H I in HO: Hoag's Object revisited

We present new H I observations of Hoag's Object (HO) obtained with the Westerbork Synthesis Radio Telescope. The data show that the luminous optical ring around the elliptical body has a bright H I counterpart that shares the kinematical properties of the optical ring. The entire H I structure is twice as large as the optical ring and shows a mild warp in its outer regions relative to the inner ring. We detect two additional H I sources close in redshift to that of HO, and report on a newly identified SDSS optical companion galaxy. The H I sources are ∼0.3 and ∼1 Mpc away in projected distance, and the companion galaxy is also ∼1 Mpc away. Our main conclusion is that the H I detected in HO shows no indication that this galaxy has experienced a recent (less than ∼1 Gyr ago) accretion event. At least one of the two additional H I detected objects does not have an optical counterpart. One possibility is that this object is an H I filament left over from an interaction shaping HO, in which case this interaction must also have occurred at least 1-2 Gyr ago.