cigale

CIGALE, short for Code Investigating GALaxy Emission, is an open-source software package designed to model the spectral energy distribution (SED) of galaxies from the ultraviolet to the infrared. It operates under the principle of energy balance, ensuring that the energy absorbed by dust in the UV/optical is re-emitted in the infrared. The code is widely used in extragalactic astronomy to interpret multiwavelength data and to derive physical properties of galaxies.

CIGALE works in a modular fashion, allowing users to assemble SEDs from components that describe a galaxy’s star formation history, stellar populations, dust attenuation, dust emission, and, when relevant, an active galactic nucleus (AGN) contribution. Typical modules include options for different star formation histories, population synthesis libraries, attenuation laws, and collections of dust emission templates. By combining these modules, CIGALE generates a library of model SEDs and compares them to observed photometry or spectroscopy across multiple bands.

The fitting process is Bayesian in nature. CIGALE computes likelihoods for model parameter combinations and derives posterior probability distributions for physical properties such as star formation rate, stellar mass, dust luminosity, attenuation, and, if included, the strength of AGN emission. Output products usually include best-fit SEDs, parameter estimates with uncertainties, and diagnostic plots or logs for quality assessment.

CIGALE is cross-platform and programmable in Python, with a command-line interface and an API for integration into analysis pipelines. It is maintained with ongoing updates and extensive documentation, and it is widely cited in studies of galaxy evolution for its flexible treatment of energy balance and modular approach to SED fitting.