emlineSPECTROGRAPHTILEIDGROUPID.fits¶
 Summary:
This file records simple (Gaussian) emission line fits on the spectra for few major lines.
 Naming Convention:
emlineSPECTROGRAPHTILEIDGROUPID.fits
, whereSPECTROGRAPH
is the spectrograph ID,TILEID
is the tile number andGROUPID
depends on theGROUPTYPE
of the tile coadd. Regex:
emline[09][09]+([14]xsubset[16]lowspeedsubset[16]exp[09]{8}thru[09]{8}[09]{8})\.fits
 File Type:
FITS, 188 KB
Contents¶
Number 
EXTNAME 
Type 
Contents 

IMAGE 
Empty 

EMLINEFIT 
BINTABLE 
Emission line fits table 
FITS Header Units¶
HDU0¶
Empty HDU.
HDU1¶
EXTNAME = EMLINEFIT
Table with the emission line fit results for few major lines.
Required Header Keywords¶
Required Header Keywords Table
KEY 
Example Value 
Type 
Comment 

NAXIS1 
345 
int 
width of table in bytes 
NAXIS2 
500 
int 
number of rows in table 
RRFN 
/global/cfs/cdirs/desi/spectro/redux/fuji/tiles/1x_depth/80608/5/redrock1806081xsubset5.fits 
str 
full path to the redrock file which contains the redshifts 
COADDFN 
/global/cfs/cdirs/desi/spectro/redux/fuji/tiles/1x_depth/80608/5/coadd1806081xsubset5.fits 
str 
full path to the coadd file which contains the spectra 
RFHW 
40 
int 
[Angstrom] restframe wavelength width used for fitting on each side of the line 
MINRFHW 
20 
int 
[Angstrom] minimum requested restframe width on each side of the line to consider the fitting 
RFCONTW 
200 
int 
[Angstrom] restframe wavelength extent to fit the continuum 
RV 
3.1 
float 
value of R_V to convert EBV to magnitudes 
EMNAMES 
OII,HDELTA,HGAMMA,HBETA,OIII,HALPHA 
str 
commaseparated list of emission lines to fit 
RFWAVE00 
3727.092,3729.874 
str 
[Angstrom] restframe, vacuum, wavelength for the first emission line to fit 
RFWAVE01 
4102.892 
str 
[Angstrom] restframe, vacuum, wavelength for the second emission line to fit 
RFWAVE02 
4341.684 
str 
[Angstrom] restframe, vacuum, wavelength for the third emission line to fit 
RFWAVE03 
4862.683 
str 
[Angstrom] restframe, vacuum, wavelength for the forth emission line to fit 
RFWAVE04 
4960.295,5008.239 
str 
[Angstrom] restframe, vacuum, wavelength for the fifth emission line to fit 
RFWAVE05 
6564.613 
str 
[Angstrom] restframe, vacuum, wavelength for the sixth emission line to fit 
Required Data Table Columns¶
Name 
Type 
Units 
Description 

TARGETID 
int64 
Unique DESI target ID 

Z 
float64 
Redshift measured by Redrock 

ZWARN 
int64 
Redshift warning bitmask from Redrock 

SPECTYPE 
char[6] 
Spectral type of Redrock best fit template (e.g. GALAXY, QSO, STAR) 

DELTACHI2 
float64 
chi2 difference between first and secondbest redrock template fits 

TARGET_RA 
float64 
deg 
Target right ascension 
TARGET_DEC 
float64 
deg 
Target declination 
OBJTYPE 
char[3] 
Object type: TGT, SKY, NON, BAD 

OII_FLUX 
float32 
10**17 erg/(s cm2) 
Fitted flux for the [OII] doublet 
OII_FLUX_IVAR 
float32 
10**+34 (s2 cm4) / erg2 
Inverse variance of the fitted flux for the [OII] doublet 
OII_SIGMA 
float32 
Angstrom 
Fitted line width (in the observed frame) for the [OII] doublet 
OII_SIGMA_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted line width (in the observed frame) for the [OII] doublet 
OII_CONT 
float32 
10**17 erg/(s cm2 Angstrom) 
Continuum used for the fitting (fixed value) for the [OII] doublet 
OII_CONT_IVAR 
float32 
10**+34 (s2 cm4 Angstrom2) / erg2 
Inverse variance of the continuum for the [OII] doublet 
OII_SHARE 
float32 
Fitted F1/(F0+F1) for the [OII] doublet, where F0 and F1 are the individual line fluxes 

OII_SHARE_IVAR 
float32 
Inverse variance of the fitted F1/(F0+F1) for the [OII] doublet 

OII_EW 
float32 
Angstrom 
Fitted restframe equivalent width for the [OII] doublet 
OII_EW_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted restframe equivalent width for the [OII] doublet 
OII_CHI2 
float32 
Reduced chi2 of the fit for the [OII] doublet 

OII_NDOF 
int32 
Number of degrees of freedom of the fit for the [OII] doublet 

HDELTA_FLUX 
float32 
10**17 erg/(s cm2) 
Fitted flux for the HDELTA line 
HDELTA_FLUX_IVAR 
float32 
10**+34 (s2 cm4) / erg2 
Inverse variance of the fitted flux for the HDELTA line 
HDELTA_SIGMA 
float32 
Angstrom 
Fitted line width (in the observed frame) for the HDELTA line 
HDELTA_SIGMA_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted line width (in the observed frame) for the HDELTA line 
HDELTA_CONT 
float32 
10**17 erg/(s cm2 Angstrom) 
Continuum used for the fitting (fixed value) for the HDELTA line 
HDELTA_CONT_IVAR 
float32 
10**+34 (s2 cm4 Angstrom2) / erg2 
Inverse variance of the continuum for the HDELTA line 
HDELTA_SHARE 
float32 
NaN (SHARE not relevant for HDELTA line) 

HDELTA_SHARE_IVAR 
float32 
NaN (SHARE not relevant for HDELTA line) 

HDELTA_EW 
float32 
Angstrom 
Fitted restframe equivalent width for the HDELTA line 
HDELTA_EW_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted restframe equivalent width for the HDELTA line 
HDELTA_CHI2 
float32 
Reduced chi2 of the fit for the HDELTA line 

HDELTA_NDOF 
int32 
Number of degrees of freedom of the fit for the HDELTA line 

HGAMMA_FLUX 
float32 
10**17 erg/(s cm2) 
Fitted flux for the HGAMMA line 
HGAMMA_FLUX_IVAR 
float32 
10**+34 (s2 cm4) / erg2 
Inverse variance of the fitted flux for the HGAMMA line 
HGAMMA_SIGMA 
float32 
Angstrom 
Fitted line width (in the observed frame) for the HGAMMA line 
HGAMMA_SIGMA_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted line width (in the observed frame) for the HGAMMA line 
HGAMMA_CONT 
float32 
10**17 erg/(s cm2 Angstrom) 
Continuum used for the fitting (fixed value) for the HGAMMA line 
HGAMMA_CONT_IVAR 
float32 
10**+34 (s2 cm4 Angstrom2) / erg2 
Inverse variance of the continuum for the HGAMMA line 
HGAMMA_SHARE 
float32 
NaN (SHARE not relevant for HGAMMA line) 

HGAMMA_SHARE_IVAR 
float32 
NaN (SHARE not relevant for HGAMMA line) 

HGAMMA_EW 
float32 
Angstrom 
Fitted restframe equivalent width for the HGAMMA line 
HGAMMA_EW_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted restframe equivalent width for the HGAMMA line 
HGAMMA_CHI2 
float32 
Reduced chi2 of the fit for the HGAMMA line 

HGAMMA_NDOF 
int32 
Number of degrees of freedom of the fit for the HGAMMA line 

HBETA_FLUX 
float32 
10**17 erg/(s cm2) 
Fitted flux for the HBETA line 
HBETA_FLUX_IVAR 
float32 
10**+34 (s2 cm4) / erg2 
Inverse variance of the fitted flux for the HBETA line 
HBETA_SIGMA 
float32 
Angstrom 
Fitted line width (in the observed frame) for the HBETA line 
HBETA_SIGMA_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted line width (in the observed frame) for the HBETA line 
HBETA_CONT 
float32 
10**17 erg/(s cm2 Angstrom) 
Continuum used for the fitting (fixed value) for the HBETA line 
HBETA_CONT_IVAR 
float32 
10**+34 (s2 cm4 Angstrom2) / erg2 
Inverse variance of the continuum for the HBETA line 
HBETA_SHARE 
float32 
NaN (SHARE not relevant for HBETA line) 

HBETA_SHARE_IVAR 
float32 
NaN (SHARE not relevant for HBETA line) 

HBETA_EW 
float32 
Angstrom 
Fitted restframe equivalent width for the HBETA line 
HBETA_EW_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted restframe equivalent width for the HBETA line 
HBETA_CHI2 
float32 
Reduced chi2 of the fit for the HBETA line 

HBETA_NDOF 
int32 
Number of degrees of freedom of the fit for the HBETA line 

OIII_FLUX 
float32 
10**17 erg/(s cm2) 
Fitted flux for the [OIII] doublet 
OIII_FLUX_IVAR 
float32 
10**+34 (s2 cm4) / erg2 
Inverse variance of the fitted flux for the [OIII] doublet 
OIII_SIGMA 
float32 
Angstrom 
Fitted line width (in the observed frame) for the [OIII] doublet 
OIII_SIGMA_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted line width (in the observed frame) for the [OIII] doublet 
OIII_CONT 
float32 
10**17 erg/(s cm2 Angstrom) 
Continuum used for the fitting (fixed value) for the [OIII] doublet 
OIII_CONT_IVAR 
float32 
10**+34 (s2 cm4 Angstrom2) / erg2 
Inverse variance of the continuum for the [OIII] doublet 
OIII_SHARE 
float32 
F1/(F0+F1) for the [OIII] doublet, where F0 and F1 are the individual line fluxes (SHARE value fixed during the fit) 

OIII_SHARE_IVAR 
float32 
Infinite value, as SHARE is fixed during the fit 

OIII_EW 
float32 
Angstrom 
Fitted restframe equivalent width for the [OIII] doublet 
OIII_EW_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted restframe equivalent width for the [OIII] doublet 
OIII_CHI2 
float32 
Reduced chi2 of the fit for the [OIII] doublet 

OIII_NDOF 
int32 
Number of degrees of freedom of the fit for the [OIII] doublet 

HALPHA_FLUX 
float32 
10**17 erg/(s cm2) 
Fitted flux for the HALPHA line 
HALPHA_FLUX_IVAR 
float32 
10**+34 (s2 cm4) / erg2 
Inverse variance of the fitted flux for the HALPHA line 
HALPHA_SIGMA 
float32 
Angstrom 
Fitted line width (in the observed frame) for the HALPHA line 
HALPHA_SIGMA_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted line width (in the observed frame) for the HALPHA line 
HALPHA_CONT 
float32 
10**17 erg/(s cm2 Angstrom) 
Continuum used for the fitting (fixed value) for the HALPHA line 
HALPHA_CONT_IVAR 
float32 
10**+34 (s2 cm4 Angstrom2) / erg2 
Inverse variance of the continuum for the HALPHA line 
HALPHA_SHARE 
float32 
NaN (SHARE not relevant for HALPHA line) 

HALPHA_SHARE_IVAR 
float32 
NaN (SHARE not relevant for HALPHA line) 

HALPHA_EW 
float32 
Angstrom 
Fitted restframe equivalent width for the HALPHA line 
HALPHA_EW_IVAR 
float32 
Angstrom^2 
Inverse variance of the fitted restframe equivalent width for the HALPHA line 
HALPHA_CHI2 
float32 
Reduced chi2 of the fit for the HALPHA line 

HALPHA_NDOF 
int32 
Number of degrees of freedom of the fit for the HALPHA line 
Notes and Examples¶
The fit is done with the desispec.scripts.emline script.
[OII] is fit as a doublet (3927 and 3929), with the line ratio left free during the fit.
[OIII] is fit as a doublet (4960 and 5007), with the line ratio fixed during the fit.
The SHARE is fitted only for the [OII] doublet; for the [OIII] doublet, its value is fixed (hence the infinite OIII_SHARE_IVAR); for the other lines, the SHARE is not used, and NaN are reported.
If there are not enough pixels to fit or if the fit fails, NaN values are reported.
The default settings are designed for the ELGs (e.g. max_sigma); values to be interpreted with caution for the other targets.
The fitted flux is not forced to be positive, so negative values can happen.
The Z,ZWARN,SPECTYPE,DELTACHI2 (TARGET_RA,TARGET_DEC,OBJTYPE, respectively) columns come from the REDSHIFTS (FIBERMAP, respectively) extension of the input redrock file (see redrockSPECTROGRAPHTILEIDGROUPID).
For the SURVEY=cmx m33 tile (TILEID=80615) tile and all the SURVEY=sv1 tiles (except TILEID=8097180976, the dc3r2 ones), propermotion 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
, andPLATE_REF_EPOCH
.For the fuji (EDR) and guadalupe productions, the equivalent widths are wrong (overestimated) by a factor (1+Z) ** 2; the code bug has been corrected for subsequent productions (e.g. iron).