IMFIT: A FAST, FLEXIBLE NEW PROGRAM FOR ASTRONOMICAL IMAGE FITTING

Journal Article · Sun Feb 01 00:00:00 EST 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/799/2/226· OSTI ID:22364311

Erwin, Peter ^[1]

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1. Max-Planck-Insitut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, GermanyAND (Germany)

I describe a new, open-source astronomical image-fitting program called IMFIT, specialized for galaxies but potentially useful for other sources, which is fast, flexible, and highly extensible. A key characteristic of the program is an object-oriented design that allows new types of image components (two-dimensional surface-brightness functions) to be easily written and added to the program. Image functions provided with IMFIT include the usual suspects for galaxy decompositions (Sérsic, exponential, Gaussian), along with Core-Sérsic and broken-exponential profiles, elliptical rings, and three components that perform line-of-sight integration through three-dimensional luminosity-density models of disks and rings seen at arbitrary inclinations. Available minimization algorithms include Levenberg-Marquardt, Nelder-Mead simplex, and Differential Evolution, allowing trade-offs between speed and decreased sensitivity to local minima in the fit landscape. Minimization can be done using the standard χ{sup 2} statistic (using either data or model values to estimate per-pixel Gaussian errors, or else user-supplied error images) or Poisson-based maximum-likelihood statistics; the latter approach is particularly appropriate for cases of Poisson data in the low-count regime. I show that fitting low-signal-to-noise ratio galaxy images using χ{sup 2} minimization and individual-pixel Gaussian uncertainties can lead to significant biases in fitted parameter values, which are avoided if a Poisson-based statistic is used; this is true even when Gaussian read noise is present.

• OSTI ID: 22364311
• Journal Information: Astrophysical Journal, Vol. 799, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ALGORITHMS
AVAILABILITY
BRIGHTNESS
DATA ANALYSIS
GALACTIC EVOLUTION
GALAXIES
IMAGE PROCESSING
IMAGES
LUMINOSITY
MAXIMUM-LIKELIHOOD FIT
MINIMIZATION
NOISE
PHOTOMETRY
POTENTIALS
SENSITIVITY
SIGNAL-TO-NOISE RATIO
THREE-DIMENSIONAL CALCULATIONS
TWO-DIMENSIONAL CALCULATIONS