Tidal Stream Pilot Survey Overview
ithin the hierarchical framework for galaxy formation, minor merging and tidal interactions are expected to shape large galaxies even up to the present day. As part of a pilot survey, we have carried out ultra deep, wide field imaging of several isolated spiral galaxies in the Local Volume with data produce through small (0.1 to 0.5 meters in diameter), robotic telescopes that provide exquisite surface brightness sensitivity.
According to the standard model, galaxies grow through the disruption and absorbtion of small satellite galaxies. This process occurs over billions of years and leaves a trail of stars marking the satellite's orbit.
- Illustration credit: Jon Lomberg
Our observations have led to the discovery of six previously undetected, gigantic, stellar structures in the halos of several galaxies that are likely associated with debris from satellites that were tidally disrupted far in the distant past. In addition, we also confirmed several enormous stellar structures previously reported in the literature, but never before interpreted as being tidal streams.
Our collection of galaxies presents an assortment of tidal phenomena exhibiting strikingly diverse morphological characteristics. In addition to identifying great circular features that resemble the Sagittarius stream surrounding the Milky Way, our observations have uncovered enormous structures that extend tens of kiloparsecs into the halos of their host's central spiral. We have also found remote shells, giant clouds of debris within galactic halos, jet-like features emerging from galactic disks and large-scale, diffuse structures that are almost certainly related to the remnants of ancient, already thoroughly disrupted satellites. Together with these remains of possibly long defunct companions, our survey also captured surviving satellites caught in the act of tidal disruption. Some of these display long tails extending away from the progenitor satellite very similar to the predictions forecasted by cosmological simulations.
Our comparison with available stellar halo simulations suggests that the extraordinary variety of morphological specimens detected in our survey could represent one of the first comprehensive pieces of evidence to support that the hierarchical formation scenarios predicted by theoretical models apply generally to galaxies similar to the Milky Way in the Local Volume.
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