MaNGA Firefly value-added catalog

The MaNGA FIREFLY VAC provides measurements of spatially resolved stellar population properties in MaNGA galaxies. It is built on and complements the products of the MaNGA data analysis pipeline (DAP, Westfall et al. in prep) by providing higher-order and model-based data products. 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 using the supercomputer Sciama2 at Portsmouth University. The VAC is a single fits file (7 GB) containing measurements for 4675 MaNGA galaxies in DR15. The catalogue contains basic galaxy information (e.g., galaxy ID, galaxy mass), global parameters (e.g., central age), gradient parameters (e.g., age gradient) and spatially resolved quantities (e.g., 2-D age maps). These various categories are described in detail below. The catalogue should be referenced through Goddard et al. 2017 and Parikh et al. 2018.

Information regarding the catalogue can be found from the following links:

• MANGA firefly SAS folder containing:
  •  manga_firefly-v2_4_3.fits - full catalogue, downloadable fits-format file, ~6.9 GB
  • manga-firefly-v2_4_3-GLOBALPROP.fits  - minimal data table only including global properties and gradients (HDU1-3), downloadable fits-format file, ~1 MB
  • manga-firefly-v2_4_3-STELLARPOP.fits  - medium sized data table only including maps of stellar population parameters (HDU1-13), downloadable fits-format file, ~2.5 GB
  • manga-firefly-v2_4_3-INDICES.fits  - large data table only including maps of stellar absorption indices (HDU1-6, 14-41), downloadable fits-format file, ~4.7 GB
• MANGA FIREFLY VAC datamodel
• mangaFirefly CAS Table

Each object in the catalogue is characterised by the MaNGA identifier, MaNGA plate and IFU numbers, and coordinates (right ascension, declination). The catalogue further provides redshift, stellar mass (from the NSA catalogue), and version numbers of the DRP, DAP and FIREFLY runs used to produce and analyse the data. This information is found in the header HDU1.
Other basic galaxy information used in the MaNGA VAC, e.g. the effective radii (R_e) values, the axis ratios and position angles used to assign R_e fractions to x- and y-positions on the sky are adopted from the NSA catalogue and are available through the MaNGA DRPall file. The kinematics (stellar velocities and velocity dispersions) used to derive the properties in this VAC are available from the MaNGA Data Analysis Pipeline (DAP).

Light-weighted and mass-weighted stellar population ages (log(age/Gyr)) and metallicities ([Z/H]) are provided with 1-sigma errors for a central 3 arcsec aperture and for an elliptical shell at 1 effective radius R_e (obtained from Voronoi binning, see below). Stellar population age and metallicity are obtained from full spectral fitting using the code FIREFLY as described below. This information is found in the header HDU2.

In addition to the global parameters, gradients in light-weighted and mass-weighted age and metallicity are provided. The gradients are characterised through zero point and slope and their errors. The gradient is measured linear in radius within 1.5 R_e with units dex/R_e via Maximum Likelihood Estimation by fitting a linear model to the stellar population properties derived on each Voronoi bin of the 2-dimensional map (see below). Errors are obtained using an Monte-Carlo Markov Chain sampler. This information is found in the header HDU3.

Finally, the catalogue provides the spatially resolved measurements of a number of stellar population indicators in 2-dimensional maps. These stellar population indicators included are absorption line-strength indices directly measured on the spectra, as well as the stellar population parameters age, metallicity, stellar mass and dust attenuation E(B-V) derived from full spectral fitting with the code FIREFLY. This information is in the headers HDU4-40.
The 2-dimensional maps are created by the MaNGA DAP (Westfall et al, in preparation) through Voronoi binning using the algorithm of Cappellari & Copin 2003. Individual MaNGA spectra for each galaxy were binned to create cells with a minimum signal-to-noise ratio of 10 per pixel. This threshold was chosen as the optimum compromise between quality of the spectra and spatial resolution (Goddard et al. 2017).
Spatial information (HDU4, HDU5, HDU13):
The bin number, x position (arcsec), y position (arcsec) and radius (in R_e) of each cell of the 2-dimensional maps are provided in HDU4. The geometry of the IFU is given in HDU5. The corresponding S/N ratios (per pixel within r-band) are in HDU13.
Stellar population parameters (HDU6-12):
The light-weighted and mass-weighted stellar ages (log age/Gyr) and metallicities (dex), E(B-V) (mag), mass (log M/M_sun) and surface mass density (log M/M_sun/kpc²) with associated errors for each spatial bin are provided in HDU6-12.
Absorption line-strengths (HDU14-41):
Measurements of the 25 Lick absorption-line indices (Trager et al. 1998; Worthey & Ottaviani 1997), as well as CaHK (Serven, Worthey & Briley 2005) and D4000, Dn4000 (Bruzual 1983; Balogh et al. 1999) are included. Errors on the measurements were obtained through Monte Carlo simulations. The features are measured on rest-frame, emission-line free spectra produced by the MaNGA DAP. The emission line spectra are determined by the DAP (Westfall et al, in preparation) using an adapted version of the pPXF code of Cappellari & Emsellem 2004. The absorption index measurements provided in this VAC were then corrected for velocity dispersion broadening (adopted from the DAP). The effect was determined on best-fit model spectra. The measurement is therefore provided at the spectral resolution of the MaNGA spectra. The correction factor is provided in addition, so that the original, uncorrected measurement can be reconstructed by dividing the catalogue value by the correction factor. The correction is multiplicative for all indices except for the higher-order Balmer indices (Hgamma, Hdelta) where it is additive. The correction is negligible for the bandhead indices (D4000, Dn4000, CN1, CN2, Mg2, TiO1, TiO2). This information is provided in HDU13-40.

The stellar population parameters age, metallicity, mass, and dust attenuation are determined through the full spectral fitting code FIREFLY (Wilkinson et al. 2015; Wilkinson et al. 2017). FIREFLY is a chi-squared minimisation fitting code that for a given input spectral energy distribution compares combinations of single-burst stellar population models, following an iterative best-fitting process until convergence is achieved. The weight of each component can be arbitrary and no regularisation or additional prior than the adopted model grid is applied. Dust attenuation is added in a novel way, using a High-Pass Filter in order to rectify the continuum before fitting. The returned attenuation array is then matched to known analytical approximations to return an E(B-V) value. This procedure allows for removal of large scale modes of the spectrum associated with dust and/or poor flux calibration. FIREFLY derives full star formation histories and provides light- and mass-weighted stellar population properties (age and metallicity), E(B-V) values and stellar mass for the most likely best fitting model. Light-weighted properties involve weighting each stellar population component by their geometrically averaged total luminosity across the wavelength range, whereas mass-weighted properties involve weighting by the stellar mass contribution over the wavelength range. Errors on these properties are obtained by the likelihood of solutions within the statistical cut (of order 100-1000). In this VAC the input stellar population models of Maraston & Stromback 2011 are used, based on the MILES stellar library, with Kroupa IMF ( Kroupa 2001).
Rest-framed, emission-line free spectra and velocity dispersions are needed as input to the FIREFLY code. Both the kinematics (velocities and velocity dispersions) and the emission-line spectra are determined by the DAP (Westfall et al., in preparation) using an adapted version of the pPXF code by Cappellari & Emsellem 2004.
Each spectrum was then fit with FIREFLY over the wavelength range 3600-7500A, with a grid of metallicities spanning -2.3 < [Z/H] < 0.3 and ages spanning 0.0065 < Age(Gyr) < 15.0. Example fits to binned spectra and stellar populations maps are shown below:

Note: For technical details regarding the code, see the aforementioned papers. The source code is available through the SDSS svn. There is a publicly available Firefly fitter (v1_1_0) code which depends on a set of publicly available stellar population (v1_0_2) models.

We have written a small python script (available on github here) as an example of how to plot maps from the MaNGA FIREFLY VAC. The fits file of the VAC should be downloaded and by default placed in the same directory as this script. The script should then run directly by typing python plot_maps.py on the commandline. The script plots the map of one property of a single galaxy, and can be adapted to plot other properties and galaxies.

Primary References

Goddard et al. 2017, MNRAS, 466, 4731

Parikh et al. 2018, MNRAS, 477, 3954

Other Related References

FIREFLY home page

Wilkinson et al. 2015, MNRAS, 449, 328

Maraston & Stromback, 2011, MNRAS, 418, 2785

Wilkinson et al 2017, MNRAS, 472, 4297

Westfall et al. in preparation

Cappellari & Copin 2003, MNRAS, 342, 345

Cappellari & Emsellem, 2004. 1999, pasp, 116, 118