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The Ghost of a Dwarf Galaxy: Fossils of the Hierarchical Formation of the Nearby Spiral Galaxy NGC 5907

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David Martínez-Delgado1,2,3, Jorge Peñarrubia4, R. Jay Gabany5, Ignacio Trujillo1,3, Steven R. Majewski6 and M. Pohlen7

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We present an extragalactic perspective of an extended stellar tidal stream wrapping around the edge-on spiral galaxy NGC 5907. Our deep images reveal for the first time a large-scale complex of arcing loops that is an excellent example of how low-mass satellite accretion can produce an interwoven, rosette-like structure of debris dispersed in the halo of its host galaxy. The existence of this structure, which has probably formed and survived for several gigayears, confirms that halos of spiral galaxies in the local universe may still contain a significant number of galactic fossils from their hierarchical formation. To examine the validity of the external accretion scenario, we present N-body simulations of the tidal disruption of a dwarf galaxy-like system in a disk galaxy plus dark halo potential that demonstrate that most of the tidal features observed in NGC 5907 can be explained by a single accretion event. Unfortunately, with no kinematic data and only the projected geometry of the stream as a constraint, the parameters of our model are considerably degenerate and, for now, must be considered illustrative only. Interestingly, NGC 5907 has long 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 must be considered as a possible cause for the warp. The 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.

Subject headings

dark matter; galaxies: dwarf; galaxies: evolution; galaxies: halos; galaxies: individual (NGC 5907); galaxies: interactions


Dates

Issue 1 (2008 December 10)

Received 2008 May 7, accepted for publication 2008 August 12



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