The MegaMorph project has produced new versions of
GALFIT and GALAPAGOS
with several novel developments. The most significant,
and well-tested, of these is the implementation of
multi-band fitting. This enables a single, consistent,
wavelength-dependent model to be fit to any collection of
pixel registered images. We have also included an experimental method
for including a non-parametric component in the fit,
which can help improve the robustness of fits against the
effects of features such as spiral arms, bars, nuclear
sources, and un-masked neighbours. Finally, we have added
the ability to use MultiNest sampling as an alternative
to Levenburg-Marquardt minimisation, but this is not yet
recommended for general use.
This work was made possible by generous funding from the
Qatar National Research Fund (NPRP grant 08-643-1-112). The
main personnel who have worked to create, test and apply the
code are: Steven Bamford (Nottingham), Boris Haeussler
(Nottingham/Oxford/ESO), Marina Vika (CMU-Qatar) and Alex Rojas
(CMU-Qatar). Others who have directly contributed to the
development and early science verification include Benedetta
Vulcani (CMU-Q/IPMU), Lee Kelvin (St.Andrews/UWA/Innsbruck),
Marco Barden (Innsbruck), Chien Peng (Carnegie Obs./GMTO),
Arianna Cortesi (Nottingham/IAG-USP), Rebecca Kennedy
(Nottingham), Jim Cresswell (CMU-Q), Andrea Borch
(CMU-Q). The core-Sérsic model was implemented by Paolo
Our developments build upon the existing code and efforts
of Chien Peng (GALFIT) and Marco Barden (GALAPAGOS), and we
are indebted to them for allowing us to include our
developments in their software. Much of the advice given on
their respective websites is equally applicable to our
versions, and any publications based on our software should
also cite the appropriate original GALFIT
Some documentation is provided below, but it is still
rather incomplete. For now, we also recommend emailing the
relevant maintainer(s) for further advice on using the
Our software is available below. Please bear in mind
that this is work in progress, and while some features
are complete and well-tested, others are less so.
For important information about recent changes, please
consult the release notes.
Primarily maintained by Steven Bamford.
The latest version is 1.4.4. Executables for various
platforms can be downloaded from the links below.
Versions 1.4.x enable the use of higher-order functions
(bending, fourier modes, rotation) from GALFIT3. For models
that do not make use of these features, 1.4.x should behave
Note that, for comparisons and compatibility purposes,
any previous version can be obtained by substituting the
version number in the above links.
Documented example input files:
The source code is not distributed publicly due to
licensing issues. Please contact us if
you wish to contribute to the code development or need
executables for another platform.
Primarily maintained by Boris Haeussler.
Development and releases of the GALAPAGOS-2 IDL code are
now hosted on
GitHub. A detailed usage guide and set of examples are
Issues and caveats
- GALFITM should be backward compatible with GALFIT3.
On single-band data most of the code executed is
identical, however constraints are handled in a slightly
different way, which means that you will occasionally see
significant differences in the final parameters returned
by GALFITM and GALFIT3. Please let us know if you have a
FEEDME file that works correctly with GALFIT3 but not
GALFITM. Note however, that there are many additional
options in GALFITM, and so even single-band GALFITM FEEDME
files will often not work with GALFIT3.
- Use of bending modes, fourier modes and rotations
(e.g. to model distortions and spiral arms) is now
implemented in version 1.4.x of GALFITM, with full
multi-band support. These features have received a
reasonable amount of internal testing, but users are
recommended to carefully check their results. Please get
in touch with any issues or success stories. Truncations
are partially implemented but probably do not work
correctly - use them at your own risk!
- Almost all our internal testing has used only the
Sérsic, PSF, exponential disc and sky
functions. The way that we have implemented the multi-band
method means that it should work with any of the standard
GALFIT functions. However, if you discover anything odd,
please let us know.
- GALFITM prior to version 1.2.0 was based upon
GALFIT-3.0.2. It therefore did not include some of Chien
Peng's latest additions to GALFIT. These updates in
GALFIT-3.0.5 were merged into GALFITM version
1.2.0. The changes are mostly minor, primarily the
addition of flags providing information about potential
issues with a fit. However, internally-generated sigma
images are now smoothed, which generally results in
small (but occasionally significant) changes to fitting
results. Feedback on this is welcomed.
- Although implemented, the use of MultiNest sampling
has not been tested much, and is very slow, prohibitively
so for models with multiple components and wavelength
freedom. It is definitely not ready for serious use.
- GALFITM is still in active (though sporadic) development, and there
are some rough areas that could do with some work to
make them more suitable for public use. While the
central functionality is unikely to change
substantially, the software will continue to be refined
and polished. New versions, and the changes involved,
will be announced here and via our Facebook group.
We maintain a suite of
for GALFIM. These are primarily for our own internal use in
regression testing new versions. However, users may find
them a useful source of examples, illustrating the range of
functionality in GALFITM. Feel free to open a pull request
with your own tests!
The papers below were produced by the MegaMorph team.
et al., 2010, "Measuring the Physical Properties of
Galaxy Components Using Modern Surveys", ADASS XX conf.
et al., 2013, "MegaMorph - multiwavelength measurement of
galaxy structure: Sérsic profile fits to
galaxies near and far", 2013, MNRAS, 435, 623
et al., 2013, "MegaMorph - multiwavelength measurement of
galaxy structure: complete Sérsic profile
information from modern surveys", MNRAS, 430,
et al., 2014, "Galaxy And Mass Assembly (GAMA):
the wavelength-dependent sizes and profiles of galaxies
revealed by MegaMorph", MNRAS, 441, 1340
et al., 2014, "MegaMorph - multi-wavelength measurement of
galaxy structure: physically meaningful bulge-disk
decomposition of galaxies near and far", MNRAS, 444, 3603
et al., 2015, "MegaMorph: classifying galaxy morphology
using multi-wavelength Sérsic profile fits",
A&A, 577, 97
et al., 2022, "GALAPAGOS-2/GALFITM/GAMA - Multi-wavelength
measurement of galaxy structure: Separating the properties
of spheroid and disk components in modern surveys",
A&A, 664, 92
The following series of papers apply MegaMorph to study
the bulge-disk properties of galaxies in GAMA survey.
et al., 2015, "Galaxy And Mass Assembly (GAMA): the
wavelength dependence of galaxy structure versus redshift
and luminosity", MNRAS, 454, 806
et al., "Galaxy And Mass Assembly (GAMA): understanding
the wavelength dependence of galaxy structure with
bulge-disc decompositions", MNRAS, 460, 3458
et al., 2015, "Galaxy And Mass Assembly (GAMA): Galaxy
colour gradients versus colour, structure, and
luminosity", A&A, 593, A84
Some related papers, which make use of GALFITM and/or
GALAPAGOS-2, are listed below.
2014, "GALFIT-CORSAIR: Implementing the Core-Sérsic Model
Into GALFIT", PASP, 126, 935
et al., 2017, "The effects of the cluster environment on
the galaxy mass-size relation in MACS J1206.2-0847", A&A,
et al., 2017, "Galaxy Zoo: finding offset discs and bars
in SDSS galaxies", MNRAS, 469, 3363
et al., 2018, "Galaxy Zoo: secular evolution of barred
galaxies from structural decomposition of multiband
images", MNRAS, 473, 4731
et al., 2018, "A catalog of polychromatic bulge-disc
decompositions of ∼17.600 galaxies in CANDELS", MNRAS, 478,
et al., 2020, "Multi-wavelength structure analysis of
local cluster galaxies. The WINGS projects", A&A, 633,
et al., 2021, "Recovering the origins of the lenticular
galaxy NGC 3115 using multiband imaging", MNRAS, 504,
et al., 2021, "Extending the evolution of the stellar
mass-size relation at z ≤ 2 to low stellar mass galaxies
from HFF and CANDELS", MNRAS, 506, 928
Collaboration et al., 2023, "Euclid preparation. XXV.
The Euclid Morphology Challenge: Towards model-fitting
photometry for billions of galaxies", A&A, 671, 101
Collaboration et al., 2023, "Euclid preparation. XXVI.
The Euclid Morphology Challenge: Towards structural
parameters for billions of galaxies", A&A, 671, 102
software by Evelyn Johnston makes use of GALFITM to
perform bulge-disc decomposition of MaNGA and MUSE IFU data.
et al., 2017, "SDSS-IV MaNGA: bulge-disc decomposition of
IFU data cubes (BUDDI)", MNRAS, 465, 2317
et al., 2018, "Spectroscopic decomposition of the galaxy
and halo of the cD galaxy NGC 3311", MNRAS, 478, 4255
et al., 2021, "Formation of S0s in extreme environments
II: The star-formation histories of bulges, discs, and
lensess", MNRAS, 500, 4193
et al., 2022, "BUDDI-MaNGA I: A statistical sample of
cleanly decomposed bulge and disc spectra", MNRAS, 514, 6120
et al., 2022, "BUDDI-MaNGA II: the star-formation
histories of bulges and discs of S0s", MNRAS, 514, 6141