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NGC 5907 with Tidal Stream

This image shows outstanding detail of an extended stellar tidal stream wrapping around NGC 5907, an edge-on, spiral galaxy. The deep image reveals for the first time a large- scale complex of arcing loops—an excellent example of how a low-mass satellite accretion can produce a interweaved, rosette-like structure of debris dispersed in the halo of its host galaxy. The existence of this structure, which has probably survived for several billion years, confirms that halos of spiral galaxies in the Local Universe still contain a significant number of galactic fossils from their hierarchical formation.

Until now, NGC 5907 has been considered a prototypical example of a warped spiral in relative isolation. The presence of an extended tidal stream challenges this picture and suggests that the gravitational perturbations induced by the stream progenitor may be the cause for the warp. This detection of an old, complex tidal stream in a nearby galaxy with rather modest instrumentation points to the viability of surveys to find extragalactic tidal substructures around spiral galaxies in the Local Volume (< 15 Mpc) with the prospect of obtaining a census with enough statistical significance to be compared with cosmological simulations.