GALFIT Home Page

Above: Simultaneous model fit of 5 galaxies (Left: original data, Middle: GALFIT model, Right: residual.)

Animation: GALFIT takes away the subcomponents of NGC 4111 layer by layer.

GALFIT on Facebook page for updates, questions, and discussions.

1. Download:
   • Email to GALFIT users
   • The most recent version of GALFIT (version 3.0.5, April 23, 2013), in binary form.

     (Due to the use of several copyrighted algorithms embedded in GALFIT, the source code itself currently cannot be made publicly available. When I have more free time to thoroughly test out replacement algorithms, I will replace the relevant copyright codes to make the GALFIT source available again. In the meanwhile, I can distribute the binary code, which is both good and bad. Good: you don't have to compile the code yourself. Bad: the operating systems below represent only those to which I have access. Contact me if yours is not in one of them and we'll find a solution.)

     Redhat/Enterprise 64	Debian/Ubuntu 32	Mac OS X (Mavericks)
     Debian/Ubuntu 64	Mac OS X (pre-Mavericks)

   • An Example Tar File -- Try out GALFIT on this first
   • Original paper on GALFIT (Peng et al. 2002, Astronomical Journal (AJ), 124, 266)
   • Paper on new GALFIT Version 3.0 (Peng et al. 2010, Astronomical Journal (AJ), 139, 2097)
   • Instructions on using GALFIT
   • Keynote presentation for the Jan. 2010 AAS High-z Galaxy Morphology Special Session
   • Sample input files:

     NOTA BENE: The input file has changed between Version 3 and Version 2. Parameters 8, 9, and 10 in Version 2 are now called 9, 10, and C0 in Version 3. C0 is now an optional parameter, so it is only visible when specified explicitly and given a value.

     Bare bones (Version 3.0+)
     All possible function types (Version 3.0+)
     Constraints file
     

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2. Please Read Advisory on using GALFIT and Top 10 Rules of Thumb before fitting.

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3. GALFIT in action: Examples on...
   • Automated batch fitting of distant galaxies.
   • Manual, detailed, fitting of nearby galaxies.
   • Fitting irregular and spiral galaxies (Version 3.0).

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4. Frequently Asked General Questions (FAQ) and Other General Information:
   • What is GALFIT?
   • How is GALFIT different from GIM2D?
   • What are the limitations of GALFIT?
   • How fast is GALFIT?
   • Are 1-D algorithms better than 2-D at fitting peculiar galaxies or low surface brightness regions?
   • Are 1-D algorithms more robust against neighboring contamination than 2-D fitting techniques?
   • Are you going to automate GALFIT for batch fitting of galaxies?
   • Should I fit spiral arms or higher order modes?
   • Do you provide user support for GALFIT?
   • Can you inform me when there are updates to GALFIT?
   • Disclaimers, User Agreement and Copyrights
   • Acknowledgments

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5. Frequently Asked Technical Questions (FAQ):
   • Top 10 Rules of Thumb for Galaxy Fitting. (← Please read this. Important.)
   • Why must my data be in counts instead of counts/sec for GALFIT to generate the correct sigma image? (← Please read.)
   • What happens if you provide GALFIT an image with the wrong units for generating the sigma image? (← Please read.)
   • How do I determine the initial parameters?
   • Why is the GALFIT output image blank?
   • How do I mask out image regions from the fit?
   • How biased are the size and luminosity measurements by low signal-to-noise when you can't see outer regions of galaxies?
   • Why determine galaxy sizes and luminosities with parametric instead of non-parametric techniques?
   • How do I measure the half-light radius (r_e) for a multi-component galaxy, or when the residuals don't look smooth?
   • What would cause systematic errors in fitting? (← Please read. Important.)
   • Are 1-D algorithms better than 2-D at fitting peculiar galaxies or low surface brightness regions?
   • Are 1-D algorithms more robust against neighboring contamination than 2-D fitting techniques?
   • Why are the fit parameters so sensitive to the sky value and/or neighboring galaxies?
   • Everything you want to know about the sigma (σ) image and how GALFIT calculates χ_ν².
   • Is it sometimes better to use uniform (or another non-Poisson) weighting scheme in the fit?
   • What fitting box size should I use?
   • What convolution box size should I use?
   • How do I create a point spread function (PSF) for convolution?
   • What PSF size should I use?
   • How do I fit or interpret the Fourier modes?
   • How do I fit spiral structures?
   • Why can't I fit for the total luminosity for truncation models?
   • How do I obtain the total luminosity for truncation models?
   • Why are the uncertainties quoted in ``fit.log'' sometimes so small?
   • Why does the GALFIT iteration, i.e. ``count-down'', clock keep bouncing up and down?
   • Why does IRAF display give "ERROR: FXF: inherit not permitted when PHU has NAXIS != 0"?

ACKNOWLEDGMENTS

Chien Peng ()