Malin 1: interacting galaxy pair?

Malin1 is a unique, extraordinarily large low-surface brightness galaxy. The structure and the origins of the galaxy are poorly understood. The reason for this is the absence of detailed observational data, especially of high-resolution kinematics. In this Letter, we study the stellar kinematics of the inner part (r≤ 15 kpc) of Malin1. We present spectroscopic arguments in favour of a small galaxy – Malin1B – being a companion probably interacting with the main galaxy – Malin1. This object is clearly seen in many published images of Malin1 but is not mentioned in any astronomical data bases. Malin1B is located at a projected distance of 14kpc from Malin1's nucleus and has small – 65 ± 16km s−1– relative velocity, which we determined for the first time. We suggest that the ongoing interaction with Malin1B can explain the main morphological features of Malin1's central region – two-armed spiral structure, a bar and an external one-armed spiral pattern. We also investigated the large-scale environment of Malin1 and postulated that the galaxy SDSSJ123708.91 + 142253.2 might be responsible for the formation of an extended low-surface brightness envelope by means of head-on collision with Malin1 (in the framework of the collision scenario proposed by Mapelli et al.). To test the collisional origins of Malin1's global structure, more observational data and new numerical models are needed.