* Astronomy

Blobrana · L

RE: Aquarius Stream

Blobrana · L

Galaxy found hidden in Milky Way

The remains of a dwarf galaxy buried within our own have been discovered by a New Zealand scientist.
Astronomer Mary Williams, who is working with an international team in Germany on a million-star survey, discovered the ''Aquarius Stream'' through careful digging.
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Blobrana · L

A small snack for the Milky Way

An international team of astronomers led by Mary Williams from the Astrophysical Institute Potsdam (AIP) has discovered a new stream of stars in our Milky Way: the "Aquarius Stream," named after the constellation of Aquarius. The stream of stars is a remnant of a smaller galaxy in our cosmic neighbourhood, which has been pulled apart by the gravitational pull of the Milky Way about 700 million years ago. The discovery is a result of the measurement of the velocities of 250,000 stars with the RAVE Survey based at the Australian Astronomical Observatory's UK Schmidt Telescope at Siding Spring Observatory, NSW, Australia.
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Title: The Dawning of the Stream of Aquarius in RAVE
Authors: Mary E. K. Williams, Matthias Steinmetz, Sanjib Sharma, Joss Bland-Hawthorn, Roelof S. de Jong, George M. Seabroke, Amina Helmi, Kenneth C. Freeman, James Binney, Ivan Minchev, Olivier Bienaymé, Rachel Campbell, Jon P. Fulbright, Brad K. Gibson, Gerard F. Gilmore, Eva K. Grebel, Ulisse Munari, Julio F. Navarro, Quentin A. Parker, Warren Reid, Arnaud Siebert, Alessandro Siviero, Fred G. Watson, Rosemary F. G. Wyse, Tomaz Zwitter

We identify a new, nearby (0.5 < d < 10 kpc) stream in data from the RAdial Velocity Experiment (RAVE). As the majority of stars in the stream lie in the constellation of Aquarius we name it the Aquarius Stream. We identify 15 members of the stream lying between 30 < l < 75 and -70< b <-50, with heliocentric line-of-sight velocities V_los~-200 km/s. The members are outliers in the radial velocity distribution, and the overdensity is statistically significant when compared to mock samples created with both the Besan\c{c}on Galaxy model and newly-developed code Galaxia. The metallicity distribution function and isochrone fit in the log g - T_eff plane suggest the stream consists of a 10 Gyr old population with [m/H]~-1.0. We explore relations to other streams and substructures, finding the stream cannot be identified with known structures: it is a new, nearby substructure in the Galaxy's halo. Using a simple dynamical model of a dissolving satellite galaxy we account for the localisation of the stream. We find that the stream is dynamically young and therefore likely the debris of a recently disrupted dwarf galaxy or globular cluster. The Aquarius stream is thus a specimen of ongoing hierarchical Galaxy formation, rare for being right in the solar suburb.

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