We use a series of high-resolution N-body simulations of a `Milky-Way' halo, coupled to semi-analytic techniques, to study the formation of our own Galaxy and of its stellar halo. Our model Milky Way galaxy is a relatively young system whose physical properties are in quite good agreement with observational determinations. In our model, the stellar halo is mainly formed from a few massive satellites accreted early on during the galaxy's lifetime. The stars in the halo do not exhibit any metallicity gradient, but higher metallicity stars are more centrally concentrated than stars with lower abundances. This is due to the fact that the most massive satellites contributing to the stellar halo are also more metal rich, and dynamical friction drags them closer to the inner regions of the host halo.
Aims: We want to investigate the growth of bar instability in stellar disks embedded in a suitable dark matter halo evolving in a fully consistent cosmological framework. Methods: We perform seven cosmological simulations to emphasise the role of both the disk-to-halo mass ratio and of the Toomre parameter, Q, on the evolution of the disk.We also compare our fully cosmological cases with corresponding isolated simulations where the same halo, is extracted from the cosmological scenario and evolved in physical coordinates. Results: A long living bar, lasting about 10 Gyr, appears in all our sim…
We investigate how the survival of dark matter satellites inside virialized halos depends on tidal stripping and dynamical friction. We use an analytic approach and then compare the results with N-Body simulations. Both the satellites and the primary halos are similar to cosmological haloes and have NFW density profiles. Satellites can either merge with the primary halo or continue to move on barely perturbed orbits, eventually being disrupted, depending on the relative strength of friction and tidal forces. We propose that their actual fate depends simply on their mass ratio relative to the p…
The gravitational lensing properties of cosmological halos depend upon the mass distribution within each halo. The description of halos as nonsingular, truncated isothermal spheres, a particular solution of the isothermal Lane- Emden equation (suitably modified for Lambda non equal 0), has proved to be a useful approximation for the halos which form from realistic initial conditions in a CDM universe. We derive here the basic lensing properties of such halos, including the image separation, magnification, shear, and time-delay. We also provide analytical expressions for the critical curves and…
We investigate the cosmological Fisher information in the non-linear dark-matter power spectrum in the context of the halo model. We find that there is a plateau in information content on translinear scales which is generic to all cosmological parameters we tried. There is a rise in information on smaller scales, but we find that it is quite degenerate among different cosmological parameters (except, perhaps, the tilt). This suggests that it could be difficult to constrain cosmological parameters using the non-linear regime of the dark-matter power spectrum. We suggest ways to get around this …
We present an analysis of the behaviour of the `coarse-grained' (`mesoscopic') rank partitioning of the mean energy of collections of particles composing virialized dark matter halos in a Lambda-CDM cosmological simulation. We find evidence that rank preservation depends on halo mass, in the sense that more massive halos show more rank preservation than less massive ones. We find that the most massive halos obey Arnold's theorem (on the ordering of the characteristic frequencies of the system) more frequently than less massive halos. This method may be useful to evaluate the coarse-graining le…
Seven cosmological hydrodynamic simulations of disk galaxy formation are analyzed to determine the alignment of the disk within the dark matter halo and the internal structure of the halo. We find that the orientation of the outer halo, beyond ~0.1 r_vir, is unaffected by the presence of the disk. In contrast, the inner halo is aligned such that the halo minor axis aligns with the disk axis. The relative orientation of these two regions of the halo are uncorrelated. The alignment of the disk and inner halo appears to take place simultaneously through their joint evolution. The disconnect betwe…
We have derived an analytical model for the postcollapse equilibrium structure of cosmological halos as nonsingular truncated isothermal spheres (TIS) and compared this model with observations and simulations of cosmological halos on all scales. Our model is in good agreement with the observations of the internal structure of dark-matter-dominated halos from dwarf galaxies to X-ray clusters. It reproduces many of the average properties of halos in CDM simulations to good accuracy, including the density profiles outside the central region, while avoiding the possible discrepancy at small radii …
A new model for the postcollapse equilibrium structure of virialized objects which condense out of the cosmological background universe is described and compared with observations and simulations of cosmological halos from dwarf galaxies to X-ray clusters. The model is based upon the assumption that virialized halos are isothermal, which leads to a prediction of a unique nonsingular isothermal sphere for the equilibrium structure, with a core radius which is approximately 1/30 times the size and a core density which is proportional to the mean background density at the epoch of collapse. These…
An analytical model for the postcollapse equilibrium structure of virialized objects which condense out of the cosmological background universe is described and compared with observations and simulations of cosmological halos. The model is based upon the assumption that virialized halos are isothermal, which leads to a prediction of a unique nonsingular isothermal sphere for the equilibrium structure, with a core density which is proportional to the mean background density at the epoch of collapse. These predicted nonsingular isothermal spheres are in good agreement with observations of the in…
In this study we show how errors due to finite box size affect formation and destruction rate for haloes in cosmological N-body simulations. In an earlier study we gave an analytic prescription of finding the corrections in the mass function. Following the same approach, in this paper we give analytical expressions for corrections in the formation rate, destruction rate and the rate of change in comoving number density, and compute their expected values for the power law ($n=-2$) and LCDM models.
Adaptive SPH and N-body simulations were carried out to study the evolution of the equilibrium structure of dark matter halos that result from the gravitational instability and fragmentation of cosmological pancakes. Such halos resemble those formed by hierarchical clustering from realistic initial conditions in a CDM universe and, therefore, serve as a test-bed model for studying halo dynamics. The dark matter density profile is close to the universal halo profile identified previously from N-body simulations of structure formation in CDM, with a total mass and concentration parameter which g…
We study the growth of galactic disks in live triaxial DM halos. The halos have been assembled through constrained realizations method and evolved from the linear regime using cosmological simulations. The `seed' disks have been inserted at redshift z=3 and increased in mass tenfold over various time periods, ~1-3 Gyr, with the halo responding quasi-adiabatically to this process. We follow the dynamical and secular evolution of the disk-halo system and analyze changes in the most important parameters, like 3-D DM shapes, stellar and DM radial density profiles, stellar bar development, etc. We …
We present an analytic model for the fully nonlinear power spectrum P and bispectrum Q of the cosmological mass density field. The model is based on physical properties of dark matter halos, with the three main model inputs being analytic halo density profiles, halo mass functions, and halo-halo spatial correlations, each of which has been well studied in the literature. We demonstrate that this new model can reproduce the power spectrum and bispectrum computed from cosmological simulations of both an n=-2 scale-free model and a low-density cold dark matter model. To enhance the dynamic range …
Measurements of the linear power spectrum of galaxies have placed tight constraints on neutrino masses. We extend the framework of the halo model of cosmological nonlinear matter clustering to include the effect of massive neutrino infall into cold dark matter (CDM) halos. The magnitude of the effect of neutrino clustering for three degenerate mass neutrinos with m_nu=0.9 eV is of order ~1%, within the potential sensitivity of upcoming weak lensing surveys. In order to use these measurements to further constrain--or eventually detect--neutrino masses, accurate theoretical predictions of the no…
We explore the growth and the evolution of the bar instability in stellar-gaseous disks embedded in a suitable dark matter halo evolving in a fully consistent cosmological framework. The aim of this paper is to point out the impact of different gas fractions on the bar formation, inside disks of different disk-to-halo mass ratio, and the role of the cosmological framework. We perform cosmological simulations with the same disk-to-halo mass ratios as in a previous work where the gas was not taken into account. We compare results of the new simulations with the previous ones to investigate the e…
We present preliminary results from a series of high-resolution N-body simulations that focus on 8 dark matter halos each of order a million particles within the virial radius. We follow the time evolution of hundreds of individually tracked satellite galaxies and relate their physical properties to the differing halo environmental conditions. Our main science driver is to understand how satellite galaxies lose their mass and react to tidal stripping. Unlike previous work our results are performed in a fully self-consistent cosmological context. The preliminary results demonstrate that while e…
We present the first study on the mass functions of Jenkins et al (J01) and an estimate of their corresponding largest virialized dark halos in the Universe for a variety of dark-energy cosmological models with a running spectral index. Compared with the PL-CDM model, the RSI-CDM model can raise the mass abundance of dark halos for small mass halos at lower redshifts, but it is not apparent on scales of massive mass halos. Particularly, this discrepancy increases largely with the decrease of redshift, and the RSI-CDM model can suppress the mass abundance on any scale of halo masses at higher r…
Aims: We investigate the cosmological growth of dark halos and follow the consequences of coeval growth for the accretion history of associated supermassive black holes. Methods: The Press-Schechter approximation is used to obtain an analytic expression for the mean rate of growth of dark matter halos. Dark halo accretion rates are compared with numerical work and the consequences for understanding AGN evolution are described. Results: The mean accretion rate onto dark matter halos is shown to have a simple analytic form that agrees with previous numerical work and that may easily be calculate…
If gamma ray burst sources are in the galactic halo they inevitably involve a creation of an opaque pair plasma fireball, just like in cosmological sources. We find that the typical physical conditions in a galactic halo fireball are: optical depth $\ap 10^8$, thermal energy $\ap 100 KeV$, maximal relativstic expansion $\G \ap 300 $ and a maximal baryonic load of $\ap 10^{-15} M_\odot$. This does not rule out galctic halo models but it poses an addtional severe constraint on all such sources. A comparison of these conditions with the physical conditions at cosmological fireballs reveal that ga…
We perform detailed comparison of the semi-analytic halo model predictions with measurements in numerical simulations of the two and three point correlation functions (3PCF), as well as power spectrum and bispectrum. We discuss the accuracy and self-consistency of the halo model description of gravitational clustering in the non-linear regime and constrain halo model parameters. We exploit the recently proposed multipole expansion of three point statistics that expresses rotation invariance in the most natural way. This not only offers technical advantages by reducing the integrals required fo…
Adaptive SPH and N-body simulations were carried out to study the collapse and evolution of dark matter halos that result from the gravitational instability and fragmentation of cosmological pancakes. Such halos resemble those formed by hierarchical clustering in a CDM universe and serve as a convenient test-bed model for studying halo dynamics. Our halos are in approximate virial equilibrium and roughly isothermal, as in CDM simulations. Their density profiles agree quite well with the fit to N-body results for CDM halos by Navarro, Frenk, & White (NFW). This test-bed model enables us to stud…
Very recent observations of the Li6 isotope in halo stars reveal a Li6 plateau about 1000 times above the predicted BBN abundance. We calculate the evolution of Li6 versus redshift generated from an initial burst of cosmological cosmic rays (CCRs) up to the formation of the Galaxy. We show that the pregalactic production of the Li6 isotope can account for the Li6 plateau observed in metal poor halo stars without additional over-production of Li7. The derived relation between the amplitude of the CCR energy spectra and the redshift of the initial CCR production puts constraints on the physics a…
The recently observed bright optical transients(OT) of high redshift GRBs indicate that they are in a violent dynamical state. We think it is reasonable to assume that the GRBs form in the environment of gravitationally collapsed halos of the cosmic matter field, and we investigate the basic parameters of the halos which are favored to host GRBs. If the harboring coefficient $f$ of GRBs per halo is weakly dependent on the mass of the halo, the redshift data of GRB OTs can yield significant constraints on the massive halos hosting GRBs. We show that, in the framework of popular cold dark matter…
High-resolution N--body simulations show a remarkable similarity in the structure of dark matter halos formed through dissipationless hierarchical clustering. Independent of halo mass, power spectrum, and cosmological parameters, the density profiles of dark halos can be accurately fit by scaling a simple two-parameter profile. The two parameters of the fit, which can be expressed as the mass and characteristic density of each halo, are strongly correlated. The characteristic density is directly proportional to the mean density of the universe at the time of assembly of each halo. Low mass hal…
Using cosmological N-body simulations, we investigate the influence of the matter density parameter Omega_m and the linear theory power spectrum P(k) on statistical properties of the dark matter halo population -- the mass function n(M), the halo correlation function, and halo pairwise velocity statistics. For fixed P(k), the effect of changing Omega_m is simple: the halo mass scale M_* shifts in proportion to Omega_m, pairwise velocities (at fixed M/M_*) are proportional to Omega_m^{0.6}, and halo clustering at fixed M/M_* is unchanged. If one simultaneously changes the P(k) amplitude sigma_8…
We investigate the nonlinear two- and three-point correlation functions of the cosmological density field in Fourier space and test the popular hierarchical clustering model, that the three-point amplitude Q is independent of scale. In high-resolution N-body simulations of both n=-2 scale-free and cold dark matter models, we find that Q at late times is not constant but increases with wavenumber far into the nonlinear regime. Self-similar scaling also does not hold as rigorously for the three-point function as for the two-point function in the n=-2 simulation, perhaps a manifestation of the fi…
We study the formation and evolution of the dark matter halos in a LCDM model. The dynamics of 16.8 million DM particles is followed numerically in a box of 60 Mpc/h with the dynamic range of 32,000 in spatial resolution. The high resolution of the simulation allows us to examine evolution of both isolated and satellite halos in a representative volume. We present results on the evolution of velocity function of DM halos, compare it with the Press-Schechter function and discuss the evolution of power spectrum of matter and halo distributions. The mass evolution of isolated virialized objects d…
Current data suggest that the central mass densities $ρ_0$ and phase-space densities $Q\equivρ_0/σ_V^3$ of cosmological halos in the present universe are correlated with their velocity dispersions $σ_V$ over a very wide range of $σ_V$ from less than 10 to more than 1000 $\rm km s^{-1}$. Such correlations are an expected consequence of the statistical correlation of the formation epochs of virialized objects in the CDM model with their masses; the smaller-mass halos typically form first and merge to form larger-mass halos later. We have derived the $Q-σ_V$ and $ρ_0-σ_V$ correlations for differe…
In Loeb & Rybicki (1999; paper I) it was shown that before reionization, the scattering of \lya photons from a cosmological source might lead to a fairly compact ($\sim 15''$) \lya halo around the source. Observations of such halos could constrain the properties of the neutral intergalactic medium (IGM), and in particular yield the cosmological density parameters of baryons and matter on scales where the Hubble flow is unperturbed. Paper I did not treat the polarization of this scattered radiation, but did suggest that the degree of such polarization might be large. In this Letter we report on…
This is the third of a series of papers presenting the first attempt to analyze the growth of the bar instability in a consistent cosmological scenario. In the previous two articles we explored the role of the cosmology on stellar disks, and the impact of the gaseous component on a disk embedded in a cosmological dark matter halo. The aim of this paper is to point out the impact of the star formation on the bar instability inside disks having different gas fractions. We perform cosmological simulations of the same disk-to-halo mass systems as in the previous works where the star formation was …
We present a statistical analysis of the interactions between satellite galaxies in cosmological dark matter halos taken from fully self-consistent high-resolution simulations of galaxy clusters. We show that the number distribution of satellite encounters has a tail that extends to as many as 3-4 encounters per orbit. On average 30% of the substructure population had at least one encounter (per orbit) with another satellite galaxy. However, this result depends on the age of the dark matter host halo with a clear trend for more interactions in younger systems. We also report a correlation betw…
We report on the results of a search for an intergalactic X-ray dust scattering halo in a deep observation of the bright, high-redshift quasar QSO 1508+5714 with the Chandra X-ray Observatory. We do not detect such a halo. Our result implies an upper limit on the density of diffuse, large-grained intergalactic dust of Omega_ dust < 2 x 10^-6, assuming a characteristic grain size of 1micron. The result demonstrates the sensitivity of this technique for detecting very small amounts of intergalactic dust which are very hard to detect otherwise. This will allow us to put important constraints on s…
We perform an extensive analysis of nonlinear and stochastic biasing of galaxies and dark halos in spatially flat low-density CDM universe using cosmological hydrodynamic simulations. We compare their biasing properties with the predictions of an analytic halo biasing model. Dark halos in our simulations exhibit reasonable agreement with the predictions only on scales larger than 10h^{-1}Mpc, and on smaller scales the volume exclusion effect of halos due to their finite size becomes substantial. Interestingly the biasing properties of galaxies are better described by extrapolating the halo bia…
Density profiles of cosmological virialized systems, or dark halos, have recently attracted much attention. I first present a brief historical review of numerical simulations to quantify the halo density profiles. Then I describe the latest results on the universal density profile and their observational confrontation. Finally I discuss a clustering model of those halos with particular emphasis on the cosmological light-cone effect.
The cooling of gas in the centers of dark matter halos is expected to lead to a more concentrated dark matter distribution. The response of dark matter to the condensation of baryons is usually calculated using the model of adiabatic contraction, which assumes spherical symmetry and circular orbits. In contrast, halos in the hierarchical structure formation scenarios grow via multiple violent mergers and accretion along filaments, and particle orbits in the halos are highly eccentric. We study the effects of the cooling of gas in the inner regions of halos using high-resolution cosmological si…
Theoretical studies and current observations of the high-redshift intergalactic medium (IGM) indicate that at least two cosmic transitions occur by the time the universe reaches gas metallicities of about $10^{-3}$ of solar values. These are the cosmological reionization of the IGM, and the transition from a primordial to present-day mode of star formation. We quantify this relation through new calculations of the ionizing radiation produced in association with the elements carbon, oxygen and silicon observed in Galactic metal-poor halo stars, which are likely second-generation objects formed …
We present a detailed analysis of the velocity distribution and orientation of orbits of subhaloes in high resolution cosmological simulations of dark matter haloes. We find a trend for substructure to preferentially revolve in the same direction as the sense of rotation of the host halo: there is an excess of prograde satellite haloes. Throughout our suite of nine host haloes (eight cluster sized objects and one galactic halo) there are on average 59% of the satellites corotating with the host. Even when including satellites out to five virial radii of the host, the signal still remains point…
We use a series of high-resolution simulations of a `Milky-Way' halo coupled to semi-analytic methods to study the formation of our own Galaxy and of its stellar halo. The physical properties of our model Milky Way, as well as the age and metallicity distribution of stars in the different components, are in relatively good agreement with observational measurements. Assuming that the stellar halo builds up from the cores of the satellite galaxies that merged with the Milky Way over its life-time, we are able to study the physical and structural properties of this component. In agreement with pr…
We present numerical simulations of primordial supernovae in cosmological minihalos at $z \sim$ 20. We consider Type II supernovae, hypernovae, and pair instability supernovae (PISN) in halos from 6.9 $\times$ 10$^5$ - 1.2 $\times$ 10$^7$ $\Ms$, those in which Population III stars are expected to form via H$_2$ cooling. The supernovae evolve along two evolutionary paths according to whether they explode in \ion{H}{2} regions or neutral halos. Those in \ion{H}{2} regions first expand adiabatically and then radiate strongly upon collision with baryons ejected from the halo during its photoevapor…
We quantify the degree of nonlinearity and stochasticity of the clustering of biased objects, using cosmological N-body simulations. Adopting the peaks and the halos as representative biasing models, we focus on the two-point correlation of the biased objects, dark matter and their cross-correlation. Especially, we take account of the effect of redshift-space distortion and attempt to clarify the scale-dependence and the time-dependence by analyzing the biasing factor and the cross-correlation factor. On small scales, stochasticity and nonlinearity become appreciable and strongly object-depend…
[Abridged] We analyze the exchange of dark matter between halos, subhalos, and their environments in a high-resolution cosmological N-body simulation of a Lambda CDM cosmology. At each analyzed redshift z we divide the dark matter particles into 4 components: (i) isolated galactic halos, (ii) subhalos, (iii) the diffuse medium of group and cluster halos, and (iv) the background outside of virialized halos. We follow the time evolution of the mass distribution and flows between these components and provide fitting functions for the exchange rates. We use our derived exchange rates to gauge the …
The formation and structure of dark matter (DM) halos is studied by means of constrained realizations of Gaussian fields using N-body simulations. A series of experiments of the formation of a 10^{12} Msun halo is designed to study the dependence of the density profile on its merging history. We confirm that the halo growth consists of violent and quiescent phases, with the density well approximated by the Navarro-Frenk-White (NFW) profile during the latter phases. We find that (1) the NFW scale radius R_s stays constant during the quiescent phase and grows abruptly during the violent one. In …
Gas rich sub-galactic halos with mass Mt <= 10^7.5 Msun, while incapable of forming stars due to lack of adequate coolants, contain a large fraction of baryonic mass at cosmological reionization. We show that the reionization of the universe at z=10-20 has an interesting physical effect on these halos. The external radiation field causes a synchronous inward propagation of an ionization front towards each halo, resulting in an inward, convergent shock. The resident gas of mass Mb~10^4-10^7 Msun in low spin (initial dimensionless spin parameter lambda <= 0.01) halos with a velocity dispersion s…
We have analyzed galaxy and group-sized dark matter halos formed in a high resolution LCDM numerical N-body simulation in order to study the rotation of the triaxial figure, a property in principle independent of the angular momentum of the particles themselves. Such figure rotation may have observational consequences, such as triggering spiral structure in extended gas disks. The orientation of the major axis is compared at 5 late snapshots of the simulation. Halos with significant substructure or that appear otherwise disturbed are excluded from the sample. We detect smooth figure rotation i…
In hierarchical models of structure formation, an early cosmic UV background (UVB) is produced by the small (T_vir < 10^4 K) halos that collapse before reionization. The UVB at energies below 13.6eV suppresses the formation of stars or black holes inside small halos, by photo-dissociating their only cooling agent, molecular H2. We self-consistently compute the buildup of the early UVB in Press-Schechter models, coupled with H2 photo-dissociation both in the intergalactic medium (IGM), and inside virialized halos. We find that the intergalactic H2 has a negligible effect on the UVB, both becaus…
Standard big bang nucleosynthesis predicts the average baryon density of the Universe to be a few percent of the critical density. Only about one tenth of the predicted baryons have been seen. A plausible respository for the missing baryons is in a diffuse ionized intergalactic medium (IGM). In an attempt to measure the IGM we searched for Thomson-scattered halos around strong high redshift radio sources. Observations of the radio source 1935-692 were made with the Australia Telescope Compact Array. We assumed a uniform IGM, and isotropic steady emission of 1935-692 for a duration between 10^7…
We combine the measurements of luminosity dependence of bias with the luminosity dependent weak lensing analysis of dark matter around galaxies to derive the galaxy bias and constrain nonlinear mass and cosmological parameters. We take advantage of theoretical and simulation predictions that predict that while halo bias is rapidly increasing with mass for high masses, it is nearly constant in low mass halos. We use a new weak lensing analysis around the same SDSS galaxies to determine their halo mass probability distribution. These halo mass probability distributions are used to predict the bi…
In this paper a series of high-resolution n-body simulations is presented in which the equations of motion have been changed to account for MOdified Newtonian Dynamics (MOND). It is shown that a low-Omega0 MONDian model with an appropriate choice for the normalisation sigma8 can lead to similar clustering properties at redshift z=0 as the commonly accepted (standard) LCDM model. However, such a model shows no significant structures at high redshift with only very few objects present beyond z>3 that can be readily ascribed to the low Omega0 value adopted. The agreement with LCDM at redshift z=0…
Models of disk galaxy formation commonly predict the existence of an extended reservoir of hot gas surrounding massive spirals at low redshift. As a test of these models, we have obtained X-ray and optical data of the two massive edge-on spirals NGC 5746 and NGC 5170, in order to investigate the amount and origin of hot gas in their disks and halos. Chandra observations of NGC 5746 reveal evidence for diffuse X-ray emission with a total luminosity of ~7 x 10^39 erg/s surrounding this galaxy out to at least ~20 kpc from the disk, whereas an identical study of the less massive NGC 5170 fails to …
We consider the ultra light pseudo Nambu-Goldstone boson appearing in the late time cosmological phase transition theories as a dark matter candidate. Since it is almost massless, its nature is more wave like than particle like. Hence we apply quantum mechanics to study how they form the galactic halos. Three predictions are made; (1)the mass profile $ρ\sim r^{-1.6}$, (2)there are ripple-like fine structures in rotation curve, (3) the rotation velocity times ripple's wave length is largely galaxy independent. We compare the rotation curves predicted by our theory with the data observed.
We present a comparison of halo properties in cosmological simulations of collisionless cold dark matter (CDM) and self-interacting dark matter (SIDM) for a range of dark matter cross sections. We find, in agreement with various authors, that CDM yields cuspy halos that are too centrally concentrated as compared to observations. Conversely, SIDM simulations using a Monte Carlo N-body technique produce halos with significantly reduced central densities and flatter cores with increasing cross section. We introduce a concentration parameter based on enclosed mass that we expect will be straightfo…
We present a kinetic theory for the evolution of the phase-space distribution of dark matter particles in galaxy halos in the presence of a cosmological spectrum of fluctuations. This theory introduces a new way to model the formation and evolution of halos, which traditionally have been investigated by analytic gravitational infall models or numerical N-body methods. Unlike the collisionless Boltzmann equation, our kinetic equation contains nonzero terms on the right-hand side arising from stochastic fluctuations in the gravitational potential due to substructures in the dark matter mass dist…
A complex scalar field has recently been suggested to bind galaxies and flatten the rotation curves of spirals. Its cosmological behavior is thoroughly investigated here. Such a field is shown to be a potential candidate for the cosmological dark matter that fills up a fraction Omega_cdm = 0.3 of the Universe. However, problems arise when the limits from galactic dynamics and some cosmological constraints are taken simultaneously into account. A free complex field, associated to a very small mass m = 10^{-23} eV, has a correct cosmological behavior in the early Universe, but behaves today most…
