Dragonfly Imaging of the Galaxy NGC 5907: A Different View of the Iconic Stellar Stream

Abstract

In 2008 it was reported that the stellar stream of the edge-on spiral NGC 5907 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 1σ surface brightness level of µ g = 30.3 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 µ g ≈ 27.6 mag arcsec −2 to µ g ≈ 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.

Hunting ghosts: the iconic stellar stream(s) around NGC 5907 under scrutiny

“…In Figure 2 we compare the relevant part of our image with the Dragonfly g-band image taken by van Dokkum et al (2019). The shape of the stream detected by us and by van Dokkum et al (2019) are identical, which is also apparent when blinking the two images. So where should the double loop reside?…”

“…The recent paper by van Dokkum et al (2019) has stirred a controversy which has been hotly debated at conferences and on social media. To shed light on the discussion, we have independently taken deep data using a 1.4 meter telescope to assess whether there is a double loop structure as found by Martínez-Delgado et al (2008) or rather a simple knee-shaped stream as found by van Dokkum et al (2019). Our imaging is consistent with the latter, with no signs of a double loop.…”

Census and classification of low-surface-brightness structures in nearby early-type galaxies from the MATLAS survey

“…The pitfalls of deep imaging are illustrated by the recent controversy about the tidal streams of the Splinter Galaxy, NGC 5907. Several amateur observers equipped by small telescopes have observed the streams warping the galaxy multiple times -the refereed example is Martínez-Delgado et al (2008) -while the professional astronomers with bigger telescopes were able to detect only a part of this structure (Laine et al 2016;van Dokkum et al 2019;Müller et al 2019c;Alabi et al 2020). The case remains unresolved.…”

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

“…NGC 4565 is the first galaxy in the DEGS sample to be observed, and was observed for significantly longer than typical DEGS targets. The first typical DEGS galaxy to be reduced, NGC 5907, is presented in van Dokkum et al (2019). We observed NGC 4565 over 64 nights from Spring 2015 to Summer 2017.…”