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Record 34 of 2088
Testing the gravitational instability hypothesis?
External Online Source: doi:10.1086/174119
Author and Affiliation:
Babul, Arif(Canadian Inst. for Theoretical Astrophysics, Toronto, Ontario, Canada)
Weinberg, David H.(Institute for Advanced Study, Princeton, NJ, United States)
Dekel, Avishai(Hebrew Univ., Jerusalem, Israel)
Ostriker, Jeremiah P.(Princeton Univ., Observatory, Princeton, NJ, United States)
Abstract: We challenge a widely accepted assumption of observational cosmology: that successful reconstruction of observed galaxy density fields from measured galaxy velocity fields (or vice versa), using the methods of gravitational instability theory, implies that the observed large-scale structures and large-scale flows were produced by the action of gravity. This assumption is false, in that there exist nongravitational theories that pass the reconstruction tests and gravitational theories with certain forms of biased galaxy formation that fail them. Gravitational instability theory predicts specific correlations between large-scale velocity and mass density fields, but the same correlations arise in any model where (a) structures in the galaxy distribution grow from homogeneous initial conditions in a way that satisfies the continuity equation, and (b) the present-day velocity field is irrotational and proportional to the time-averaged velocity field. We demonstrate these assertions using analytical arguments and N-body simulations. If large-scale structure is formed by gravitational instability, then the ratio of the galaxy density contrast to the divergence of the velocity field yields an estimate of the density parameter Omega (or, more generally, an estimate of beta identically equal to Omega(exp 0.6)/b, where b is an assumed constant of proportionality between galaxy and mass density fluctuations. In nongravitational scenarios, the values of Omega or beta estimated in this way may fail to represent the true cosmological values. However, even if nongravitational forces initiate and shape the growth of structure, gravitationally induced accelerations can dominate the velocity field at late times, long after the action of any nongravitational impulses. The estimated beta approaches the true value in such cases, and in our numerical simulations the estimated beta values are reasonably accurate for both gravitational and nongravitational models. Reconstruction tests that show correlations between galaxy density and velocity fields can rule out some physically interesting models of large-scale structure. In particular, successful reconstructions constrain the nature of any bias between the galaxy and mass distributions, since processes that modulate the efficiency of galaxy formation on large scales in a way that violates the continuity equation also produce a mismatch between the observed galaxy density and the density inferred from the peculiar velocity field. We obtain successful reconstructions for a gravitational model with peaks biasing, but we also show examples of gravitational and nongravitational models that fail reconstruction tests because of more complicated modulations of galaxy formation.
Publication Date: May 20, 1994
Document ID:
(Acquired Dec 28, 1995)
Accession Number: 95A65720
Subject Category: ASTROPHYSICS
Document Type: Journal Article
Publication Information: Astrophysical Journal, Part 1 (ISSN 0004-637X); 427; 1; p. 1-24
Publisher Information: United States
Contract/Grant/Task Num: NSF PHY-92-45317; NSF AST-91-09103; NAGW-2448
Financial Sponsor: NASA; United States
Organization Source: NASA; Washington, DC, United States
Description: 24p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
Imprint And Other Notes: Astrophysical Journal, Part 1 vol. 427, no. 1 p. 1-24 May 20, 1994
Miscellaneous Notes: Research sponsored by NATO, W. M. Keck Foundation, the Ambrose Monell Foundation, and the US-Israel BSF
Availability Source: Other Sources
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