2D Bayesian automated tilted-ring fitting of disk galaxies in large HI galaxy surveys: 2DBAT

TL;DR

This paper introduces 2DBAT, a Bayesian algorithm for automated 2D tilted-ring analysis of galaxy velocity fields, improving robustness and automation for large HI survey data, especially useful for upcoming SKA observations.

Contribution

The paper presents a novel Bayesian-based algorithm, 2DBAT, that enhances tilted-ring fitting by reducing local minima issues and enabling fully automated analysis of galaxy kinematics.

Findings

2DBAT performs well on artificial and real HI data.

Optimal for well-resolved, intermediate-inclination galaxies.

Less effective for highly inclined galaxies.

Abstract

We present a novel algorithm based on a Bayesian method for 2D tilted-ring analysis of disk galaxy velocity fields. Compared to the conventional algorithms based on a chi-squared minimisation procedure, this new Bayesian-based algorithm suffers less from local minima of the model parameters even with highly multi-modal posterior distributions. Moreover, the Bayesian analysis, implemented via Markov Chain Monte Carlo (MCMC) sampling, only requires broad ranges of posterior distributions of the parameters, which makes the fitting procedure fully automated. This feature will be essential when performing kinematic analysis on the large number of resolved galaxies expected to be detected in neutral hydrogen (HI) surveys with the Square Kilometre Array (SKA) and its pathfinders. The so-called '2D Bayesian Automated Tilted-ring fitter' (2DBAT) implements Bayesian fits of 2D tilted-ring models in order to derive rotation curves of galaxies. We explore 2DBAT performance on (a) artificial HI data cubes built based on representative rotation curves of intermediate-mass and massive spiral galaxies, and (b) Australia Telescope Compact Array (ATCA) HI data from the Local Volume HI Survey (LVHIS). We find that 2DBAT works best for well-resolved galaxies with intermediate inclinations (20 deg < i < 70 deg), complementing three-dimensional techniques better suited to modelling inclined galaxies.