Molecular content of polar-ring galaxies

TL;DR

This study investigates the molecular gas content of 21 polar-ring galaxies, detecting CO in five, revealing their gas-rich nature and implications for galaxy formation, dark matter, and galaxy evolution.

Contribution

It provides the first molecular gas measurements for a significant sample of polar-ring galaxies, highlighting their gas richness and deviations from typical galaxy relations.

Findings

Five CO-rich systems detected among 21 PRGs

Average molecular mass of 9.4 x 10^9 solar masses

Gas fraction ranges from 15% to 43% of baryonic mass

Abstract

We have searched for CO lines in a sample of 21 new morphologically determined polar-ring galaxies (of which nine are kinematically confirmed), obtained from a wide search in the Galaxy Zoo project by Moiseev and collaborators. Polar-ring galaxies (PRG) are a unique class of objects, tracing special episodes in the galaxy mass assembly: they can be formed through galaxy interaction and merging, but also through accretion from cosmic filaments. Furthermore, they enable the study of dark matter haloes in three dimensions. The polar ring itself is a sub-system rich in gas, where molecular gas is expected, and new stars are formed. Among the sample of 21 PRG, we have detected five CO-rich systems, that can now be followed up with higher spatial resolution. Their average molecular mass is 9.4 10**9 Mo, and their average gas fraction is 27% of their baryonic mass, with a range from 15 to 43%, implying that they just accreted a large amount of gas. The position of the detected objects in the velocity-magnitude diagram is offset from the Tully-Fisher relation of normal spirals, as was already found for PRGs. This work is part of our multi-wavelength project to determine the detailed morphology and dynamics of polar-ring galaxies, test through numerical models their formation scenario, and deduce their dark matter content and 3D-shape.