  General structural properties and low surface brightness tidal features hold
important clues to the formation of galaxies. In this paper, we study a sample
of polar-ring galaxies (PRGs) based on optical imaging from the Sloan Digital
Sky Survey (SDSS) Stripe82 and other deep surveys. We investigate the deepest
images of candidates for PRGs to date. We carry out photometric decomposition
on the host galaxies and associated polar structures that allows us to derive
the structural properties of both components. We are able to detect very faint
tidal structures around most PRGs in our sample. For several galaxies, we can
directly observe the formation of the polar ring due to merging, which is
manifested in debris of the victim galaxy and an arc-like polar structure made
up of its material. In a few cases, we can discern signs of tidal accretion.
The results obtained indicate that the gravitational interaction and merging of
galaxies are the most plausible mechanisms for the formation of polar-ring
galaxies.

Astrophysics of Galaxies