TY - GEN

T1 - What Is a galaxy? How cold Is cold dark matter?

T2 - Recent progress in near field cosmology

AU - Gilmore, G.

AU - Zucker, D. B.

AU - Wilkinson, M.

AU - Wyse, Rosemary F. G.

AU - Belokurov, V.

AU - Kleyna, Jan

AU - Koch, Andreas

AU - Evans, N. W.

AU - Grebel, E. K.

PY - 2008

Y1 - 2008

N2 - There has been a vast recent improvement in photometric and kinematic data for star clusters, Ultra Compact dwarfs, galactic nuclei, and local dSph galaxies, with Subaru contributing substantially to the photometric studies in particular. These data show that there is a bimodal distribution in half-light radii, with stable star clusters always being smaller than 35pc, while stable galaxies are always larger than 120pc. We extend the previously known observational relationships and interpret them in terms of a more fundamental pair of intrinsic properties of dark matter itself: dark matter forms cored mass distributions, with a core scale length of greater than about 100pc, and always has a maximum central mass density with a narrow range. The dark matter in dSph galaxies appears to be clustered such that there is a mean volume mass density within the stellar distribution which has the very low value of about 0.1M⊙ pc−3. None of the dSphs displays kinematics which require the presence of an inner cusp, while in two dSphs there is evidence that the density profile is shallow (cored) in the inner regions. The maximum central dark matter density derived is model dependent, but is likely to have a mean value (averaged over a volume of radius 10pc) of about 0.1M⊙ pc−3, which is 5GeV/c2cm−3). Galaxies are embedded in dark matter halos with these properties; smaller systems containing dark matter are not observed.

AB - There has been a vast recent improvement in photometric and kinematic data for star clusters, Ultra Compact dwarfs, galactic nuclei, and local dSph galaxies, with Subaru contributing substantially to the photometric studies in particular. These data show that there is a bimodal distribution in half-light radii, with stable star clusters always being smaller than 35pc, while stable galaxies are always larger than 120pc. We extend the previously known observational relationships and interpret them in terms of a more fundamental pair of intrinsic properties of dark matter itself: dark matter forms cored mass distributions, with a core scale length of greater than about 100pc, and always has a maximum central mass density with a narrow range. The dark matter in dSph galaxies appears to be clustered such that there is a mean volume mass density within the stellar distribution which has the very low value of about 0.1M⊙ pc−3. None of the dSphs displays kinematics which require the presence of an inner cusp, while in two dSphs there is evidence that the density profile is shallow (cored) in the inner regions. The maximum central dark matter density derived is model dependent, but is likely to have a mean value (averaged over a volume of radius 10pc) of about 0.1M⊙ pc−3, which is 5GeV/c2cm−3). Galaxies are embedded in dark matter halos with these properties; smaller systems containing dark matter are not observed.

M3 - Conference contribution/Paper

SN - 9781583816684

T3 - ASP Conference Series

SP - 453

EP - 456

BT - Panoramic Views of Galaxy Formation and Evolution

A2 - Kodama, Tadayuki

A2 - Yamada, Toru

A2 - Aoki, Kentaro

ER -