Quasar Spectral FITting package

QSFit is a software package to automatically perform spectral analysis of Active Galactic Nuclei (AGN) optical/UV spectra. It provides estimates of:

The main purpose of QSFit is to allow anyone to perform AGN spectral analysis in a simple, replicable and shareable way. The code is available on Github and can be easily customized for specific purposes.

Reference Paper

The paper was published on MNRAS, 72, 4, 4051-4080 (2017). Preprint available from arXiv.

If you make use of the catalog or the code, please unknowledge as: Calderone et al., MNRAS, 72, 4 (2017)

Catalog of spectral properties (ver. 1.2.4)

After the publication of the paper we found a few small bugs in the code affecting:
  • the freezing/thawing of the iron template component at optical wavelengths (this bug affected only the spectral estimates for the sources with z < 0.4);
  • the calculation of the spectral coverage of the emission lines (this bug affected only those source with many spectral channels whose quality mask is not zero, as marked by the SDSS reduction pipeline);
  • the spectral estimates of QSFit had a very weak dependence on the data type precision of the input keyword Z and EBV: changing them from FLOAT to DOUBLE would introduce slight discrepancies in the results.
We fixed all these bugs and generated a new QSFit catalog. The spectral estimates, in the vast majority of cases, are compatible with the previous ones (within the quoted uncertainties). The new catalog is available here and the new source code release can be downloaded here.
We used QSFit to analyze 71,251 optical spectra (from SDSS-DR10) of Type 1 AGN at z < 2, and compiled a catalog of spectral properties. See the reference paper.

The catalog can be explored online or downloaded as a FITS file.
The complete data analysis can be easily replicated by running QSFit (as shown in the example above) on all the spectra in the sample.

The old version 1.2 is available here.

Source Code (Github)

The source code can be downloaded from Github. The software is written in IDL and released under the GPL license. The prerequisites to run QSFit are IDL (ver. >= 8.1) and Gnuplot (ver. >= 5.0).

To run QSFit you should download and unzip the package from Github, then change to the directory where you unpacked the source code and start an IDL session. There is no need to change the IDL PATH system variable, QSFit provide a simple way to compile all the required procedures: simply call compile at the IDL prompt.

The QSFit package already comes with a SDSS DR-10 FITS file to test the code. The commands to run the analysis and plot the results are:
res = qsfit(’data/spec-0752-52251-0323.fits’, z=0.3806, ebv=0.06846)
qsfit_plot, res
Further informations may be found in Appendix B of the reference paper (arXiv).


Giorgio (giorgio.calderone@inaf.it)
Luciano (luciano.nicastro@inaf.it)

L. Nicastro & G. Calderone 2016 − 2018