4 research outputs found
Large scale correlations in galaxy clustering from the Two degree Field Galaxy Redshift Survey
We study galaxy correlations from samples extracted from the 2dFGRS final
release. Statistical properties are characterized by studying the nearest
neighbor probability density, the conditional density and the reduced two-point
correlation function. The result is that the conditional density has a
power-law behavior in redshift space described by an exponent \gamma=0.8 \pm
0.2 in the interval from about 1 Mpc/h, the average distance between nearest
galaxies, up to about 40 Mpc/h, corresponding to radius of the largest sphere
contained in the samples. These results are consistent with other studies of
the conditional density and are useful to clarify the subtle role of
finite-size effects on the determination of the two-point correlation function
in redshift and real spaceComment: 11 pages, 14 figures. Accepted for publication in Astronomy and
Astrophysic
Absence of self-averaging and of homogeneity in the large scale galaxy distribution
The properties of the galaxy distribution at large scales are usually studied
using statistics which are assumed to be self-averaging inside a given sample.
We present a new analysis able to quantitatively map galaxy large scale
structures while testing for the stability of average statistical quantities in
different sample regions. We find that the newest samples of the Sloan Digital
Sky Survey provide unambiguous evidence that galaxy structures correspond to
large amplitude density fluctuations at all scales limited only by sample
sizes. The two-point correlations properties are self-averaging up to
approximately 30 Mpc/h and are characterized by a fractal dimension D=2.1 +-
0.1. Then at all larger scales probed density fluctuations are too large in
amplitude and too extended in space to be self-averaging inside the considered
volumes. These inhomogeneities are compatible with a continuation of fractal
correlations but incompatible with: (i) a homogeneity scale smaller than 100
Mpc/h, (ii) predictions of standard theoretical models, (iii) mock galaxy
catalogs generated from cosmological Nbody simuations.Comment: 6 pages with 4 figures. Some changes to match the accepted version.
To be published in Europhysics Letters (May 2009
Gravitational hydrodynamics of large scale structure formation
The gravitational hydrodynamics of the primordial plasma with neutrino hot
dark matter is considered as a challenge to the bottom-up cold dark matter
paradigm. Viscosity and turbulence induce a top-down fragmentation scenario
before and at decoupling. The first step is the creation of voids in the
plasma, which expand to 37 Mpc on the average now. The remaining matter clumps
turn into galaxy clusters. Turbulence produced at expanding void boundaries
causes a linear morphology of 3 kpc fragmenting protogalaxies along vortex
lines. At decoupling galaxies and proto-globular star clusters arise; the
latter constitute the galactic dark matter halos and consist themselves of
earth-mass H-He planets. Frozen planets are observed in microlensing and
white-dwarf-heated ones in planetary nebulae. The approach also explains the
Tully-Fisher and Faber-Jackson relations, and cosmic microwave temperature
fluctuations of micro-Kelvins.Comment: 6 pages, no figure