galfit-uv

Parametric UV visibility fitting for ALMA data. galfit-uv extracts visibilities from CASA measurement sets, fits surface-brightness models (point source, Gaussian, Sersic) via MCMC using numerical Hankel transforms, and produces UV plots, clean images, and diagnostic figures. The package supports multi-component models with configurable geometry tying and fixed-parameter constraints.

Features

• Visibility export from CASA measurement sets with variable-shape column handling and time binning
• Parametric profiles: point source, Gaussian, and generalized Sersic
• MCMC fitting with emcee, Jeffreys and sin(incl) priors, and automatic convergence checks
• Multi-component models (up to 2 profiles) with configurable geometry tying
• Clean imaging via CASA tclean — data, model, and residual side by side
• Diagnostic plots: UV visibility comparison, corner plots, and walker chains

Installation

Requires a CASA conda environment (provides casatools and casatasks):

conda activate alma
pip install -e /path/to/Galfit-uv

Dependencies:

Package	Source
numpy, scipy	pip / conda
emcee, dill	pip
matplotlib, corner	pip
astropy	pip / conda
casatools, casatasks	CASA conda environment (not pip-installable)

Note: Always import galfit_uv (not submodules directly) so that __init__.py can set threading environment variables before numpy loads.

Quick Start

A complete four-step workflow: export, model, fit, and plot.

import galfit_uv

# 1. Export visibilities from a measurement set
dvis, wle = galfit_uv.export_vis('target.ms', verbose=True)

# 2. Build a model (e.g., single Sersic profile)
model_fn, param_info = galfit_uv.make_model_fn(['sersic'])

# 3. Fit with MCMC
result = galfit_uv.fit_mcmc(
    dvis, model_fn, param_info,
    max_steps=5000, burnin=2500, nwalk_factor=5,
    outpath='./fit_output', seed=42,
)

# 4. Plot data vs model
uv = (dvis.u, dvis.v)
mvis = model_fn(result.bestfit, uv)
galfit_uv.plot_uv(dvis, mvis, outpath='./figs', fname='uvplot.png')

Demo data: The measurement set used in the examples (GQC J0054-4955) can be downloaded from: https://drive.google.com/file/d/1TPZQvP-7wc5Kk169Gh6IgiYAUoaug2bb/view?usp=sharing

Available Profiles

Profile	Intrinsic parameters	Description
point	flux (mJy)	Unresolved source
gaussian	flux (mJy), sigma (arcsec)	Gaussian surface brightness
sersic	flux (mJy), Re (arcsec), n	Generalized Sersic profile

All profiles share geometry parameters: incl, PA, dx, dy.

Multi-component models (e.g., ['sersic', 'point']) support configurable geometry tying via tie_center, tie_incl, tie_pa flags, and fixed parameters via the fixed dict.

Units Convention

Quantity	Internal units	Display units
Visibility amplitudes	Jy (complex)	mJy
Flux parameters	mJy	mJy
Size parameters (sigma, Re)	arcsec	arcsec
UV coordinates (u, v)	wavelengths (lambda)	kilo-lambda
Wavelength (wle)	meters	mm

Next Steps

• Examples — Walk through fitting real ALMA data (GQC J0054-4955) with two different models
• API Reference — Full function signatures, parameters, and return values

Citation

If you use galfit_uv in your research, please cite:

Long, F. et al. 2021, ApJ, 915, 131 — ADS

Acknowledgements

Development of this code was assisted by Claude Code and GLM-5.