Page 1 of 1

[1007.1860] Gravitational fluctuations of the galaxy distri

Posted: July 29 2010
by Syksy Rasanen
The large difference between the statistical properties of galaxies in observations and simulations has previously been analysed using the fractal dimension, see http://cosmocoffee.info/viewtopic.php?t=1543. Simply put, [tex]\Lambda[/tex]CDM simulations are much more homogeneous than the observations.

This paper compares the probability distribution function of the (regularised) Newtonian force in SDSS DR7 and the Millennium simulation semi-analytic galaxy catalog. The difference in the matter distribution is of course reflected in the force. In simulations, the force stabilises beyond few tens of Mpc, whereas for the observations, the force does not converge up to scales of 80-100 Mpc/h, in agreement with previous analyses using different methods (astro-ph/0510106, 0810.3658).

The author notes that, assuming that peculiar velocity is parallel to the gravitational acceleration, the forces calculated from observations are compatible with the claimed large bulk flows (see e.g. 0809.3734, 0910.4958, 0911.5516, 1001.1261). Such large flows are (like the observed statistical properties of the galaxy distribution) unexpected in a vanilla [tex]\Lambda[/tex]CDM universe. (I should say, though, that the role of systematics in the bulk flow analyses is not clear to me: in one method, you have to put together different catalogs, and in the other, remove the cosmological CMB signal from the maps to see the kinetic SZ effect.)