Astronomy and Astrophysics – Astrophysics
Scientific paper
1999-01-07
Astronomy and Astrophysics
Astrophysics
13 pages including 8 ps figures, to appear in The Galactic Halo: Bright Stars and Dark Matter, proceedings of the Third Stroml
Scientific paper
Future astrometric satellites, such as SIM (NASA's Space Interferometric Mission) and GAIA (ESA's Global Astrometric Interferometer for Astrophysics), hold the promise of mapping out the detailed phase space structure of the Galactic halo by providing unprecedented annual proper motion and parallax of $1-10\mu$as astrometric accuracy. Here we show that proper motions of hundred or so giant branch stars in a tidal debris torn from a small satellite (a $10^{5-7}L_\odot$ Galactic dwarf galaxy or globular cluster) in the halo is sensitive to the current Galactic potential and its past evolution. We follow the evolution of a cold (velocity dispersion of 10 km/s) stream on a nearby (between 8-50 kpc) polar orbit in a variety of histories of the potential of the Galaxy, and observe the bright ($V<18$mag) members of the debris tail with GAIA accuracy. We simulate effects due to the growing or flipping of the Galactic disk over the past 4 Gyrs or the perturbation from a massive accreted lump such as the progenitor of the Magellanic Clouds. We study various factors influencing our ability to identify streams, including contamination from field stars, accuracy of radial velocity and distance data and evolution and non-axial symmetry of the potential. Our simulations suggest that nearby, cold streams could be detected with GAIA if these cousins of the Sagittarius stream exist. Results of Johnston, Zhao, Spergel & Hernquist (1999) and Helmi, Zhao & de Zeeuw (1999) for static Galactic potentials are likely to be largely generalizable to moderately time-evolving potentials. SIM and GAIA measurements of debris stars might be used to probe both Galactic structure and Galactic history.
Hernquist Lars
Johnston Kathryn
Spergel David
Zhao HongSheng
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