Stellar Streams in the Solar Neighbourhood from High Resolution N-Body Simulations

A high-resolution N -body simulation suggests that stellar streams in the discs of barred galaxies are common and strongly timedependent. The velocity distribution of stars in the Solar neighbourhood betray many such streams, including a stream of outward moving stars with low angular momentum. This stream is interpreted as a signature of the Galactic bar, in the sense that its stars have just enough energy (Jacobi’s integral) to cross the corotation resonance. 1. The Herculis stream Figure 1 shows the observed velocity distribution in the U -V plane, based on the Hipparcos input (radial velocities) and output (tangential velocities) catalogues. The distribution is characterised by several distinct streams, and in particular a stream with an asymmetric drift of 40− 50 km s and U > 0, which hereafter we will refer to as the “Herculis” stream according to a comoving Eggen group (Skuljan et al. 1999). This stream most probably has a dynamical origin because its stars are mainly older than a few Gyr and present a large range of metallicities (Raboud et al. 1998), and is under-represented in the Hipparcos sample, which is biased towards young stars. The average luminosity of stars in this sample indeed increases with distance and the sample only covers the vertical region of the galactic plane where the fraction of young stars is largest.