGN_Y	float32	mm	Fiberassign expected CS5 Y location on focal plane
PRIORITY	int32		Target current priority
SUBPRIORITY	float64		Random subpriority [0-1) to break assignment ties
OBSCONDITIONS	int32		Bitmask of allowed observing conditions
RELEASE	int16		Imaging surveys release ID
BRICKNAME	char[8]		Brick name from tractor input
BRICKID	int32		Brick ID from tractor input
BRICK_OBJID	int32		Imaging Surveys OBJID on that brick
MORPHTYPE	char[4]		Imaging Surveys morphological type from Tractor
EBV	float32	mag	Galactic extinction E(B-V) reddening from SFD98
FLUX_G	float32	nanomaggy	Flux in the Legacy Survey g-band (AB)
FLUX_R	float32	nanomaggy	Flux in the Legacy Survey r-band (AB)
FLUX_Z	float32	nanomaggy	Flux in the Legacy Survey z-band (AB)
FLUX_W1	float32	nanomaggy	WISE flux in W1 (AB)
FLUX_W2	float32	nanomaggy	WISE flux in W2 (AB)
FLUX_IVAR_G	float32	nanomaggy^-2	Inverse variance of FLUX_G (AB)
FLUX_IVAR_R	float32	nanomaggy^-2	Inverse variance of FLUX_R (AB)
FLUX_IVAR_Z	float32	nanomaggy^-2	Inverse variance of FLUX_Z (AB)
FLUX_IVAR_W1	float32	nanomaggy^-2	Inverse variance of FLUX_W1 (AB)
FLUX_IVAR_W2	float32	nanomaggy^-2	Inverse variance of FLUX_W2 (AB)
FIBERFLUX_G	float32	nanomaggy	Predicted g-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERFLUX_R	float32	nanomaggy	Predicted r-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERFLUX_Z	float32	nanomaggy	Predicted z-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERTOTFLUX_G	float32	nanomaggy	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	nanomaggy	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	nanomaggy	Predicted z-band flux within a fiber of diameter 1.5 arcsec from all sources at this location in 1 arcsec Gaussian seeing
MASKBITS	int16		Bitwise mask from the imaging indicating potential issue or blending
SERSIC	float32		Power-law index for the Sersic profile model (MORPHTYPE=”SER”)
SHAPE_R	float32	arcsec	Half-light radius of galaxy model (>0)
SHAPE_E1	float32		Ellipticity component 1 of galaxy model for galaxy type MORPHTYPE
SHAPE_E2	float32		Ellipticity component 2 of galaxy model for galaxy type MORPHTYPE
REF_ID	int64		Tyc11,000,000+Tyc210+Tyc3 for Tycho-2; “sourceid” for Gaia DR2
REF_CAT	char[2]		Reference catalog source for star: “T2” for Tycho-2, “G2” for Gaia DR2, “L2” for the SGA, empty otherwise
GAIA_PHOT_G_MEAN_MAG	float32	mag	Gaia G band magnitude
GAIA_PHOT_BP_MEAN_MAG	float32	mag	Gaia BP band magnitude
GAIA_PHOT_RP_MEAN_MAG	float32	mag	Gaia RP band magnitude
PARALLAX	float32	mas	Reference catalog parallax
PHOTSYS	char[1]		‘N’ for the MzLS/BASS photometric system, ‘S’ for DECaLS
PRIORITY_INIT	int64		Target initial priority from target selection bitmasks and OBSCONDITIONS
NUMOBS_INIT	int64		Initial number of observations for target calculated across target selection bitmasks and OBSCONDITIONS
SV1_DESI_TARGET [1]	int64		DESI (dark time program) target selection bitmask for SV1
SV1_BGS_TARGET [1]	int64		BGS (bright time program) target selection bitmask for SV1
SV1_MWS_TARGET [1]	int64		MWS (bright time program) target selection bitmask for SV1
SV1_SCND_TARGET [1]	int64		Secondary target selection bitmask for SV1
DESI_TARGET	int64		DESI (dark time program) target selection bitmask
BGS_TARGET	int64		BGS (Bright Galaxy Survey) target selection bitmask
MWS_TARGET	int64		Milky Way Survey targeting bits
SCND_TARGET [1]	int64		Target selection bitmask for secondary programs
PLATE_RA	float64	deg	Barycentric Right Ascension in ICRS to be used by PlateMaker
PLATE_DEC	float64	deg	Barycentric Declination in ICRS to be used by PlateMaker
TILEID	int32		Unique DESI tile ID
COADD_NUMEXP	int16		Number of exposures in coadd
COADD_EXPTIME	float32	s	Summed exposure time for coadd
COADD_NUMNIGHT	int16		Number of nights in coadd
COADD_NUMTILE	int16		Number of tiles in coadd
MEAN_DELTA_X	float32	mm	Mean (over exposures) fiber difference requested - actual CS5 X location on focal plane
RMS_DELTA_X	float32	mm	RMS (over exposures) of the fiber difference between measured and requested CS5 X location on focal plane
MEAN_DELTA_Y	float32	mm	Mean (over exposures) fiber difference requested - actual CS5 Y location on focal plane
RMS_DELTA_Y	float32	mm	RMS (over exposures) of the fiber difference between measured and requested CS5 Y location on focal plane
MEAN_PSF_TO_FIBER_SPECFLUX	float32		Mean of input exposures fraction of light from point-like source captured by 1.5 arcsec diameter fiber given atmospheric seeing
MEAN_MJD	float64	d	Mean MJD across fibers contributing to coadd
MEAN_FIBER_X	float32	mm	Mean (over exposures) fiber CS5 X location on focal plane
MEAN_FIBER_Y	float32	mm	Mean (over exposures) fiber CS5 Y location on focal plane
MEAN_FIBER_RA	float64	deg	Mean (over exposures) RA of actual fiber position
STD_FIBER_RA	float32	arcsec	Standard deviation (over exposures) of RA of actual fiber position
MEAN_FIBER_DEC	float64	deg	Mean (over exposures) DEC of actual fiber position
STD_FIBER_DEC	float32	arcsec	Standard deviation (over exposures) of DEC of actual fiber position
MIN_MJD	float64	d	Minimum MJD contributing to fiber coadd
MAX_MJD	float64	d	Maximum MJD contributing to fiber coadd
FIRSTNIGHT	int32		First night tile was observed (YYYYMMDD)
LASTNIGHT	int32		Last night tile was observed (YYYYMMDD)

HDU3¶

EXTNAME = EXP_FIBERMAP

Fibermap entries that vary from exposure to exposure, e.g. what exposures were include in the coadd and what focalplane (x,y) each target was located at for each exposure.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	162	int	Width of table in bytes
NAXIS2	500	int	Number of input target-exposures = rows in table

Required Data Table Columns¶

Name	Type	Units	Description
TARGETID	int64		Unique DESI target ID
PRIORITY	int32		Target current priority
SUBPRIORITY	float64		Random subpriority [0-1) to break assignment ties
NIGHT	int32
EXPID	int32		DESI Exposure ID number
MJD	float64		Modified Julian Date when shutter was opened for this exposure
TILEID	int32		Unique DESI tile ID
EXPTIME	float64	s	Length of time shutter was open
PETAL_LOC	int16		Petal location [0-9]
DEVICE_LOC	int32		Device location on focal plane [0-523]
LOCATION	int64		Location on the focal plane PETAL_LOC*1000 + DEVICE_LOC
FIBER	int32		Fiber ID on the CCDs [0-4999]
FIBERSTATUS	int32		Fiber status mask. 0=good
FIBERASSIGN_X	float32	mm	Fiberassign expected CS5 X location on focal plane
FIBERASSIGN_Y	float32	mm	Fiberassign expected CS5 Y location on focal plane
LAMBDA_REF	float32	Angstrom	Requested wavelength at which targets should be centered on fibers
PLATE_RA	float64	deg	Barycentric Right Ascension in ICRS to be used by PlateMaker
PLATE_DEC	float64	deg	Barycentric Declination in ICRS to be used by PlateMaker
NUM_ITER	int64		Number of positioner iterations
FIBER_X	float64	mm	CS5 X location requested by PlateMaker
FIBER_Y	float64	mm	CS5 Y location requested by PlateMaker
DELTA_X	float64	mm	CS5 X requested minus actual position
DELTA_Y	float64	mm	CS5 Y requested minus actual position
FIBER_RA	float64	deg	RA of actual fiber position
FIBER_DEC	float64	deg	DEC of actual fiber position
PSF_TO_FIBER_SPECFLUX	float64		fraction of light from point-like source captured by 1.5 arcsec diameter fiber given atmospheric seeing

HDU4¶

EXTNAME = TSNR2

Template signal-to-noise squared. These quantities weight the observed (S/N)^2 by which wavelengths matter most for different target types, e.g. QSOs weight blue wavelengths more while ELGs weight redder wavelengths more due to the wavelengths of the observed emission lines. For more details, see section 4.14 of Guy et al 2023.

This table is row-matched to the REDSHIFTS table.

Required Header Keywords¶

Required Header Keywords Table

KEY	Example Value	Type	Comment
NAXIS1	136	int	Width of table in bytes.
NAXIS2	500	int	Number of targets = number of table rows.

Required Data Table Columns¶

Name	Type	Description
TARGETID	int64	Unique DESI target ID
TSNR2_GPBDARK_B	float32
TSNR2_ELG_B	float32	ELG B template (S/N)^2
TSNR2_GPBBRIGHT_B	float32
TSNR2_LYA_B	float32	LYA B template (S/N)^2
TSNR2_BGS_B	float32	BGS B template (S/N)^2
TSNR2_GPBBACKUP_B	float32
TSNR2_QSO_B	float32	QSO B template (S/N)^2
TSNR2_LRG_B	float32	LRG B template (S/N)^2
TSNR2_GPBDARK_R	float32
TSNR2_ELG_R	float32	ELG R template (S/N)^2
TSNR2_GPBBRIGHT_R	float32
TSNR2_LYA_R	float32	LYA R template (S/N)^2
TSNR2_BGS_R	float32	BGS R template (S/N)^2
TSNR2_GPBBACKUP_R	float32
TSNR2_QSO_R	float32	QSO R template (S/N)^2
TSNR2_LRG_R	float32	LRG R template (S/N)^2
TSNR2_GPBDARK_Z	float32
TSNR2_ELG_Z	float32	ELG Z template (S/N)^2
TSNR2_GPBBRIGHT_Z	float32
TSNR2_LYA_Z	float32	LYA Z template (S/N)^2
TSNR2_BGS_Z	float32	BGS Z template (S/N)^2
TSNR2_GPBBACKUP_Z	float32
TSNR2_QSO_Z	float32	QSO Z template (S/N)^2
TSNR2_LRG_Z	float32	LRG Z template (S/N)^2
TSNR2_GPBDARK	float32
TSNR2_ELG	float32	ELG template (S/N)^2 summed over B,R,Z
TSNR2_GPBBRIGHT	float32
TSNR2_LYA	float32	LYA template (S/N)^2 summed over B,R,Z
TSNR2_BGS	float32	BGS template (S/N)^2 summed over B,R,Z
TSNR2_GPBBACKUP	float32
TSNR2_QSO	float32	QSO template (S/N)^2 summed over B,R,Z
TSNR2_LRG	float32	LRG template (S/N)^2 summed over B,R,Z

Notes and Examples¶

The REDSHIFTS, FIBERMAP, and TSNR2 tables are row-matched with one row per target. They also include a TARGETID column for confirmation and database-like joins with other tables. The EXP_FIBERMAP HDU has one row per target-exposure, and thus will have multiple entries per target when a target was observed on multiple input exposures.

This file is for redshifts from an individual spectrograph/petal of an individual tile. For a contatenation of all such files within a given survey and program, see the ztile file.

For the SURVEY=cmx m33 tile (TILEID=80615) tile and all the SURVEY=sv1 tiles (except TILEID=80971-80976, the dc3r2 ones), proper-motion correction was applied at the fiberassign design step; thus the following columns can have different values than in the desitarget products: TARGET_RA, TARGET_DEC, REF_EPOCH, PLATE_RA, PLATE_DEC, and PLATE_REF_EPOCH.

For targets with a non-zero proper motion, FIBER_RA and FIBER_DEC refer to the position at the reference epoch (but note that the proper-motion correction has been applied at the time of the observation, it is just not recorded in FIBER_RA and FIBER_DEC).