High-Energy Astrophysics American and Soviet Perspectives/Proceedings from the U.S.-U.S.S.R. Workshop on High-Energy Astrophysics (1991) / Chapter Skim
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THE PECULIAR VELOCITY FIELD PREDICTED FROM THE DISTRIBUTION OF IRAS GALAXIES
THE PECULIAR VELOCITY FIELD PREDICTED FROM THE DISTRIBUTION OF IRAS GALAXIES
Pages 356-367
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From page 356... ...
After briefly describing our sample selection and observations, we use the linear theory relation between acceleration and peculiar velocity to make predictions of the peculiar velocity field in the Local Universe. We compare our predictions with directly measured peculiar velocities from the Local Supercluster spiral galaxy sample of Aaronson et al.
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From page 357... ...
Because of the full-sly coverage and the lack of Galactic extinction in the far-infrared, the {RAS database offers a unique opportunity to study the large-scale distribution of galaxies. We have selected galaxy candidates hom the IRAS Point Source Catalog (1985)
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From page 358... ...
~/''~"-'* ~ ~ A 2539 OBJECTS PLO ~ i Ed `~~ ~:'~'~ 360 FIGURE 1 Me distribution of galaxies in the surrey, plotted in Galactic coordinates.
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From page 359... ...
and the process is repeated until convergence. Q is kept fixed throughout this procedure, and the value of V[,G used is that derived Mom the IRAS sample itself on each iteration A "buffer zone" between 8,000 km s~: and 10,000 An s~i prevents galaxies from being lost from the sample if their peculiar velocities take them beyond 8,000 An sol.
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From page 360... ...
, and the independent peculiar velocities of individual galaxies, groups, and clusters of the Seven Samurai elliptical galaxy sample, listed In Table 4 of Faber et al.
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From page 361... ...
In Figure 3, the same compar~son of observed and predicted peculiar velocities is made, this time in a frame at rest with respect to the Local
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From page 362... ...
Note now in panel (d) that the sense of an overall bunk flow to the residuals between observed and predicted peculiar velocities has vanished, and we are left with mostly small-scale motions that we have not modelled correctly.
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From page 363... ...
We emphasize that the motivation is not so much to test the Cold Dark Matter cosmogony, but rather to test our iteration scheme of peculiar velocities in the presence of non-linear erects and shot noise. A total of 18 realizations were run: nine with different "Local Groups," and nine more with a single "Local Group," but different random numbers selecting the galaxies in the suney.
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From page 364... ...
The true peculiar velocities were perturbed by a gaussian "error" with a standard deviation of 15% of the true distance to mimic the observational situation. Unlike the real observations, we assume here that the distances are measured exactly.
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From page 365... ...
t ~_ _ t · `. I I I `1' 1- -4000-2000 0 2000 4000 -4000-2000 0 2000 4000 FIGURE 5 The results of an N-body experiment simulating the comparison between obsenred and predicted peculiar velocities.
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From page 366... ...
Detailed calculations of the noise in the acceleration of galaxies relative to the Local Group is consistent with the observed amplitude of the effect, which must be at least partly responsible for the missing bunk motions seen in the predicted velocity field of the real IRAS galaxies. UNRESOLVED ISSUES, AND THE WORK AEIEAD In the last section, we have identified shot noise as a stumbling block in the interpretation of the comparison of our predictions with observations.
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From page 367... ...
(eds.~. Large Scale Motions in the Universe: A Vatican Study Weed Princeton University Press, Princeton.
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