Accepted for publication in Astrophysics & Space Science, 2010.
astro-ph/1008.0395

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FITTING THE INTEGRATED SPECTRAL ENERGY DISTRIBUTIONS OF GALAXIES

Jakob Walcher 1, Brent Groves 2, Tamás Budavári 3, Daniel Dale 4


1 Research and Scientific Support Department, European Space Agency, Keplerlaan 1, 2200AG Noordwijk, The Netherlands jwalcher@rssd.esa.int
2 Sterrewacht Leiden, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands
3 Dept. of Physics and Astronomy, The Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
4 Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA


Abstract. Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting, with a special emphasis on describing the interplay between the quality of the available data, the quality of the available models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties. We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift, stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details of dust properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The present review will be made available on an interactive, moderated web page (sedfitting.org), where the community can access and change the text. The intention is to expand the text and keep it up to date over the coming years.


Keywords: methods: data analysis, radiation mechanisms: general, techniques: photometric, techniques: spectroscopic, galaxies: ISM, galaxies: stellar content


Table of Contents

INTRODUCTION

MODELLING GALAXY SEDs
Stars
The ISM around the stars
Evolution of Galaxies

CONSTRUCTING OBSERVED GALAXY SEDs
Spectral response curve and resolution
Spatial resolution, aperture bias and matching
Examples of multi-wavelength datasets

METHODS AND VALIDATION OF SED FITTING
Parametrizing SED models
Spectral indices
Principal Component Analysis
Spectral fitting by inversion
Bayesian inference
Method-independent caveats

RESULTS OF SED FITTING: PHOTOMETRIC REDSHIFTS
Methods
Calibration and error budgets
A unified framework
The State of Photometric Redshifts

RESULTS OF SED FITTING: PHYSICAL PROPERTIES
Stars
Dust
Fitting the full UV to FIR SED

CONCLUSIONS

REFERENCES

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