Breaking tidal stream degeneracies with LAMOST. Jorge Peñarrubia (IoA). Cambridge 2nd December 08. Local Group Cosmology. Cosmological Paradigm predicts that galaxies form through mergers of smaller galaxies. This process continues nowadays in the Milky Way…. Local Group Cosmology.
Breaking tidal stream degeneracies with LAMOST
Jorge Peñarrubia (IoA)
Cambridge 2nd December 08
Cosmological Paradigm predicts that galaxies form through mergers of smaller galaxies
This process continues
nowadays in the Milky Way…
The Local Group is the only system where the kinematics of individual stars can be measured with high precision
why is this important?
We want to decompose the hierarchical formation
of our galaxy = set of individual mergers
However, the remnants of accreted satellites
Photometric surveys can only reveal
the most recent accretions
for each accretion event
Peñarrubia et al. (2005)
cosmological merger tree
Proper motions can only be measured in a small volume (GAIA<20 kpc)
In contrast, radial velocities can be measured < 1 Mpc (DEIMOS @ Keck)
Mapping the sky via Radial velocity surveys:
Position + radial velocity = 4D info of stellar streams
to infer the orbit+mass of progenitor
we need numerical modelling
Owing to the large parameter spacemodel degeneracies
(ifprogenitor is unknown)
spectroscopic surveys will break fundamental model degeneracies
Previous photometric surveys have revealed a large number of stream-like structures at D< 50 kpc
Potential targets for LAMOST are:
All located in the Northern Galactic Hemisphere !!
(the South remains terra incognita)
What could we learn if we had LAMOST data now??
Belokurov et al. 2006
from 2-MASS (M-giants) :
Johnston et al. 2005
using the same data
inconsistent results !!
Law et al. 2005
Again, M-Giant over-densities
Do all over-densities belong to the Mon stream?
Penarrubia et al. 2005
Degenerated model : Prograde vs Retrograde orbits
Radial velocities between
l > 220o
l < 110o
will break model degeneracy
In the next few years, the number of streams detected via photometric
surveys (SDSS I,II,III; Pan-STARRS) will dramatically increase.
Kinematics will be crucial for their modelling….
According to CDM, there are ~104 subhaloes in the MW with M>107 Msol
Cold tidal streams (e.g from GCs with ~ 1 km/s) may be heated by encounters with DM subhaloes
kinematical surveys of GC streams could potentially constrain the number density of DM clumps
Grillmair & Dionatos 2006