Lenticular galaxies at the outskirts of the Leo II group: NGC 3599 and NGC 3626

TL;DR

This study investigates two lenticular galaxies in the Leo II group, revealing their recent transformation from spirals due to minor mergers, characterized by complex kinematics, star-forming rings, and Seyfert activity, occurring 1-2 billion years ago.

Contribution

It provides detailed observational evidence of the transformation mechanisms of S0 galaxies in a group environment, emphasizing minor mergers over hot intragroup medium effects.

Findings

Evidence of minor mergers in NGC 3599 and NGC 3626

Detection of decoupled gas kinematics and star-forming rings

Signs of Seyfert activity in NGC 3599

Abstract

We have studied unbarred S0 galaxies, NGC 3599 and NGC 3626, the members of the X-ray bright group Leo II, by means of 3D spectroscopy, long-slit spectroscopy, and imaging, with the aim to identify epoch and mechanismsof their transformation from spirals. Both galaxies have appeared to bear a complex of features resulting obviously from minor merging: decoupled gas kinematics, nuclear starforming rings, and multi-tiered oval large-scale stellar disks. The weak-emission line nucleus of NGC 3599 bears all signs of the Seyfert activity, according to the line-ratio diagnostics of the gas excitation mechanism. After all, we conclude that the transformation of these lenticular galaxies has had place about 1-2 Gyr ago, through the gravitational mechanisms not related to hot intragroup medium of Leo II.