A ~ 12 kpc H i extension and other H i asymmetries in the isolated galaxy CIG 340 (IC 2487)

Context. H i kinematic asymmetries are common in late-type galaxies irrespective of environment, although the amplitudes are strikingly low in isolated galaxies. As part of our studies of the H i morphology and kinematics in isolated late-type galaxies we have chosen several very isolated galaxies from the AMIGA sample for H i mapping. We present here the results of H i mapping of CIG 340 (IC 2487) which was selected because its integrated H i spectrum has a very symmetric profile (Aflux = 1.03 ± 0.02). Aims. Optical images of the galaxy hinted at a warped disk in contrast to the symmetric integrated H i spectrum profile. Our aim is to determine the extent to which the optical asymmetry is reflected in the resolved H i morphology and kinematics. Methods. Resolved 21-cm H i line mapping has been carried out using the Giant Metrewave Radio Telescope (GMRT). The H! i morphology and kinematics from this mapping together with other multi-wavelength data have been used to study the relationship between the H i and stellar components of CIG 340. Results. GMRT observations reveal significant H i morphological asymmetries in CIG 340 despite it's overall symmetric optical form and highly symmetric H i spectrum. The most notable H i features are: 1) a warp in the H i disk (with an optical counterpart), 2) the H i north/south flux ratio = 1.32 is much larger than expected from the integrated H i spectrum profile, and 3) a ~ 45′′ (12 kpc) H i extension containing ~6% of the detected H i mass on the northern side of the disk. Conclusions. Overall, we conclude that in isolated galaxies a highly symmetric H i spectrum can mask significant H i morphological asymmetries which can be revealed by H i interferometric mapping. The northern H i extension appears to be the result of a recent perturbation (108 yr), possibly by a satellite which is now disrupted or projected within the disk. But, we cannot rule out that the H i extension and the other observed asymmetries are the result of a long lived dark matter halo asymmetry. This study provides an important step in our ongoing programme to determine the predominant source of H i asymmetries in isolated galaxies. For CIG 340 the isolation from major companions, symmetric H i spectrum, optical morphology and interaction timescales have allowed us to narrow the possible causes the H i asymmetries and identify tests to further constrain the source of the asymmetries. © 2014 ESO.