arXiv subjects

Jon Holtzman

Publications and source records attributed to Jon Holtzman.

94 records · Page 6Linked to original sources

arXiv1994

Cold + Hot Dark Matter Cosmology with $m(ν_μ) \approx m(ν_τ) \approx 2.4$ ev

Cold + Hot Dark Matter (CHDM) $Ω=1$ cosmological models require a total neutrino mass $\sim 5$ eV. Because recent data support the $ν_μ\to ν_τ$ oscillation explanation of the cosmic ray $ν_μ$ deficit, which requires that $m(ν_μ) \approx m(ν_τ)$, this suggests that $m(ν_μ) \approx m(ν_τ) \approx 2.4$ eV. The linear calculations and N-body simulation reported here indicate that an $Ω=1$ CHDM model with two 2.4 eV neutrinos (designated C$ν^2$DM) agrees remarkably well with all available observations, but only if the Hubble parameter $h \approx 0.5$. We also show that even one 2.4 eV neutrino raises serious difficulties for low-$Ω$ flat CDM models.

astro-ph↗

arXiv1994

Damped Lyman Alpha Systems vs. Cold + Hot Dark Matter

Damped Ly$α$ systems provide possibly the most significant evidence for early structure formation, and thus a stringent constraint on the Cold + Hot Dark Matter (CHDM) cosmology. Using the numbers of halos in N-body simulations to normalize Press-Schechter (PS) estimates of the number densities of protogalaxies as a function of redshift, we find that CHDM with $Ω_c/Ω_ν/Ω_b = 0.6/0.3/0.1$ is compatible with the damped Ly$α$ data only at $z<2.5$, but that it is probably incompatible with data at $z>3$. The predictions of CHDM are quite sensitive to the neutrino fraction. We find that $Ω_c/Ω_ν/Ω_b = 0.725/0.20/0.075$ is compatible with the $z>3$ data. With one massive neutrino species, this corresponds to lowering the neutrino mass from 7.0 to 4.7 eV, for $H_0=50\kmsMpc$ and $T=2.726$ K. By analysing our numerical simulations with different resolutions and box sizes as well as those of Ma \& Bertchinger (1994), we show that for the CHDM models with $Ω_ν$=0.2--0.3 the PS approximation should be used with Gaussian filter with $δ_c=1.3-1.4$ if one tries to recover the total mass of a collapsed halo and to include nonlinear effects, due to waves both longer and shorter than those within the simulation box.

astro-ph↗

arXiv1994

Damped Lyman Alpha Systems vs. Cold + Hot Dark Matter

Although the Cold + Hot Dark Matter (CHDM) cosmology provides perhaps the best fit of any model to all the available data at the current epoch, CHDM produces structure at relatively low redshifts and thus could be ruled out if there were evidence for formation of massive objects at high redshifts. Damped Ly$α$ systems are abundant in quasar absorption spectra and thus provide possibly the most significant evidence for early structure formation, and thus perhaps the most stringent constraint on CHDM. Using the numbers of halos in N-body simulations to normalize Press-Schechter estimates of the number densities of protogalaxies as a function of redshift, we find that CHDM with $Ω_c/Ω_ν/Ω_b = 0.6/0.3/0.1$ is compatible with the damped Ly$α$ data at $\le 2.5$, but that it is probably incompatible with the limited $z>3$ damped Ly$α$ data. The situation is uncertain because there is very little data for $z>3$, and also it is unclear whether all damped Ly$α$ systems are associated with collapsed protogalaxies. The predictions of CHDM are quite sensitive to the hot (neutrino) fraction, and we find that $Ω_c/Ω_ν/Ω_b = 0.675/0.25/0.075$ is compatible even with the $z>3$ data. This corresponds to lowering the neutrino mass from 6.8 to 5.7 eV, for $H_0=50\kmsMpc$. In CHDM, the higher redshift damped Ly$α$ systems are predicted to have lower masses, which can be checked by measuring the velocity widths of the associated metal line systems.

astro-ph↗

arXiv1993

Structure Formation with Cold + Hot Dark Matter

We report results from high-resolution particle-mesh (PM) N-body simulations of structure formation in an $Ω=1$ cosmological model with a mixture of Cold plus Hot Dark Matter (C+HDM) having $Ω_{\rm cold}=0.6$, $Ω_ν=0.3$, and $Ω_{\rm baryon}=0.1$. We present analytic fits to the C+HDM power spectra for both cold and hot ($ν$) components, which provide initial conditions for our nonlinear simulations. In order to sample the neutrino velocities adequately, these simulations included six times as many neutrino particles as cold particles. Our simulation boxes were 14, 50, and 200~Mpc cubes (with $H_0=50$ km s$^{-1}$ Mpc$^{-1}$); we also did comparison simulations for Cold Dark Matter (CDM) in a 50~Mpc box. C+HDM with linear bias factor $b=1.5$ is consistent both with the COBE data and with the galaxy correlations we calculate. We find the number of halos as a function of mass and redshift in our simulations; our results for both CDM and C+HDM are well fit by a Press-Schechter model. The number density of galaxy-mass halos is smaller than for CDM, especially at redshift $z>2$, but the numbers of cluster-mass halos are comparable. We also find that on galaxy scales the neutrino velocities and flatter power spectrum in C+HDM result in galaxy pairwise velocities that are in good agreement with the data, and about 30\% smaller than in CDM with the same biasing factor. On scales of several tens of Mpc, the C+HDM streaming velocities are considerably larger than CDM. Thus C+HDM looks promising as a model of structure formation.

astro-ph↗