References and related software

The references below are grouped by the modelling components that appear in qsospec: global continuum, Balmer continuum, Fe II pseudo-continuum, broad-line profiles, line-complex recipes, and host-galaxy decomposition.

This list is not intended to be exhaustive. It highlights references that are most relevant for the modelling choices implemented in qsospec.

Method references

General quasar spectra and spectral components

• Francis et al. (1991), 1991ApJ…373..465F — early quasar composite spectrum and line measurements.

• Boroson & Green (1992), 1992ApJS…80..109B — optical quasar spectral measurements, Eigenvector 1, and the classic I Zw 1-based optical Fe II template context.

• Elvis et al. (1994), 1994ApJS…95….1E — multiwavelength quasar spectral energy distributions.

• Vanden Berk et al. (2001), 2001AJ….122..549V — SDSS quasar composite spectrum.

• Richards et al. (2006), 2006ApJS..166..470R — quasar spectral energy distributions from optical to mid-infrared data.

• Shang et al. (2011), 2011ApJS..196….2S — quasar SED atlas and continuum diversity.

• Krawczyk et al. (2013), 2013ApJS..206….4K — large-sample quasar spectral energy distributions.

• Euclid Collaboration: Lusso et al. (2024), 2024A&A…685A.108E — Euclid preparation study of active-galactic-nucleus spectroscopy with the NISP slitless spectroscopic mode.

• Euclid Collaboration: Fu et al. (2025), 2025arXiv251208803E — Euclid quasar spectroscopy paper using early Euclid/NISP spectra, relevant for quasar identification, redshift measurement, and composite-spectrum work.

Balmer continuum and high-order Balmer lines

• Grandi (1982), 1982ApJ…255…25G — classic AGN small-blue-bump / Balmer-continuum treatment.

• Wills, Netzer & Wills (1985), 1985ApJ…288…94W — Fe II, Balmer continuum, and small-blue-bump modelling in quasars.

• Storey & Hummer (1995), 1995MNRAS.272…41S — hydrogen recombination line intensities, useful for high-order Balmer series templates.

• Dietrich et al. (2002), 2002ApJ…581..912D — broad-line and continuum measurements including UV/optical quasar spectral components.

• Kovacevic, Popovic & Kollatschny (2014), 2014AdSpR..53.1414K — Balmer pseudocontinuum model for type 1 AGN spectra.

• Calderone et al. (2017), 2017MNRAS.472.4051C — QSFit; includes automatic Balmer-continuum, iron, host, continuum, and emission-line fitting.

Iron templates and Fe II pseudo-continuum

• Boroson & Green (1992), 1992ApJS…80..109B — commonly used optical Fe II template context from I Zw 1.

• Vestergaard & Wilkes (2001), 2001ApJS..134….1V — empirical UV Fe II/Fe III template from I Zw 1.

• Veron-Cetty, Joly & Veron (2004), 2004A&A…417..515V — detailed I Zw 1 optical emission-line spectrum and Fe II template information.

• Tsuzuki et al. (2006), 2006ApJ…650…57T — UV Fe II template treatment around Mg II.

• Kovacevic, Popovic & Dimitrijevic (2010), 2010ApJS..189…15K — optical Fe II template with grouped multiplet components.

• Garcia-Rissmann et al. (2012), 2012ApJ…751….7G — near-infrared Fe II template derived from I Zw 1.

• Park et al. (2022), 2022ApJS..258…38P — modern empirical optical Fe II template for the H beta region.

• Kovacevic et al. (2025), 2025A&A…694A.289K — comparison of optical Fe II templates and their impact on AGN spectral fitting.

Broad-line profiles, components, and virial measurements

• Sulentic et al. (2000), 2000ARA&A..38..521S — review of quasar Eigenvector 1 and broad-line diversity.

• Vestergaard & Peterson (2006), 2006ApJ…641..689V — single-epoch black-hole mass scaling relations.

• Hu et al. (2008), 2008ApJ…683L.115H — evidence for intermediate-line and very-broad H beta components.

• Zamfir, Sulentic & Marziani (2010), 2010MNRAS.403.1759Z — H beta profile shapes and Population A/B quasar line-profile behaviour.

• Denney (2012), 2012ApJ…759…44D — issues in using C IV for black-hole mass estimates.

• Kollatschny & Zetzl (2013), 2013A&A…549A.100K — Lorentzian-like broad-line profiles, turbulence, and rotational broadening.

• Marziani et al. (2013), 2013A&A…555A..89M — comparison of Mg II and H beta as virial broadening estimators.

• Coatman et al. (2017), 2017MNRAS.465.2120C — C IV blueshift correction and implications for black-hole masses.

Reddening and extinction

• Schlegel, Finkbeiner & Davis (1998), 1998ApJ…500..525S — all-sky Galactic dust reddening map.

• Schlafly & Finkbeiner (2011), 2011ApJ…737..103S — recalibration applied to SFD E(B-V) values.

• Cardelli, Clayton & Mathis (1989), 1989ApJ…345..245C — widely used Galactic extinction law.

• Fitzpatrick (1999), 1999PASP..111…63F — updated Milky Way extinction curve.

• Planck Collaboration (2016), 2016A&A…594A..11P — GNILC thermal-dust map used by the default foreground correction.

• Calzetti et al. (2000), 2000ApJ…533..682C — starburst attenuation curve, often used as a comparison law.

Near-infrared AGN lines

• Rodriguez-Ardila et al. (2002), 2002ApJ…565..140R — near-infrared spectroscopy of Seyfert galaxies and NIR emission-line diagnostics.

• Landt et al. (2008), 2008ApJS..174..282L — near-infrared spectra of AGN and quasar line measurements.

• Garcia-Rissmann et al. (2012), 2012ApJ…751….7G — near-infrared Fe II template derived from I Zw 1.

• Euclid Collaboration: Lusso et al. (2024), 2024A&A…685A.108E — Euclid preparation study of active-galactic-nucleus spectroscopy with the NISP slitless spectroscopic mode.

• Euclid Collaboration: Fu et al. (2025), 2025arXiv251208803E — Euclid quasar spectroscopy paper using early Euclid/NISP spectra, relevant for quasar identification, redshift measurement, and composite-spectrum work.

Emission-line physics and diagnostics

• Osterbrock & Ferland (2006), 2006agna.book…..O — standard reference for AGN emission-line physics and nebular diagnostics.

Emission-line fitting, catalogues, and automated pipelines

• Shen et al. (2011), 2011ApJS..194…45S — SDSS DR7 quasar properties catalogue with spectral measurements.

• Calderone et al. (2017), 2017MNRAS.472.4051C — QSFit automatic optical AGN spectral fitting.

• Shen et al. (2019), 2019ApJS..241…34S — quasar spectral measurements and PyQSOFit-related reference.

• Sexton et al. (2021), 2021MNRAS.500.2871S — BADASS; Bayesian AGN Decomposition Analysis for SDSS Spectra.

AGN-host decomposition and stellar-continuum fitting

• Yip et al. (2004), 2004AJ….128.2603Y — SDSS quasar eigenspectra and PCA decomposition.

• Vanden Berk et al. (2006), 2006AJ….131…84V — spectral decomposition of broad-line AGN and host galaxies.

• Bruzual & Charlot (2003), 2003MNRAS.344.1000B — stellar population synthesis models widely used for host-galaxy modelling.

• Cappellari & Emsellem (2004), 2004PASP..116..138C — original pPXF method.

• Vazdekis et al. (2016), 2016MNRAS.463.3409V — E-MILES stellar population models.

• Cappellari (2017), 2017MNRAS.466..798C — pPXF updates and full-spectrum fitting.

• Cappellari (2023), 2023MNRAS.526.3273C — pPXF full-spectrum plus photometric fitting and non-parametric star formation histories.

• Ren et al. (2024), 2024arXiv240617598R — prior-informed AGN-host spectral decomposition using PyQSOFit.

Related software

Quasar/AGN spectral-fitting packages

• PyQSOFit — Python quasar spectral-fitting package derived from Yue Shen’s IDL fitting code; includes continuum, Fe II templates, line-fitting parameter tables, host templates, and uncertainty estimation. See also Guo et al. (2018) and Shen et al. (2019).

• qsofitmore — extended PyQSOFit-family package for UV–optical quasar spectra, DESI/LAMOST use cases, Fe II/Balmer updates, and host-decomposition experiments; described in Fu et al. (2022), 2022ApJS..261…32F.

• QSFit — IDL-based automatic optical AGN spectral-fitting code; simultaneously fits the global AGN continuum, Balmer continuum, Fe II complexes, host galaxy, and emission lines. See Calderone et al. (2017).

• QSFit.jl — Julia reimplementation of QSFit with a native interactive GUI (online demo).

• BADASS3 — Bayesian AGN Decomposition Analysis for SDSS Spectra; Python-based simultaneous AGN/host/line fitting with MCMC-oriented uncertainty estimation. See Sexton et al. (2021).

• FastSpecFit — DESI-oriented fast spectral synthesis and emission-line fitting. See Moustakas et al. (2023).

• SHEAP — JAX/GPU-based AGN spectral-fitting framework described by Avila-Vera et al. (2026); continuum, host, Fe II, and multi-component emission-line fitting. A public repository link was not identified at the time this list was prepared; replace this link with the official repository if/when available.

Host-galaxy and stellar-continuum fitting

• pPXF — penalized pixel-fitting code for stellar and gas kinematics, stellar populations, and full-spectrum fitting.

Template and line-list resources

• Park optical Fe II template — optical Fe II template for the H beta region from Park et al. (2022).

General astronomy/spectrum infrastructure

• Astropy — core astronomy package for units, tables, FITS I/O, coordinates, and modelling utilities.

• specutils — Astropy-affiliated package for astronomical spectra.

• speclite — lightweight spectral utilities used in DESI-related workflows.

• lmfit — non-linear least-squares modelling interface built on SciPy optimizers.

• emcee — affine-invariant MCMC sampler often used for astronomical uncertainty estimation.