Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · astro-ph/0104417

The pair-wise velocity dispersion of galaxies: effects of non radial motions

A. Del Popolo
View original source ↗Read source document ↗Export metadata ↓

Abstract

I discuss the effect of non-radial motions on the small-scale pairwise peculiar velocity dispersions of galaxies (PVD) in a CDM model. I calculate the PVD for the SCDM model by means of the refined cosmic virial theorem (CVT) (Suto & Jing 1997) and taking account of non-radial motions by means of Del Popolo & Gambera (1998) model. I compare the results of the present model with the data from Davis & Peebles (1983), the IRAS value at 1 h{-1} Mpc of Fisher et al. (1993) and Marzke et al. (1995). I show that while the SCDM model disagrees with the observed values, as pointed out by several authors (Peebles 1976, 1980; Davis & Peebles 1983; Mo et. al 1993; Jing et al. 1998), taking account of non-radial motions produce smaller values for the PVD. At r <=1 h^{-1} Mpc the result is in agreement with Bartlett & Blanchard (1996) (hereafter BB96). At the light of this last paper, the result may be also read as a strong dependence of the CVT prediction on the model chosen to describe the mass distribution around galaxies, suggesting that the CVT cannot be taken as a direct evidence of a low density universe. Similarly to what shown in Del Popolo & Gambera (1999, 2000) (hereafter DG99, DG00), Del Popolo et al. (1999), the agreement of our model to the observational data is due to a scale dependent bias induced by the presence of non-radial motions. Since the assumptions on which CVT is based have been questioned by several authors (BB96; SJ97), I also calculated the PVD using the redshift distortion in the redshift-space correlation function, ξ_z(r_p,π), and I compared it with the PVD measured from the Las Campanas Redshift Survey by J98. The result confirms that non-radial motions influence the PVD making them better agree with observed data.

Explore related subjects

astro-ph

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

A. Del Popolo. 2001-04-25. The pair-wise velocity dispersion of galaxies: effects of non radial motions. https://doi.org/10.1046/j.1365-8711.2001.04621.x

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2023

Dark Energy is the Cosmological Quantum Vacuum Energy of Light Particles-The Axion and the Lightest Neutrino

We uncover the general mechanism producing the dark energy(DE). This is only based on well known quantum physics and cosmology. We show that the observed DE originates from the cosmological quantum vacuum of light particles which provides a continuous energy distribution able to reproduce the data. Bosons give positive contributions to the DE while fermions yield negative contributions. As usual in field theory, ultraviolet divergences are subtracted from the physical quantities. The subtractions respect the symmetries of the theory and we normalize the physical quantities to be zero for the Minkowski vacuum. The resulting finite contributions to the energy density and the pressure from the quantum vacuum grow as log a(t) where a(t) is the scale factor, while the particle contributions dilute as 1/a^3(t), as it must be for massive particles. The DE equation of state P = w(z)H turns to be w(z)<-1 with w(z) asymptotically reaching the value -1 from below.A scalar particle can produce the observed DE through its quantum cosmological vacuum provided:(i)its mass is of the order of 10^{-3} eV = 1 meV,(ii) it is very weakly coupled and (iii) it is stable on the time scale of the age of the universe. The axion vacuum thus appears as a natural candidate. The neutrino vacuum (especially the lightest mass eigenstate) can give negative contributions to the DE. We find that w(z=0) is slightly below -1 by an amount ranging from [-1.5 10^{-3}] to [-8 10^{-3}] and we predict the axion mass to be in the range between 4 and 5 meV. We find that the universe will expand in the future faster than the de Sitter universe, as an exponential in the square of the cosmic time. DE arises from the quantum vacua of light particles in FRW cosmological space time in an analogous way to the Casimir effect in Minkowski spacetime with non trivial boundaries.

astro-ph↗
arXiv2023

Scaling of Black Hole Accretion Discs from Gamma-Ray Bursts and Black Hole X-Ray Binaries to Active Galactic Nuclei

I consider how physical processes scale over eight orders of magnitude in black hole mass, from stellar masses in gamma-ray bursts (GRB) and black-hole X-ray binaries (BHXRB) to supermassive active galactic nuclei (AGN). Accretion rates onto stellar mass black holes range over more than sixteen orders of magnitude, from the lower luminosity BHXRB to GRB. These enormous parameter ranges correspond to qualitative as well as quantitative differences in behavior. The fundamental questions involve the balance between nonequilibrium and thermalized plasmas. When energy fluxes exceed a critical value $\sim 10^{29}$ erg/cm$^2$s, as in GRB, a black-body equilibrium pair plasma forms. At the lower fluxes found in AGN, BHXRB and microquasars, accretion power electrodynamically accelerates a small number of very energetic particles, explaining their non-thermal spectra and the high energy gamma-ray emission of blazars. Ultra-high energy cosmic rays may be accelerated by massive black holes, otherwise undetectable, with very low thermal luminosities. New-born fast high-field pulsars may be in the black-body equilibrium regime, resembling SGR in permanent outburst. I also consider the question, significant for the acceleration of nonthermal particles in GRB outflows, of whether collisionless plasmas interpenetrate rather than forming hydrodynamic shocks, and propose this as an alternative to internal shock models of GRB. A new appendix attempts to explain why AGN are, proportionally, more efficient accelerators of energetic particles than stellar mass black holes.

astro-ph↗