firefly (Fitting IteRativEly For Likelihood analYsis): a full spectral fitting code

Abstract

We present a new spectral fitting code, FIREFLY, for deriving the stellar population properties of stellar systems. FIREFLY is a chi-squared minimisation fitting code that fits combinations of single-burst stellar population models to spectroscopic data, following an iterative bestfitting process controlled by the Bayesian Information Criterion. No priors are applied, rather all solutions within a statistical cut are retained with their weight. Moreover, no additive or multiplicative polynomia are employed to adjust the spectral shape. This fitting freedom is envisaged in order to map out the effect of intrinsic spectral energy distribution (SED) degeneracies, such as age, metallicity, dust reddening on galaxy properties, and to quantify the effect of varying input model components on such properties. Dust attenuation is included using a new procedure, which was tested on Integral Field Spectroscopic (IFS) data in a previous paper. The fitting method is extensively tested with a comprehensive suite of mock galaxies, real galaxies from the Sloan Digital Sky Survey and Milky Way globular clusters. We also assess the robustness of the derived properties as a function of signal-to-noise ratio and adopted wavelength range. We show that FIREFLY is able to recover age, metallicity, stellar mass and even the star formation history remarkably well down to a S/N ∼ 5, for moderately dusty systems. Code and results are publicly available at WWW.ICG.PORT.AC.UK/FIREFLY.

Signatures of Stellar Accretion in MaNGA Early-type Galaxies

“…The library spans the wavelength range 4000Å to 7400Å. As shown in Wilkinson et al 2017, FIREFLY effectively recovers stellar population parameters for spectra with S/N> 10 (see also Goddard et al 2017b). To limit the systematics in the measurements from Firefly, we excluded any co-added spectra with S/N< 10.…”

The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the Extended Baryon Oscillation Spectroscopic Survey and from the Second Phase of the Apache Point Observatory Galactic Evolution Experiment

“…We perform full spectral fitting on individual spectra, making use of high spectral resolution stellar population models published in Wilkinson et al (2017). Calculations are carried out for several choices of the model input, including three stellar initial mass functions and three input stellar libraries to the models.…”

“…These are measurements of optical absorption line strengths as well as the physical properties age, metallicity, and dust attenuation. The latter are derived from full spectral fitting with the code FIREFLY (Wilkinson et al 2015(Wilkinson et al , 2017 using the supercomputer SCIAMA2 at Portsmouth University. The VAC is a single FITS file (4 GB) containing measurements of all DR14 MaNGA galaxies.…”

The SLUGGS survey: measuring globular cluster ages using both photometry and spectroscopy

“…Our technique could be easily extended to use a more sophisticated age-metallicity (and possibly chemistry) prior from full spectral fitting (e.g. Koleva et al 2008;Larsen et al 2017;Wilkinson et al 2017;Conroy et al 2018) or even by simultaneously fitting both photometry and spectroscopy to fully utilise the information contained in the spectroscopy (Leja et al 2017). A previous example of combining the stellar population constraints from optical photometry and spectroscopy can be found in Gu et al (2018) who used both to place stronger constraints on the old ages of three ultra-diffuse galaxies.…”