The Dragonfly Edge-on Galaxies Survey: Shaping the outer disc of NGC 4565 via accretion

TL;DR

This study uses deep imaging to analyze the outer disc structure of NGC 4565, revealing features consistent with accretion-driven growth and tidal interactions, marking a significant step in understanding galaxy outskirts.

Contribution

First detailed deep imaging of NGC 4565's outer disc showing evidence of accretion and tidal features, supporting models of galaxy growth via external material accretion.

Findings

Confirmed asymmetric disc truncation in NGC 4565.

Identified a fan-like feature possibly caused by tidal interactions.

Provided evidence supporting accretion-driven outer disc growth.

Abstract

We present extremely deep imaging of the well-known edge-on galaxy NGC 4565 (the "Needle Galaxy"), observed as part of the Dragonfly Edge-on Galaxies Survey. Our imaging traces starlight over scales of ~100 kpc to surface brightnesses of ~32 mag/arcsec^2 in azimuthally averaged radial profiles. In narrow slice profiles along the major axis (with bin sizes ranging from 1.7 x 0.5 kpc to 1.7 x 7.8 kpc), we achieve a depth of ~29-30 mag/arcsec^2. We confirm the previously observed asymmetric disc truncation. In addition, the sharp northwest truncation turns over to a shallower component that coincides with a fan-like feature seen to wrap around the northwest disc limb. We propose that the fan may be a tidal ribbon, and qualitatively replicate the fan with simple simulations. Alternative explanations of the fan and the disc's asymmetry are considered as well. We conclude that we are most likely seeing evidence for accretion-based outer disk growth in NGC 4565.