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