Insights into the Physical Nature of Polar Ring Galaxies from H I Observations

TL;DR

This study investigates polar ring galaxies using H I observations, revealing their gas properties, dynamics, and deviations from typical galaxy relations, which sheds light on their formation and evolution.

Contribution

It provides a comprehensive H I dataset for PRGs, analyzes their gas dynamics, and highlights the importance of spatially resolved observations for understanding their origins.

Findings

22 H I detections out of 40 PRGs

PRGs have higher gas fractions than early-type galaxies

PRGs' Tully-Fisher relation scatter depends on gas distribution

Abstract

Polar ring galaxies (PRGs) host an outer ring of gas and stars oriented nearly perpendicular to the main stellar body. They represent extreme examples of misaligned systems and provide valuable insight into galaxy interactions, gas accretion, and peculiar gas dynamics. We compile a complete sample of kinematically confirmed PRGs and collect their H I measurements. Combining literature data with new observations from FAST, we detect H I emission in 22 sources, identify one potential H I absorption feature, and find four non-detections among 40 confirmed PRGs. Compared to galaxies in the ALFALFA and xGASS surveys, PRGs predominantly occupy the green valley or quenched regimes but exhibit higher gas fractions than typical early-type galaxies, suggesting gas accretion. The H I profile asymmetry and shape for PRGs are not consistent with that of the ALFALFA sample with p<0.05. We examine their Tully-Fisher relation (TFR) and baryonic TFR (bTFR), linking the systems' rotation velocities to their masses. The extreme outliers in TFRs for the control sample tend to display single-peaked H I profiles. PRGs do not follow a tight TFR or bTFR if the H I resides primarily in the host galaxy. But the scatter decreases significantly if we assume the gas is mainly distributed in the polar ring. Spatially resolved H I observations are essential to disentangle the gas distribution and kinematics in PRGs, which are key to understanding their formation mechanisms.