Datamodel: speclya

General Description

The speclya-PLATE-MJD-FIBER.fits files, produced only for z > 2.15 BOSS quasars, extends the "lite" version of the per-object spec format with additional products to assist in Lyman-alpha forest analysis, as described in the DR9 Lyman-alpha Forest Release Paper. Four additional vectors are stored in HDU 1 of each file:

  MASK_COMB   : Combined mask accounting for pipeline masks, sky lines, and DLA cores
  NOISE_CORR  : Correction to make the pipeline noise estimate more accurate.
                Divide flux errors by this, or equivalently multiply the
                pipeline inverse variance (ivar) by the square of this.
  DLA_CORR    : Correction for DLA damping wings. Multiply fluxes by this.
  CONT        : Quasar continuum estimate in the restframe 1040-1600A range,
                estimated using the MF-PCA method. Divide fluxes by this to
                get Lyman-alpha forest transmission fraction.

All other HDUs remain the same as in the "lite" spec files. These files should be used in conjunction with BOSSLyaDR9_cat, which is a catalog listing all spectra in the sample. The speclya files are distributed in a gzipped tarball BOSSLyaDR9_spectra.tar.gz [7GB].

Naming Convention
speclya-[0-9]{4}-[0-9]{5}-[0-9]{4}\.fits, where [0-9]{4} is a zero-padded, four-digit number containing the plate number, [0-9]{5} is a five-digit number containing the MJD number and [0-9]{4} is a four-digit number containing the fiber id.
Approximate Size
295 KB
File Type
FITS

HDU 0: Header keywords only

Identical to HDU 0 of the spec files.

Copied from spPlate with the following additions/modifications:

HDU 1 (extname COADD): Coadded Spectrum from spPlate with Additional Products

The contents of this HDU are the same as HDU 1 of the spec files, with the addition of 4 extra products to aid in Lyman-alpha forest analysis. The headers have also been extended to mirror some information from BOSSLyaDR9_cat.

Additional Header Keywords
KEYTypeComment
SNRfloatS/N per pix in 1268-1380 Ang restframe
SNR_LYAfloatS/N per pix in 1041-1185 Ang restframe
CH_CONTfloatChi-squared for continuum fit in 1220-1600 Ang restframe
CONTFLGintQuality flag for continuum fit
CONTTPTstrQSO spectral template used for continuum fit
Required Columns
Name Type Comment
FLUX float32 coadded calibrated flux [10-17 ergs/s/cm2/Å]
LOGLAM float32 log10(wavelength [Å])
IVAR float32 inverse variance of flux
AND_MASK int32 AND mask
OR_MASK int32 OR mask
WDISP float32 wavelength dispersion in pixel=dloglam units
SKY float32 subtracted sky flux [10-17 ergs/s/cm2/Å]
MODEL float32 pipeline best model fit used for classification and redshift
MASK_COMBint32combined mask incorporating pipeline AND_MASK, sky-line masks, and DLA masks
DLA_CORRfloat32flux correction for known DLAs
NOISE_CORRfloat32pipeline noise corrections
CONTfloat32estimated quasar continuum in 1040-1600 Ang restframe [10-17 ergs/s/cm2/Å]

HDU 2 (extname SPALL)

Identical to HDU 2 of the spec files.

Copy of row from spAll for this (plate, mjd, fiber)

HDU 3 (extname SPZLINE)

Identical to HDU 3 of the spec files.

Copy of row from spZLine for this (plate, mjd, fiber)

Examples

To extract Lyman-alpha forest transmission and corresponding pixel error:

  F = FLUX * DLA_CORR / (CONT * RESIDCORR)
  SIGMA_F = (IVAR * RESIDCORR^2 * NOISE_CORR^2 * CONT^2 / DLA_CORR^2)^(-1/2)
where RESIDCORR is interpolated from residcorr_v5_4_45.dat . Using our continuum, the maximum permissible Lyman-alpha forest interval is 1041-1185 Ang restframe with respect to Z_VI in BOSSLyaDR9_cat, and all pixels with MASK_COMB !=0 or IVAR=0 should be discarded.