Malin 1: interacting galaxy pair?

TL;DR

This study investigates the stellar kinematics of Malin 1's inner region, revealing a possible interacting companion galaxy Malin 1B and suggesting that such interactions may explain its unique large-scale structure.

Contribution

First spectroscopic evidence of a small companion galaxy Malin 1B interacting with Malin 1, providing insights into its morphology and potential formation scenarios.

Findings

Malin 1B is located 14 kpc from Malin 1's nucleus with a relative velocity of 65 km/s.

Interaction with Malin 1B may explain Malin 1's spiral and bar structures.

A nearby galaxy might have contributed to Malin 1's extended low-surface brightness envelope.

Abstract

Malin 1 is a unique, extraordinarily large low surface brightness galaxy. The structure and the origins of the galaxy are poorly understood. The reason for such a situation is an 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 Malin 1. We present spectroscopic arguments in favour of a small galaxy - Malin 1B - being a companion probably interacting with the main galaxy - Malin 1. This object is clearly seen in many published images of Malin 1 but is not mentioned in any astronomical databases. Malin 1B is located at the projected distance of 14 kpc from the Malin 1's nucleus and has small - 65$\pm$16 km/s - relative velocity, which we determined for the first time. We suggest that ongoing interaction with Malin 1B can explain main morphological features of the Malin 1's central region - two-armed spiral structure, a bar, and an external one-armed spiral pattern. We also investigated the large scale environment of Malin 1 and postulate that the galaxy SDSS J123708.91+142253.2 might be responsible for the formation of extended low-surface brightness envelope by means of head-on collision with Malin 1 (in the framework of collision scenario proposed by Mapelli et al. 2008). To test the collisional origins of Malin 1 global structure, more observational data and new numerical models are needed.