Image copyright ©2006-2010 R Jay GaBany.

The Discovery of a Giant Stellar Tidal Stream Around NGC 4013

David Martínez-Delgado ( IACMPIA ),  Michael Pohlen ( Cardiff ),  R. Jay GaBany ( Blackbird Observatory ), 
Steven R. Majewski ( Univ. Virginia ),  Jorge Peñarrubia ( Univ.Victoria ),  Chris Palma ( Penn State )

We report the discovery of a giant, low surface-brightness loop-like stellar structure around the edge-on spiral galaxy NGC4013.The detection of this loop-like structure is independently confirmed in three separate datasets from three different telescopes.The significantly redder colour of the stream material compared to the outer parts of the disk of NGC4013 suggests that this loop did not originate from the disk itself, but rather is the tidal stream of a dwarf galaxy being destroyed in NGC4013's gravitational potential. Although its true three-dimensional geometry is unknown, the projected tidal loop displays a very good overall match with the external edge-on perspective of the Monoceros tidal stream in the Milky Way predicted by recent N-body simulations (Peñarrubia et al. 2005).

Our results demonstrate that NGC4013, previously considered a prototypical isolated disk galaxy, is in fact undergoing a tidal encounter with a low-mass satellite. In this sense NGC4013, with one of the most prominent Hiwarped disks known but showing no previously obvious indication of tidal activity, could be a Rosetta Stone for understanding disks that appear almost pristine in the optical but warped in Hi maps and may provide key insights into the formation of warps in general.

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