MAGPHYS

MAGPHYS (Multi-wavelength Analysis of Galaxy Physical Properties) is a public code and model framework for deriving the physical properties of galaxies by fitting their panchromatic spectral energy distributions from the ultraviolet to the far-infrared. It is designed to provide coherent estimates of stellar masses, star formation rates, dust properties, and related quantities through energy-balance between absorbed starlight and re-emitted dust emission.

MAGPHYS operates by comparing observed photometry to a large library of precomputed model SEDs that span a wide range of star formation histories, metallicities, and dust contents. The stellar emission is generated with stellar population synthesis models, while infrared dust emission is described by a two-component dust framework. A key feature is the energy-balance constraint: the energy absorbed by dust in the UV/optical must be carried by the infrared emission, ensuring consistency between attenuation and emission.

Fitting is performed within a Bayesian framework, producing posterior probability distributions for physical parameters. Typical outputs include stellar mass, instantaneous and average star formation rate, total dust luminosity, dust mass, attenuation in different bands, and rest-frame magnitudes. MAGPHYS is widely used for multiwavelength galaxy surveys and has been applied to data from facilities such as GALEX, SDSS, Spitzer, and Herschel.

Limitations and scope: MAGPHYS assumes a balanced dust emission and relies on a particular dust model and stellar-population libraries, which may not capture all complexities of every galaxy type. It is best suited for star-forming and normal galaxies with good UV-to-FIR coverage and may be less reliable for AGN-dominated systems or sparse data. The code was introduced by da Cunha, Charlot, and Elbaz in 2008 and has become a standard tool in extragalactic astrophysics.