8 research outputs found
Breaking the self-averaging properties of spatial galaxy fluctuations in the Sloan Digital Sky Survey - Data Release Six
Statistical analyses of finite sample distributions usually assume that
fluctuations are self-averaging, i.e. that they are statistically similar in
different regions of the given sample volume. By using the scale-length method,
we test whether this assumption is satisfied in several samples of the Sloan
Digital Sky Survey Data Release Six. We find that the probability density
function (PDF) of conditional fluctuations, filtered on large enough spatial
scales (i.e., r>30 Mpc/h), shows relevant systematic variations in different
sub-volumes of the survey. Instead for scales r<30 Mpc/h the PDF is
statistically stable, and its first moment presents scaling behavior with a
negative exponent around one. Thus while up to 30 Mpc/h galaxy structures have
well-defined power-law correlations, on larger scales it is not possible to
consider whole sample average quantities as meaningful and useful statistical
descriptors. This situation is due to the fact that galaxy structures
correspond to density fluctuations which are too large in amplitude and too
extended in space to be self-averaging on such large scales inside the sample
volumes: galaxy distribution is inhomogeneous up to the largest scales, i.e. r
~ 100 Mpc/h, probed by the SDSS samples. We show that cosmological corrections,
as K-corrections and standard evolutionary corrections, do not qualitatively
change the relevant behaviors. Finally we show that the large amplitude galaxy
fluctuations observed in the SDSS samples are at odds with the predictions of
the standard LCDM model of structure formation.(Abridged version).Comment: 32 pages, 28 figures, accepted for publication in Astronomy and
Astrophysics. A higher resolution version is available at
http://pil.phys.uniroma1.it/~sylos/fsl_highlights.html . Version v2 has been
corrected to match the published on
Scale-invariance of galaxy clustering
Some years ago we proposed a new approach to the analysis of galaxy and
cluster correlations based on the concepts and methods of modern statistical
Physics. This led to the surprising result that galaxy correlations are fractal
and not homogeneous up to the limits of the available catalogs. The usual
statistical methods, which are based on the assumption of homogeneity, are
therefore inconsistent for all the length scales probed so far, and a new, more
general, conceptual framework is necessary to identifythe real physical
properties of these structures. In the last few years the 3-d catalogs have
been significatively improved and we have extended our methods to the analysis
of number counts and angular catalogs. This has led to a complete analysis of
all the available data that we present in this review. The result is that
galaxy structures are highly irregular and self-similar: all the available data
are consistent with each other and show fractal correlations (with dimension ) up to the deepest scales probed so far (1000 \hmp) and even more
as indicated from the new interpretation of the number counts. The evidence for
scale-invariance of galaxy clustering is very strong up to 150 \hmp due to
the statistical robustness of the data but becomes progressively weaker
(statistically) at larger distances due to the limited data. In These facts
lead to fascinating conceptual implications about our knowledge of the universe
and to a new scenario for the theoretical challenge in this field.Comment: Latex file 165 pages, 106 postscript figures. This paper is also
available at http://www.phys.uniroma1.it/DOCS/PIL/pil.html To appear in
Physics Report (Dec. 1997