Iron VAC (DR1)

Overview

This page describes the Iron value-added catalog, which will be publicly released as part of the DESI Data Release 1 (DESI/DR1) sometime in 2024 (exact date TBD).

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/v2.1

NERSC (for collaborators)

/global/cfs/cdirs/desi/public/dr1/vac/dr1/fastspecfit/iron/v2.1

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

Summary Statistics

The next two tables summarize the size and number of targets in each merged catalog. The first table gives the sample in each survey and program, while the second table combines all the individual programs into separate main, sv, and special catalogs.

File Name

File Size

Number of Targets

fastspec-iron-cmx-other.fits

11.2 MB

2,762

fastspec-iron-main-backup.fits

59.1 MB

15,163

fastspec-iron-main-bright.fits

24.6 GB

6,445,926

fastspec-iron-main-dark.fits

38.5 GB

10,075,557

fastspec-iron-special-backup.fits

2.31 MB

552

fastspec-iron-special-bright.fits

169 MB

43,261

fastspec-iron-special-dark.fits

58.3 MB

14,954

fastspec-iron-special-other.fits

166 MB

42,064

fastspec-iron-sv1-backup.fits

13.6 MB

3,331

fastspec-iron-sv1-bright.fits

506 MB

126,650

fastspec-iron-sv1-dark.fits

931 MB

233,201

fastspec-iron-sv1-other.fits

136 MB

34,112

fastspec-iron-sv2-backup.fits

593 KB

105

fastspec-iron-sv2-bright.fits

186 MB

46,486

fastspec-iron-sv2-dark.fits

211 MB

52,690

fastspec-iron-sv3-backup.fits

6.25 MB

1,524

fastspec-iron-sv3-bright.fits

1.04 GB

265,292

fastspec-iron-sv3-dark.fits

2.32 GB

592,190

fastspec-iron.fits

70.9 GB

17,995,820

The following table summarizes 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

34

fastspec-iron-main-backup.fits

15,163

0

fastspec-iron-main-bright.fits

6,445,926

348

fastspec-iron-main-dark.fits

10,075,557

59,907

fastspec-iron-special-backup.fits

552

0

fastspec-iron-special-bright.fits

43,261

2

fastspec-iron-special-dark.fits

14,954

137

fastspec-iron-special-other.fits

42,064

0

fastspec-iron-sv1-backup.fits

3,331

40

fastspec-iron-sv1-bright.fits

126,650

27

fastspec-iron-sv1-dark.fits

233,201

2,199

fastspec-iron-sv1-other.fits

34,112

67

fastspec-iron-sv2-backup.fits

105

0

fastspec-iron-sv2-bright.fits

46,486

1

fastspec-iron-sv2-dark.fits

52,690

485

fastspec-iron-sv3-backup.fits

1,524

0

fastspec-iron-sv3-bright.fits

265,292

28

fastspec-iron-sv3-dark.fits

592,190

1,668

fastspec-iron.fits

17,995,820

64,943

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.

Note that the tagged dependencies can be retrieve from any FITS file with the following bit of code:

import fitsio
from desiutil.depend import Dependencies
codever = Dependencies(fitsio.read_header('/path/to/fastspecfit/file.fits, ext=0))
for codename, version in codever.items():
    print(codename, version)

Software Package

Version(s)

python

3.10.8

numpy

1.22.4

scipy

1.8.1

astropy

5.2.1

yaml

6.0

matplotlib

3.6.2

fitsio

1.1.8

desiutil

3.4.2

desispec

0.60.2

desitarget

2.7.0

desimodel

0.19.0

speclite

0.17

fastspecfit

2.5.0, 2.5.1

Environment Variable

Value

DESI_ROOT

/dvs_ro/cfs/cdirs/desi

DUST_DIR

/dvs_ro/cfs/cdirs/cosmo/data/dust/v0_1

FPHOTO_DIR

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

FTEMPLATES_DIR

/dvs_ro/cfs/cdirs/desi/science/gqp/templates/fastspecfit

FTEMPLATES_FILE

ftemplates-chabrier-1.3.0.fits (see README.txt)

FPHOTO_FILE

/global/common/software/desi/perlmutter/desiconda/20230111-2.1.0/code/fastspecfit/2.5.1/lib/python3.10/site-packages/fastspecfit/data/legacysurvey-dr9.yaml

EMLINES_FILE

/global/common/software/desi/perlmutter/desiconda/20230111-2.1.0/code/fastspecfit/2.5.1/lib/python3.10/site-packages/fastspecfit/data/emlines.ecsv

Notes & Known Issues

v2.1 (latest release)

  • Release date: January 2024

  • FastSpecFit version: 2.5.0, 2.5.1

  • 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).