NGC 5523: An Isolated Product of Soft Galaxy Mergers?

TL;DR

This study presents multi-band imaging evidence suggesting that the isolated spiral galaxy NGC 5523 has undergone significant, non-disruptive mergers, challenging the idea that isolation implies a lack of interaction history.

Contribution

It provides observational evidence linking galaxy isolation with past merger events, highlighting features indicative of such interactions in NGC 5523.

Findings

Presence of a nucleated bulge embedded in the disk

Offset of the bulge from the galaxy center

Detection of a tidal stream suggesting satellite interaction

Abstract

Multi-band images of the very isolated spiral galaxy NGC 5523 show a number of unusual features consistent with NGC 5523 having experienced a significant merger: (1) Near-infrared (NIR) images from the Spitzer Space Telescope (SST) and the WIYN 3.5-m telescope reveal a nucleated bulge-like structure embedded in a spiral disk. (2) The bulge is offset by ~1.8 kpc from a brightness minimum at the center of the optically bright inner disk. (3) A tidal stream, possibly associated with an ongoing satellite interaction, extends from the nucleated bulge along the disk. We interpret these properties as the results of one or more non-disruptive mergers between NGC 5523 and companion galaxies or satellites, raising the possibility that some galaxies become isolated because they have merged with former companions.