pafit 2.0.8

PaFit: Galaxies Kinematic Position Angle Fitting

The PaFit Package

Kinematic Position Angle Fitting for Galaxies

The PaFit package is a Python-based tool to determine the global kinematic position angle of galaxies. This is done by analyzing the observed integral-field stellar or gas kinematics of the galaxies, using the algorithm described in Appendix C of Krajnovic et al. (2006).

Contents

• The PaFit Package

  • Attribution

  • Installation

  • Documentation

• fit_kinematic_pa

  • Purpose

  • Calling Sequence

  • Input Parameters

  • Optional Keywords

  • Output Parameters

• License

• Changelog

Attribution

If you use this software for your research, please cite Krajnovic et al. (2006). The BibTeX entry for the paper is:

@Article{Krajnovic2006,
    title = {Kinemetry: a generalization of photometry to the higher moments
        of the line-of-sight velocity distribution},
    author = {{Krajnovi{\'c}}, D. and {Cappellari}, M. and {de Zeeuw}, P.~T.
        and {Copin}, Y.},
    journal = {MNRAS},
    eprint = {arXiv:astro-ph/0512200}
    year = {2006},
    pages = {787-802},
    volume = {366},
    doi = {10.1111/j.1365-2966.2005.09902.x}
}

Installation

install with:

pip install pafit

Without writing access to the global site-packages directory, use:

pip install --user pafit

To upgrade PaFit to the latest version use:

pip install --upgrade pafit

Documentation

See the pafit/fit_kinematic_pa.py file docstring or PyPi.

---

fit_kinematic_pa

Purpose

Determine the global kinematic position angle of a galaxy from integral-field kinematics of the stars or gas with the method described in Appendix C of Krajnovic et al. (2006)

Calling Sequence

angBest, angErr, vSyst = fit_kinematic_pa(
    x, y, vel, debug=False, nsteps=361, quiet=False, plot=True, dvel=10)

Input Parameters

xbin, ybin:

Vectors with the coordinates of the bins (or pixels) measured from the centre of rotation (typically the galaxy centre).

IMPORTANT: The routine will not give meaningful output unless (x, y) = (0, 0) is an estimate of the centre of rotation.

vel:

Measured velocity at the position (xbin, ybin).

IMPORTANT: An estimate of the systemic velocity has to be already subtracted from this velocity [e.g. vel_corr = vel - np.median(vel)]. The routine will then provide in the output velsyst a correction to be added to the adopted systemic velocity.

dvel:

Scalar with the typical uncertainty in the velocity vel or vector with the uncertainty of each bin (xbin, ybin).

Optional Keywords

nsteps:

Number of steps along which the angle is sampled. Default is 361 steps which gives a 0.5 degr accuracy. Decrease this number to limit computation time during testing.

Output Parameters

anglebest:

Kinematical PA. Note that this is the angle along which |vel| is maximum (note modulus!). If one reverses the sense of rotation in a galaxy anglebest does not change. The sense of rotation can be trivially determined by looking at the map of Vel.

angleerror:

Corresponding error to assign to anglebest.

velsyst:

Best-fitting correction to the adopted systemic velocity for the galaxy.

If the median was subtracted to the input velocity vel before the pa fit, then the corrected systemic velocity will be

---

License

Other/Proprietary License

Copyright (c) 2005-2023 Michele Cappellari

This software is provided as is without any warranty whatsoever. Permission to use, for non-commercial purposes is granted. Permission to modify for personal or internal use is granted, provided this copyright and disclaimer are included in all copies of the software. All other rights are reserved. In particular, redistribution of the code is not allowed.

---

Changelog

V2.0.8: MC, Oxford, 3 April 2023

• Included kwargs keyword passed to plot_velfield.

• Subtract np.median(vel) in the example.

• Formatted documentation as docstring.

• Published documentation on PyPi.

V2.0.7: MC, Oxford, 23 March 2021

• Some documentation updates.

V2.0.6: MC, Oxford 12 May 2018

• Dropped Python 2.7 support.

V2.0.5: MC, Oxford, 17 April 2018

• Changed imports for plotbin as package.

V2.0.4: MC, Oxford, 17 March 2017

• Use Numpy np.percentile instead of deprecated Scipy version.

V2.0.3: MC, Oxford, 7 September 2015

• Changed color of plotted lines.

• Check matching of input sizes.

V2.0.2: MC, Sydney, 2 February 2015

• Fixed possible program stop.

V2.0.1: MC, Oxford, 25 May 2014

• Support both legacy Python 2.7 and Python 3.

V2.0.0: MC, Oxford, 10 April 2014

• Translated from IDL into Python.

V1.3.1: MC, Oxford, 2 December 2013

• Uses CAP_RANGE routine to avoid potential naming conflicts.

• Uses TOLERANCE keyword of TRIANGULATE to try to avoid IDL error “TRIANGULATE: Points are co-linear, no solution.”

V1.3.0: MC, Oxford, 8 October 2013

• The program is two orders of magnitude faster, thanks to a new cap_symmetrize_velfield routine.

V1.2.0: MC, Oxford, 23 March 2010

• Includes error in chi^2 in the determination of angErr. Thanks to Davor Krajnovic for reporting problems.

V1.1.5: MC, Oxford, 14 October 2009

• Overplot best PA on data. Some changes to the documentation.

V1.1.4: MC, Oxford, 31 March 2009

• Clarified that systemic velocity has to be subtracted from VEL.

V1.1.3: MC, Leiden, 25 May 2008

• Determine plotting ranges from velSym instead of vel. Thanks to Anne-Marie Weijmans.

V1.1.2: MC, Oxford, 19 October 2007

• Force error to be larger than 1/2 of the angular step size.

V1.1.1: MC, Oxford, 17 October 2007

• Corrected handling of NSTEPS keyword. Thanks to Roland Jesseit.

V1.1.0: MC, Oxford, 9 October 2007

• Written documentation.

V1.0.0: Michele Cappellari, Leiden, 30 May 2005

• Written and tested