Formation of subgalactic objects within two-component dark matter

Journal Article · Sun Dec 15 04:00:00 EST 1985 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/163726· OSTI ID:5961681

Umemura, M; Ikeuchi, S

We consider the Einstein--de Sitter universe dominated by two kinds of collisionless relics: neutrinos as hot dark matter, and X particles having negligible thermal velocity as cold dark matter (CDM). We assume ..cap omega../sub v/>..cap omega../sub c/> or =..cap omega../sub b/ = 0.05, which is referred to as the hybrid model. On scales larger than that of neutrino collisionless damping, neutrino fluctuations develop with time, producing large-scale neutrino overdense (NOD) and underdense (NUD) regions which evolve consequently to superclusters and huge voids, respectively. We calculate the growth of fluctuations of CDM and induced fluctuations of baryons on subgalactic scales in the NOD and NUD regions from the recombination epoch to the present. CDM fluctuations on subgalactic scales can grow faster in the NOD region than in the NUD region. It is shown that dwarf galaxies are preferably formed in NOD regions, induced by CDM potential wells; and subgalactic baryon fluctuations in NUD regions are subject to UV heating by QSOs before collapse and converted to expanding clouds unclustered in voids. These clouds are favorable candidates for Ly..cap alpha.. absorbers with just the same neutral hydrogen column density as observed, irrespective of ..cap omega../sub c/. This scenario for the formation of subgalactic objects is successful if 0.15< or =..cap omega../sub c/< or =0.35, and correspondingly 0.8> or =..cap omega../sub v/> or =0.6, assuming the constant curvature spectrum. It is another characteristic of the hybrid model that ordinary galaxies, including QSOs, are formed early from aggregations of dwarfs; and some galaxies can be born in voids in an environment of few dwarfs after the birth of galaxies in NOD regions.

• Research Organization: Department of Physics, Hokkaido University; and Tokyo Astronomical Observatory
• OSTI ID: 5961681
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 299:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
640106 -- Astrophysics &amp; Cosmology-- Cosmology
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BARYONS
COSMIC RADIO SOURCES
COSMOLOGICAL MODELS
DIFFERENTIAL EQUATIONS
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
EQUATIONS
EQUATIONS OF MOTION
EXPANSION
FERMIONS
FLUCTUATIONS
FUNDAMENTAL CONSTANTS
GALACTIC EVOLUTION
GALAXY CLUSTERS
GRAVITATIONAL COLLAPSE
HADRONS
HEATING
LEPTONS
MASSLESS PARTICLES
MATHEMATICAL MODELS
MATHEMATICS
NEUTRINOS
NUMERICAL ANALYSIS
PARTIAL DIFFERENTIAL EQUATIONS
QUASARS
RADIATIONS
ULTRAVIOLET RADIATION
UNIVERSE
VARIATIONS