COSMOLOGICAL SIMULATIONS OF MASSIVE COMPACT HIGH-z GALAXIES

In order to investigate the structure and dynamics of the recently discovered massive (M-* greater than or similar to 10(11) M-circle dot) compact z similar to 2 galaxies, cosmological hydrodynamical/N-body simulations of a similar to 50,000 Mpc(3) comoving (Lagrangian), proto-cluster region have been undertaken. At z = 2, the highest resolution simulation contains similar to 5800 resolved galaxies, of which 509, 27, and 5 have M-* > 10(10) M-circle dot, M-* > 10(11) M-circle dot, and M-* > 4 x 10(11) M-circle dot, respectively. Total stellar masses, effective radii, and characteristic stellar densities have been determined for all galaxies. At z = 2, for the definitely well-resolved mass range of M-* greater than or similar to 10(11) M-circle dot, we fit the relation R-eff = R-eff,R-12 M-*,12(1/3) to the data, where M-*,M-12 is the total stellar mass in units of 10(12) M-circle dot. This yields R-eff,R-12 = (1.20 +/- 0.04) kpc, in line with observational findings for compact z similar to 2 galaxies, though somewhat more compact than the observed average. The only line-of-sight velocity dispersion measured for a z similar to 2 compact galaxy is very large, sigma(*,p) = 510(-95)(+165) km s(-1). This value can be matched at about the 1 sigma level, although a somewhat larger mass than the estimated M-* similar or equal to 2 x 10(11) M-circle dot is indicated. For the above mass range, the galaxies have an average axial ratio < b/a > = 0.64 +/- 0.02 with a dispersion of 0.1, and an average rotation to one-dimensional velocity-dispersion ratio = 0.46 +/- 0.06 with a dispersion of 0.3, and a maximum value of nu/sigma similar or equal to 1.1. Both rotation and velocity anisotropy contribute significantly in flattening the compact galaxies. Some of the observed compact galaxies appear flatter than any of the simulated galaxies. Finally, it is found that the massive compact galaxies are strongly baryon dominated in their inner parts, with typical dark matter mass fractions of order only 20% inside of r = 2 R-eff.