Inclinations and Position Angles for Disc Galaxies in the SGA sample

TL;DR

This paper introduces a fast, data-driven Fourier-Laguerre based method to accurately determine the inclination and position angles of disc galaxies, demonstrating high reproducibility and minimal failures across a large galaxy sample.

Contribution

The authors develop and validate a novel Fourier-Laguerre based technique for measuring galaxy inclinations and PAs, applicable to large survey data with high accuracy and efficiency.

Findings

Reproduces published inclination and PA within 10° and 5° median error.

Demonstrates zero catastrophic failures in measurements.

Provides measurements for over 130,000 disc galaxies in multiple bands.

Abstract

We present a data-driven method for determining the inclination and position angle (PA) of disc galaxies using a Fourier-Laguerre basis decomposition of imaging data. We define a dimensionless metric, $\eta$, that characterises the ratio of the quadrupole and monopole coefficients in the Fourier-Laguerre basis function expansion. This metric serves as a robust measure which is related to the inclination of a galaxy. We find an empirical relationship between $\eta$ and inclination which is agnostic to the galaxy morphology. The PA is derived directly from the phase of the quadrupolar Fourier-Laguerre functions. Across a benchmark sample of galaxies, the method reproduces published inclination and PA values to within a median of 10$^\circ$ and 5$^\circ$, respectively, while also demonstrating essentially zero catastrophic failures. Applying this pipeline to galaxies from the Siena Galaxy Atlas (SGA), we report measurements of $\eta$, scale length and PA for three different bands of 133,942 disc galaxies. Our computationally inexpensive technique automates parametrisation analysis and returns reproducible results for large surveys. We release a Python package ready for application to next generation surveys.