eBOSS Firefly Value-Added Catalog

What stars populate galaxies is a generic question in galaxy evolution. The main stream method to infer stellar properties is spectral energy distribution fitting. There exist many variants of this method.
Variations occurs in all dimensions of the problem: the models of the stellar population, the wavelength covered by observations or by models, the fitting routine to compare model and data.

Summary

We measured galaxy properties of all SDSS, BOSS and eBOSS spectra with the FIREFLY fitting routine combined with the Maraston et al. (2011) models, see here for a description of the algorithm.
The number of galaxies with their stellar properties (age, metallicity, mass) characterized is nearly double of what was published in previous VACs. For the fit, we consider spectra that have a positive definite redshift (Z>Z_ERR>0) and CLASS==”GALAXY”. For each galaxy, we fit the stellar population parameters in nine different settings of stellar library and stellar initial mass function (IMF). We consider three IMFs: Chabrier, Kroupa and Salpeter, and three libraries: MILES, ELODIE, STELIB. The VAC paper, Comparat et al. 2017 documents the details of the runs and the results obtained. Please cite this paper if you use this VAC in a scientific publication.

Products

In this VAC, we provide three products. All are available here :

  1. A general catalog that contains the measured properties.
    • It is available in the CAS here and on the SAS here (4.3G).
    • Please consult the data model of the general catalog.
    • A version of this general catalog limited to SDSS data is here (1.4G).
    • A version of this general catalog limited to BOSS+eBOSS data is here (2.9G).
  2. For each unique plate-mjd combination, we merged the FIREFLY results with the specObjAll information into a (small) catalog.
    • We call them spFlyPlate fits files, see here an example on plate 3587, mjd 55182.
    • In these catalogs, you have access to the full star formation history fitted (not present in the general catalogs above).
    • For each of these files, we created a summary plot, see here for plate 3587, mjd 55182. It shows distributions of measured stellar ages and masses.
  3. For each galaxy spectrum considered, we created a fits file with the best fit models for each of the 9 imf x library combinations. We call them spFly fits files. It is a model of the continuum of the galaxy.
    • The spFly files are accessible here for SDSS and here for eBOSS. Files are grouped per plate number.
    • For each spectrum considered we created an image showing the spectrum, the models and some of the parameters deduced, see here for example plate:3587, mjd:55182, fiberid:0001. In each plate directory containing the spFly model files, you will find an ‘images’ directory that contains the images corresponding to this plate.
    • CAVEAT: A bug was found in the individual spFly files present on the SDSS server: the data extensions of the hdus 1 to 9 of the spFly files contain corrupted wavelength values. The FIREFLY team apologizes for any confusion this may have caused. As all original files were deleted, the team is currently re-generating these files: the SDSS data model compliant files should be available in 2018. Meanwhile, we opened access to the spFly files of this new run: you can access the original outputs of the latest run here.
  4. Alternative catalogs can be made upon request. For example we created full catalogs for each IMF – LIBRARY combination, they are available here and here. Such catalogs if proven useful might make it to the next data release, DR16.

Example of a spectral fit, figure taken from <a target="_blank" href="https://arxiv.org/abs/1711.06575">Comparat et al. 2017</a>
Example of a spectral fit, figure taken from Comparat et al. 2017

References and Links