Survey design for Spectral Energy Distribution fitting: a Fisher Matrix approach

TL;DR

This paper evaluates the Fisher Matrix approach for optimizing galaxy spectral energy distribution surveys, comparing its predictions to more detailed PDF fitting methods using simulated and real data.

Contribution

It demonstrates that the Fisher Matrix provides reliable uncertainty estimates within a factor of two for most cases, validating its use in survey design.

Findings

Fisher Matrix uncertainties agree with PDF methods within a factor of two in ~90% of cases.

Inclusion of age priors improves Fisher Matrix accuracy.

Fisher Matrix is a useful and efficient tool for survey planning.

Abstract

The spectral energy distribution (SED) of a galaxy contains information on the galaxy's physical properties, and multi-wavelength observations are needed in order to measure these properties via SED fitting. In planning these surveys, optimization of the resources is essential. The Fisher Matrix formalism can be used to quickly determine the best possible experimental setup to achieve the desired constraints on the SED fitting parameters. However, because it relies on the assumption of a Gaussian likelihood function, it is in general less accurate than other slower techniques that reconstruct the probability distribution function (PDF) from the direct comparison between models and data. We compare the uncertainties on SED fitting parameters predicted by the Fisher Matrix to the ones obtained using the more thorough PDF fitting techniques. We use both simulated spectra and real data, and consider a large variety of target galaxies differing in redshift, mass, age, star formation history, dust content, and wavelength coverage. We find that the uncertainties reported by the two methods agree within a factor of two in the vast majority (~ 90%) of cases. If the age determination is uncertain, the top-hat prior in age used in PDF fitting to prevent each galaxy from being older than the Universe needs to be incorporated in the Fisher Matrix, at least approximately, before the two methods can be properly compared. We conclude that the Fisher Matrix is a useful tool for astronomical survey design.