Iron fastspec VAC (DR1)

Overview

This page describes the Iron fastspec value-added catalog, which contains full spectrophotometric fitting results (continuum + emission lines) and was publicly released in March 2025 as part of DESI Data Release 1 (DESI/DR1). For the companion photometry-only catalog, see the Iron fastphot VAC.

Please refer to the Acknowledgments section for the conditions for using this VAC.

Note

We only document the latest version of this VAC here; please see below for information regarding previous versions.

Data Content & Access

Data from the Iron VAC can be accessed at any of the following links:

Data url

https://data.desi.lbl.gov/public/dr1/vac/dr1/fastspecfit/iron/v3.0

NERSC (for collaborators)

/global/cfs/cdirs/desi/public/dr1/vac/dr1/fastspecfit/iron/v3.0

For more information regarding the content and organization of the VAC, please click on the following links:

Summary Statistics

The following tables summarize the size and number of targets in each merged catalog, organized by survey and program.

File Name

File Size

Number of Targets

fastspec-iron-cmx-other.fits

12 MB

2,762

File Name

File Size

Number of Targets

fastspec-iron-sv1-backup.fits

14.5 MB

3,331

fastspec-iron-sv1-bright.fits

542 MB

126,650

fastspec-iron-sv1-dark.fits

997 MB

233,202

fastspec-iron-sv1-other.fits

146 MB

34,112

Total (sv1)

1.66 GB

397,295

File Name

File Size

Number of Targets

fastspec-iron-sv2-backup.fits

647 KB

105

fastspec-iron-sv2-bright.fits

199 MB

46,486

fastspec-iron-sv2-dark.fits

225 MB

52,690

Total (sv2)

425 MB

99,281

File Name

File Size

Number of Targets

fastspec-iron-sv3-backup.fits

6.7 MB

1,524

fastspec-iron-sv3-bright.fits

1.11 GB

265,293

fastspec-iron-sv3-dark.fits

2.48 GB

592,191

Total (sv3)

3.6 GB

859,008

File Name

File Size

Number of Targets

fastspec-iron-special-backup.fits

2.49 MB

552

fastspec-iron-special-bright.fits

181 MB

43,261

fastspec-iron-special-dark.fits

62.6 MB

14,954

fastspec-iron-special-other.fits

178 MB

42,064

Total (special)

424 MB

100,831

File Name

File Size

Number of Targets

fastspec-iron-main-backup.fits

63.4 MB

15,163

fastspec-iron-main-bright-nside1-hp00.fits

427 MB

101,838

fastspec-iron-main-bright-nside1-hp01.fits

4.16 GB

1,017,041

fastspec-iron-main-bright-nside1-hp02.fits

5.56 GB

1,358,627

fastspec-iron-main-bright-nside1-hp03.fits

1.65 GB

403,581

fastspec-iron-main-bright-nside1-hp04.fits

4.02 GB

981,600

fastspec-iron-main-bright-nside1-hp05.fits

1.23 GB

301,057

fastspec-iron-main-bright-nside1-hp06.fits

5.51 GB

1,347,464

fastspec-iron-main-bright-nside1-hp07.fits

2.76 GB

673,711

fastspec-iron-main-bright-nside1-hp08.fits

343 MB

81,734

fastspec-iron-main-bright-nside1-hp09.fits

280 MB

66,856

fastspec-iron-main-bright-nside1-hp10.fits

191 MB

45,570

fastspec-iron-main-bright-nside1-hp11.fits

280 MB

66,848

fastspec-iron-main-dark-nside1-hp00.fits

1.44 GB

352,447

fastspec-iron-main-dark-nside1-hp01.fits

4.58 GB

1,118,746

fastspec-iron-main-dark-nside1-hp02.fits

6.96 GB

1,699,122

fastspec-iron-main-dark-nside1-hp03.fits

901 MB

214,658

fastspec-iron-main-dark-nside1-hp04.fits

7.13 GB

1,739,317

fastspec-iron-main-dark-nside1-hp05.fits

2.37 GB

579,026

fastspec-iron-main-dark-nside1-hp06.fits

11.7 GB

2,851,879

fastspec-iron-main-dark-nside1-hp07.fits

4.23 GB

1,032,151

fastspec-iron-main-dark-nside1-hp08.fits

910 MB

216,757

fastspec-iron-main-dark-nside1-hp09.fits

657 MB

156,454

fastspec-iron-main-dark-nside1-hp10.fits

313 MB

74,463

fastspec-iron-main-dark-nside1-hp11.fits

171 MB

40,609

Total (main)

67.7 GB

16,536,719

The following tables summarize the number of QSO targets whose redshift has been updated using the procedure documented here.

Catalog

Number of Objects

Number with Corrected Redshifts

fastspec-iron-cmx-other.fits

2,762

33

Catalog

Number of Objects

Number with Corrected Redshifts

fastspec-iron-sv1-backup.fits

3,331

41

fastspec-iron-sv1-bright.fits

126,650

27

fastspec-iron-sv1-dark.fits

233,202

2,246

fastspec-iron-sv1-other.fits

34,112

69

Total (sv1)

397,295

2,383

Catalog

Number of Objects

Number with Corrected Redshifts

fastspec-iron-sv2-backup.fits

105

0

fastspec-iron-sv2-bright.fits

46,486

1

fastspec-iron-sv2-dark.fits

52,690

485

Total (sv2)

99,281

486

Catalog

Number of Objects

Number with Corrected Redshifts

fastspec-iron-sv3-backup.fits

1,524

0

fastspec-iron-sv3-bright.fits

265,293

33

fastspec-iron-sv3-dark.fits

592,191

1,872

Total (sv3)

859,008

1,905

Catalog

Number of Objects

Number with Corrected Redshifts

fastspec-iron-special-backup.fits

552

0

fastspec-iron-special-bright.fits

43,261

2

fastspec-iron-special-dark.fits

14,954

162

fastspec-iron-special-other.fits

42,064

0

Total (special)

100,831

164

Catalog

Number of Objects

Number with Corrected Redshifts

fastspec-iron-main-backup.fits

15,163

0

fastspec-iron-main-bright-nside1-hp00.fits

101,838

7

fastspec-iron-main-bright-nside1-hp01.fits

1,017,041

61

fastspec-iron-main-bright-nside1-hp02.fits

1,358,627

95

fastspec-iron-main-bright-nside1-hp03.fits

403,581

21

fastspec-iron-main-bright-nside1-hp04.fits

981,600

50

fastspec-iron-main-bright-nside1-hp05.fits

301,057

19

fastspec-iron-main-bright-nside1-hp06.fits

1,347,464

99

fastspec-iron-main-bright-nside1-hp07.fits

673,711

27

fastspec-iron-main-bright-nside1-hp08.fits

81,734

7

fastspec-iron-main-bright-nside1-hp09.fits

66,856

4

fastspec-iron-main-bright-nside1-hp10.fits

45,570

2

fastspec-iron-main-bright-nside1-hp11.fits

66,848

2

fastspec-iron-main-dark-nside1-hp00.fits

352,447

3,080

fastspec-iron-main-dark-nside1-hp01.fits

1,118,746

9,187

fastspec-iron-main-dark-nside1-hp02.fits

1,699,122

11,118

fastspec-iron-main-dark-nside1-hp03.fits

214,658

2,319

fastspec-iron-main-dark-nside1-hp04.fits

1,739,317

15,201

fastspec-iron-main-dark-nside1-hp05.fits

579,026

3,798

fastspec-iron-main-dark-nside1-hp06.fits

2,851,879

13,900

fastspec-iron-main-dark-nside1-hp07.fits

1,032,151

6,267

fastspec-iron-main-dark-nside1-hp08.fits

216,757

2,063

fastspec-iron-main-dark-nside1-hp09.fits

156,454

672

fastspec-iron-main-dark-nside1-hp10.fits

74,463

451

fastspec-iron-main-dark-nside1-hp11.fits

40,609

463

Total (main)

16,536,719

68,913

Code & Template Versions

The following tables document the code versions and environment variables used to produce this VAC. For details regarding the revision history of FastSpecFit, please see the change log.

Software Package

Version(s)

python

3.10.14

numpy

1.22.4

scipy

1.8.1

astropy

6.0.1

yaml

6.0.1

matplotlib

3.8.4

fitsio

1.2.1

mpi4py

3.1.6

healpy

1.16.6

desiutil

3.4.3

desispec

0.68.1

desitarget

2.8.0

speclite

0.20

fastspecfit

3.1.5

Environment Variable

Value

DESI_ROOT

/global/cfs/cdirs/desi

DUST_DIR

/dvs_ro/cfs/cdirs/desi/external/dust/v0_1

FPHOTO_DIR

/dvs_ro/cfs/cdirs/desi/external/legacysurvey/dr9

FTEMPLATES_DIR

/dvs_ro/cfs/cdirs/desi/public/external/templates/fastspecfit

FTEMPLATES_FILE

ftemplates-chabrier-2.0.0.fits (see README.txt)

Notes & Known Issues

v3.0 (latest release)

  • Release date: June 2025

  • FastSpecFit version: 3.1.5

  • Templates: ftemplates-chabrier-2.0.0.fits (see README.txt).

  • Notes:

    • Near-total rewrite of the stellar continuum and emission-line fitting engines, resulting in improved accuracy and significantly faster execution [PR/#177, PR/#186].

    • Updated rest wavelengths and emission-line list; broad He I lines removed [PR/#179].

    • Monte Carlo uncertainties added for all fitted model parameters (e.g., line fluxes, equivalent widths, stellar masses) [PR/#189].

    • Updated theoretical [N II] 6548, 6584 and [O III] 4959, 5007 doublet ratios [PR/#195].

    • Updated algorithm for correcting QSO redshifts [PR/#201].

    • Backwards-incompatible data model update; large merged catalogs now split into separate SPECPHOT and FASTSPEC extensions [PR/#197, PR/#211].

    • Bug fix: <1% bias in fluxes and equivalent widths of tied and free doublet ratios [PR/#198].

    • Bug fix: significant errors in flux and equivalent-width inverse-variance estimates [PR/#213].

  • Known issues:

    • Bug: Poor line fits for a small fraction of strong emission lines due to a clipping error in the ivar2var function (fixed in 3.2.0; see PR/#228).

v2.1

  • Release date: January 2024

  • FastSpecFit version: 2.5.0

  • Templates: ftemplates-chabrier-1.3.0.fits (see README.txt).

  • Notes:

    • Several updates to the spectrophotometric templates aimed at addressing the stellar mass bias identified in issue/#159 (see PR/#166):

      • Templates are now just solar metallicity (previously 0.1, 1, and 1.6 times solar).

      • Five age bins now (vs 8 previously).

      • Expanded velocity dispersion grid (new measurable maximum value is now 475 km/s).

    • Correction to how the light-weighted ages, dust attenuations, and SFRs were being computed.

    • When fitting the broad+narrow emission-line model, [OIII] 4959,5007 is now fitted separately and the narrow Balmer+helium+forbidden line-widths and velocity shifts are all tied together.

    • All known bugs fixed.

  • Known issues:

    • None at this time.

v2.0

  • Release date: August 2023

  • FastSpecFit versions: 2.4.1, 2.4.2

  • Templates: ftemplates-chabrier-1.1.0.fits (see README.txt).

  • Notes:

    • Minor updates to spectrophotometric templates.

    • Just two rounds of emission-line fitting, not three (see PR/#151).

    • Updated IGM attenuation coefficients (see PR/#136).

    • Major algorithmic updates related to how emission-line amplitudes, fluxes, and inverse variances are computed, including a bug fix which the emission-line model spectra were not being convolved with the resolution matrix (see PR/#137).

  • Known Issues:

    • Warning: Stellar masses are systematically higher (by 0.2-0.5 dex) compared to other methods, so they should be used with caution (see issue/#159). Similarly, star-formation rates and other SPS model parameters have not been fully validated.

    • Bug: Fluxes (and EWs) of lines which lie in the camera-overlap region are overestimated by a factor of 2 due to a bug handling the different pixel scale (fixed in PR/#157).

v1.0

  • Release date: February 2023

  • FastSpecFit versions: 2.1.0, 2.1.1

  • Templates: ftemplates-chabrier-1.0.0.fits (see README.txt).

  • Known Issues:

    • Bug: [OII] 7320,7330 doublet amplitude ratio incorrectly inverted (fixed in PR/#120).

    • Bug: Artificial redshift dependence in derived stellar masses due to age prior (fixed in PR/#132).

    • Bug: Emission-line subtracted Dn(4000) values incorrectly computed (fixed in PR/#135).