3,458 research outputs found
The Large-Scale Velocity Field
Get PDFI summarize both observational and theoretical developments in the last few
years in measuring and understanding the large-scale velocity field of
galaxies, with special attention to the bulk flow, or average peculiar
velocity, within spheres centered on the Local Group.Comment: 12 pages standard Latex (w/figures). Uses psfig.tex, included. To be
published in ``Critical Dialogues in Cosmology'' ed. Turok. Uses AAS macros,
postscript also available at
http://www.astro.princeton.edu/~library/preprints/pop684.ps.g
Measuring High-Order Moments of the Galaxy Distribution from Counts in Cells -- The Edgeworth Approximation
Get PDFTo probe the weakly non-linear regime, past the point where simple linear
theory is sufficient to describe the statistics of the density distribution, we
measure the skewness (S_3) and kurtosis (S_4) of the Count Probability
Distribution Function (CPDF) of the IRAS 1.2 Jy sample obtained from counts in
cells. These quantities are free parameters in a maximum likelihood fit of an
Edgeworth expansion convolved with a Poissonian to the observed CPDF. This
method, applicable on scales greater than 5 Mpc, is appreciably less sensitive
to the tail of the distribution than are measurements of S_3 and S_4 from
moments of the CPDF. We measure S_3 and S_4 to l~50 h^{-1} Mpc; the data are
consistent with scale invariance, yielding averages of = 2.83 +/- 0.09,
and = 6.89 +/- 0.68. These values are higher than those found using the
moments method on the same data set, = 1.5 +/- 0.5 and = 4.4 +/-
3.7, due to lack of correction in the latter work for finite-volume effects.
Unlike the moments method, our results are quite robust to the fact that IRAS
galaxies are under-represented in cluster cores. We use N-body simulations to
show that our method yields unbiased results.Comment: 31 pages, ApJ, in press, volume 493. Matches published version; more
complete discussion of error
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