Formation Of Dark Halos Research Articles

Dark energy parametrizations and their effect on dark halos

There are a plethora of dark energy parametrizations that can fit current supernovae Iadata. However, these data are only sensitive to redshifts up to order one. In fact, many ofthese parametrizations break down at higher redshifts. In this paper we study the effect ofdark energy models on the formation of dark halos. We select a couple of dark energyparametrizations which are sensible at high redshifts and compute their effecton the evolution of density perturbations in the linear and non-linear regimes.Using the Press–Schechter formalism we show that they produce distinguishablesignatures in the number counts of dark halos. Therefore, future observations of galaxyclusters can provide complementary constraints on the behaviour of dark energy.

The growth and structure of dark matter haloes

In this paper, we analyse in detail the mass-accretion histories and structural properties of dark haloes in high-resolution N-body simulations. We model the density distribution in individual haloes using the Navarro-Frenk-White (NFW) profile. For a given halo, there is a tight correlation between its inner-scale radius r(s) and the mass within it, M-s, for all its main progenitors. Using this correlation, one can predict quite well the structural properties of a dark halo at any time in its history from its mass-accretion history, implying that the structure properties and the mass-accretion history are closely correlated. The predicted growing rate of concentration c with time tends to increase with decreasing mass-accretion rate. The build-up of dark haloes in cold dark matter (CDM) models generally consists of an early phase of fast accretion (where the halo mass M-h increases with time much faster than the expansion rate of the Universe) and a late phase of slow accretion (where M-h increases with time approximately as the expansion rate). These two phases are separated at a time when c similar to 4 and the typical binding energy of the halo is approximately equal to that of a singular isothermal sphere with the same circular velocity. Haloes in the two accretion phases show systematically different properties, for example, the circular velocity v(h) increases rapidly with time in the fast accretion phase but remains almost constant in the slow accretion phase, the inner properties of a halo, such as r(s) and M-s increase rapidly with time in the fast accretion phase but change only slowly in the slow accretion phase, the inner circular velocity v(s) is approximately equal to v(h) in the fast accretion phase but is larger in the slow accretion phase. The potential well associated with a halo is built up mainly in the fast accretion phase, while a large amount of mass can be accreted in the slow accretion phase without changing the potential well significantly. We discuss our results in connection with the formation of dark haloes and galaxies in hierarchical models.

The Role of Heating and Enrichment in Galaxy Formation

We show that the winds identified with high-redshift low-mass galaxies may strongly affect the formation of stars in more massive galaxies that form later. With 3D realizations of a simple nonlinear growth model we track gas shocking, metal enrichment, and cooling, together with dark halo formation. We show that outflows typically strip baryonic material out of pre-virialized intermediate mass halos, suppressing star formation. More massive halos can trap the heated gas but collapse later, leading to a broad bimodal redshift distribution, with a larger characteristic mass and metallicity associated with the lower redshift peak. This scenario accounts for the observed bell-shaped luminosity function of early-type galaxies, explains the small number of Milky-Way satellite galaxies relative to standard Cold Dark Matter proscriptions, and provides a reasonable explanation for the lack of metal poor stars in the solar neighborhood and the more general lack of low-metallicity stars in other massive galaxies relative to “closed-box” models of chemical enrichment. Heating of the intergalactic medium by early outflows should produce spectral distortions in the cosmic microwave background that will be measurable with the next generation of experiments. Subject headings: galaxies: formation – galaxies: interactions– large-scale structure of the universe – galaxies: elliptical

The formation of dark halos in a universe dominated by cold dark matter

view Abstract Citations (605) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Formation of Dark Halos in a Universe Dominated by Cold Dark Matter Frenk, Carlos S. ; White, Simon D. M. ; Davis, Marc ; Efstathiou, George Abstract We investigate the formation of galactic halos in a flat universe dominated by cold dark matter. The amplitude and scale of the initial fluctuations are set to agree with previous models for the large-scale galaxy distribution. We use gravitational N-body simulations to study cubic regions of present size ~14 Mpc and of varying density. We follow such regions from z = 6 to the present with a linear resolution which decreases from ~2 to ~14 kpc. Halos of galactic scale form abundantly in these models only after z ~ 3. Their early evolution is dominated by mergers, but the merger rate begins to decline after z ~ 1. Although recent mergers are responsible for the most massive of present-day halos, many smaller systems grew in a relatively quiescent fashion after z ~ 0.5. Throughout the central regions of most dark halos the circular velocity is almost independent of radius, predicting a "rotation curve" similar in form to those of spiral galaxies. However, the circular velocities of the most massive systems rise significantly between 50 and 100 kpc. We conjecture that these objects correspond to the massive halos of elliptical galaxies or to the merged halos of small groups. The bulk rotation velocity of halos is typically only about 10% of their velocity dispersion and is roughly independent of radius. Many halos are strongly aspherical with three unequal axes. There is, perhaps, a slight preference for near-prolate shapes. The mass distribution of the halo population is well approximated by a power law of index -2 with a high mass cutoff which grows rapidly with time, especially in high-density regions. If we identify the cumulative mass distribution of dark halos with the cumulative luminosity distribution of galaxies, we are able to reproduce both the form and the amplitude of the Tully-Fisher/Faber-Jackson relation. This match between the predicted abundance of halos and the observed abundance of galaxies is a major success of the model. Massive halos form preferentially in regions of high dark matter density and are thus naturally biased relative to the mass. Their formation sites correspond well to high peaks of the initial linear density field. This bias may be as strong as is required to reconcile a flat universe with the dynamics of observed galaxy systems, but further work is needed to demonstrate this point conclusively. Our models set the stage for galaxy formation in the cold dark matter cosmogony; they suggest explanations for the different morphological types of galaxies, for their differing distributions, and for indications of substantial evolution in galaxy properties at moderate redshift. Publication: The Astrophysical Journal Pub Date: April 1988 DOI: 10.1086/166213 Bibcode: 1988ApJ...327..507F Keywords: Cosmology; Dark Matter; Galactic Evolution; Galactic Structure; Spiral Galaxies; Stellar Luminosity; Astronomical Models; Computational Astrophysics; Galactic Clusters; Morphology; Universe; Astrophysics; COSMOLOGY; DARK MATTER; GALAXIES: FORMATION; GALAXIES: INTERNAL MOTIONS; GALAXIES: STRUCTURE; NUMERICAL METHODS full text sources ADS |