2019MNRAS.482.2284B

We report deep imaging of a 15 x 150 kpc tail in the Hickson Compact Group 98 (HCG 98) observed with a 28-inch telescope at the Wise Observatory and confirmed with additional observations with a similar 28-inch at the Polaris Observatory and with archival and public observations. The tail extends from the general region of the two brightest galaxies of the group to the South-East; it is actually not connected to these galaxies but is linked with an extended low surface brightness envelope or halo around the two main galaxies of the group, approximately opposite to the tail, forming a tadpole-like entity which we assume is at the same distance as the galaxy group. The group is approximately centred on this halo, whose dimensions are 170 kpc (major axis) by 69 kpc (minor axis). We used the co-added Sloan Digital Sky Survey images from the IAC Stripe 82 Legacy Project (with the HCG 98 group shown in Roman & Trujillo); these are 2–3 mag deeper than the regular Sloan Digital Sky Survey images. We measure the brightness and colours of these features, and study the morphology of the galaxies connected with them and of the diffuse features. We propose that our findings can be understood as a stage of a triple dry merger by the two brightest galaxies of the group with a gas-poor dwarf galaxy (M_r ≃ -16.7 mag; the 'victim'), with the tail and head nebulous features originating from its disrupted stars. The fate of the group, once all three objects complete their merging, is probably to form a gE or cD galaxy with M_r ≃ -22.1 mag, stressing that this merging process into a giant galaxy need not take place at the centre of a rich cluster of galaxies.