Do Galactic Systems Form too Late in Cold + Hot Dark Matter Models?
Abstract
The abundance of galactic systems at high redshifts can impose a strong constraint on the cold + dark matter (CDM + HDM) models. The hot component reduces the excessive smallscale power in the COBEnormalized CDM model but also delays the epoch of galaxy formation. We present results from the first numerical simulations that have enough dynamic range to address accurately the issue of highredshift halo abundances in CDM + HDM models. Equivalent highresolution particleparticle/particle mesh Nbody simulations are performed for spatially flat models with {OMEGA}_{nu}_ = 0.3 and 0.2 (with H_0_ = 50 km s^1^ Mpc^1^ and {OMEGA}_b_ = 0.05). We study the constraints placed on the models by the highredshift quasar space density and by the mass fraction in neutral dense gas associated with damped Lyα systems. We find that even with optimistic assumptions, the muchstudied {OMEGA}_{nu}_ = 0.3 model does not produce enough massive halos to account for the observed abundance of quasars at z > 4. The model passes this test if {OMEGA}_{nu}_ is decreased to 0.2. Both models do not produce enough high column density halos to account for the amount of gas in damped Lyα systems at z >~ 3: the {OMEGA}_{nu}_ = 0.3 model falls short by a factor of ~80; the {OMEGA}_{nu}_ = 0.2 model by a factor ~3. We conclude that only CDM + HDM models with {OMEGA}_{nu}_ <~ 0.2 can match observations at high redshift, implying an upper bound of 4.7 eV on the most massive light neutrino (presumably the τ).
 Publication:

The Astrophysical Journal
 Pub Date:
 October 1994
 DOI:
 10.1086/187559
 arXiv:
 arXiv:astroph/9407085
 Bibcode:
 1994ApJ...434L...5M
 Keywords:

 Abundance;
 Astronomical Models;
 Dark Matter;
 Galactic Evolution;
 Numerical Analysis;
 Absorption Spectra;
 Computational Grids;
 Many Body Problem;
 Quasars;
 Red Shift;
 Astrophysics;
 COSMOLOGY: THEORY;
 COSMOLOGY: DARK MATTER;
 GALAXIES: FORMATION;
 GALAXIES: QUASARS: GENERAL;
 GALAXIES: QUASARS: ABSORPTION LINES;
 Astrophysics;
 High Energy Physics  Phenomenology
 EPrint:
 11 pages including 2 figures, uuencoded compressed postscript, Caltech GRP393