Detailed Decomposition of Galaxy Images II: Fitting Spiral Arms, Bars, and Non-axisymmetric Structures in GALFIT 3.0

Details Detailed Decomposition of Galaxy Images II: Fitting Spiral Arms, Bars, and Non-axisymmetric Structures in GALFIT 3.0 Detailed Decomposition of Galaxy Images II: Fitting Spiral Arms, Bars, and Non-axisymmetric Structures in GALFIT 3.0

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.4704p&link_type=abstract

American Astronomical Society, AAS Meeting #211, #47.04; Bulletin of the American Astronomical Society, Vol. 39, p.804

Astronomy and Astrophysics

Astronomy

3

Scientific paper

The technique of fitting galaxy light profiles with analytic functions (e.g. de Vaucouleurs, exponential), also known as parametric fitting, has been a useful tool for studying galaxy structure and evolution. It is often used to quantify global properties of galaxies such as luminosity, size, ellipticity, and profile shape in a self-consistent manner. It also allows one to deblend multiple components of a galaxy, e.g. bulge/disk/bar/AGN, or to separate overlapping galaxies in a rigorous and robust way. However, the traditional method of fitting galaxies relies on using ellipsoid models, which is sometimes criticized to argue in favor of non-parametric techniques. In this study, we show that two dimensional image fitting is not fundamentally restricted to using axisymmetric ellipsoid shapes. By breaking from axisymmetry parametrically through the use of Fourier modes, one can better quantify the degree of galaxy irregularity in an intuitive and well-motivated manner. We also introduce a technique that allows one to fit spiral structures in late-type galaxies through the use of coordinate rotation. By comparing with more realistic models now possible, we find that the traditional use of simple ellipsoid models is robust even on irregular and spiral galaxies, because single component fits are by nature large scale averages. However, when it comes to quantifying sub-components of a galaxy, sometimes it is necessary to model structures in detail, such as when performing bulge-to-disk decomposition of galaxies with strong spiral arms, or quantifying the symmetry due to bright (e.g. bulge) and faint (e.g. disk) galaxy sub-components separately. These new techniques are implemented in GALFIT 3.0 (http://www.ociw.edu/ peng/work/galfit/galfit.html ).
CYP gratefully acknowledges support from the Plaskett Fellowship (NRC-HIA) and the Institute/Giacconi Fellowship (STScI) programs.

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