Molecular content of polar-ring galaxies ^⋆,⋆⋆

¹ Observatoire de Paris, LERMA, CNRS UMR8112, 61 Av. de l’Observatoire 75014 Paris France
e-mail: francoise.combes@obspm.fr
² Special Astrophysical Observatory, Russian Academy of Sciences, 369167 Nizhnii Arkhyz, Karachaevo-Cherkesskaya Republic, Russia
³ St. Petersburg State University, Universitetskii pr. 28, 198504 St Petersburg, Stary Peterhof, Russia

Received: 28 February 2013
Accepted: 19 April 2013

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 (PRGs) 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 PRGs, we have detected five CO-rich systems, that can now be followed up with higher spatial resolution. Their average molecular mass is 9.4 × 10⁹M_⊙, and their average gas fraction is 27% of their baryonic mass, with a range from 15 to 43%, implying that they have 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 PRGs, test through numerical models their formation scenario, and deduce their dark matter content and 3D-shape.