Dragonfly imaging of the galaxy NGC5907: a revised view of the iconic
  stellar stream
  In 2008 it was reported that the stellar stream of the edge-on spiral NGC5907
loops twice around the galaxy, enveloping it in a giant corkscrew-like
structure. Here we present imaging of this iconic object with the Dragonfly
Telephoto Array, reaching a $1\sigma$ surface brightness level of $\mu_g\approx
30.5$ mag/arcsec$^2$ on spatial scales of 1' (the approximate width of the
stream). We find a qualitatively different morphology from that reported in the
2008 study. The Dragonfly data do not show two loops but a single curved stream
with a total length of 45' (220 kpc). The surface brightness of the stream
ranges from $\mu_g \approx 27.6$ mag/arcsec$^2$ to $\mu_g\approx 28.8$
mag/arcsec$^2$, and it extends significantly beyond the region where tidal
features had previously been detected. We find a density enhancement near the
luminosity-weighted midpoint of the stream which we identify as the likely
remnant of a nearly-disrupted progenitor galaxy. A restricted N-body simulation
provides a qualitative match to the detected features. In terms of its spatial
extent and stellar mass the stream is similar to Sagittarius, and our results
demonstrate the efficacy of low surface brightness-optimized telescopes for
obtaining maps of such large streams outside the Local Group. The census of
these rare, relatively high mass events complements the census of common, low
mass ones that is provided by studies of streams in the Milky Way halo.
