This is my accidental contribution to Heather Morrison's Spaghetti Project. The gist of the project is to map the substructure of the Milky Way's stellar halo using K-giants as distance indicators. What I have done here is to take simulations of dwarf galaxies accreted by the Milky Way (simulations were done by Paul Harding) and "observe" the star streams they create. What we see is that while it can be difficult to resolve the streams spatially, they show a clear signature in phase space.
Here are my observations 6 representative disrupted dwarf galaxies; each galaxy is 10^7 solar masses and is observationed after evolving in a static MW potential for 10 Gyr. The galaxies differ only in the initial conditions of their orbits. The number of particles plotted here is normalized to the number of K-giants expected in the dwarf galaxy, making reasonable assumptions about the stellar populations, etc. Each galaxy has two different files here, each with several plots: a Galactocentric Position-Velocity and a LOS Phase Space file.
The galaxy numbers don't actually mean anything, they are just identifiers.
| Galaxy | Galactocentric Position-Velocity | LOS PhaseSpace |
|---|---|---|
| 1023 | GIF | GIF |
| 1070 | GIF | GIF |
| 1263 | GIF | GIF |
| 3225 | GIF | GIF |
| 3238 | GIF | GIF |
| 6866 | GIF | GIF |
From these results we see that streams can be indentified as long, thin features in phase space, due to the large errors associated with spectroscopic parallax distance measurements of the K-giants. Streams are much more difficult to detect when looking towards the galactic center due to the fact that the r^-3.5 halo is very centrally concentrated. Also, streams tend to be easier to detect at large galactocentric distance, both because there are fewer background halo stars, and objects at large radii tend to disrupt more slowly, meaning their stellar streams are denser and thus more easily identified. Finally, from these data alone it is impossible to uniquely determine membership to the dirupted dwarf galaxy; star streams from distupted galaxies occur as overdensities, but background stars from the smooth stellar halo are still present within the overdense regions.
Created by Craig Rudick, 2006.
Last modified 05/10/06.
