In the previous parts of the discussion on the same topic, various aspects of the very early universe were discussed. We discussed how inclusion of large dark energy term compensates for the net gravity. Here the discussion is taken further including the effects of charge, magnetic fields and rotation. The role of large extra dimensions under the extreme initial conditions is discussed and possible connection with the cyclic brane theory is explored. We constrain various cosmic quantities like the net charge, number density of magnetic monopoles, primordial magnetic fields, size of the extra dimensions,etc.
Matter collapsing to a singularity in a gravitational field is still an intriguing question. Similar situation arises when discussing the very early universe or a universe recollapsing to a singularity. It is suggested that inclusion of mutual gravitational interactions among the collapsing particles can avert a singularity and give finite value for various physical quantities like entropy, density, etc.
In a recent paper it was suggested that inclusion of mutual gravitational interactions among the collapsing particles can avert a singularity and give finite value for various physical quantities. In this paper we extend this idea further by the inclusion of charge and spin to the system. We have also discussed other possible scenarios by which the singular state can be averted, including a temperature dependent gravitational constant. Also possible modifications in the Einstein-Hilbert action have been discussed, which can again lead to a finite maximal curvature hence avoiding a singularity.
We review some of the possible observable effects (reionization, feedback on galaxy formation, supernovae and metal enrichment) of the first collapsed, luminous (Pop III) objects in the universe. We show that supernovae in these objects should be considerably magnified by the intervening cosmological matter distribution; the implications of this process are briefly discussed, anticipating some of the results of Marri & Ferrara (1998).
In this paper the role of very massive pop III stars in the chemical enrichment of the early universe is discussed. We first compare our predictions with the abundance ratios measured in the high redshift Lyman-alpha forest to check whether they are compatible with the values predicted by assuming that the early universe was enriched by massive pop III stars. We conclude that to explain the observed C/Si ratio in the intergalactic medium, a contribution from pop II stars to carbon enrichment is necessary, already at redshift z=5. We then evaluate the number of Pair-Instability Supernovae (SN_(…
We study the effects of the ionizing and dissociating photons produced by Pop III objects on the surrounding intergalactic medium. We find that the typical size of a H_2 photodissociated region is smaller than the mean distance between sources at z=20-30, but larger than the ionized region. This implies that clearing of the intergalactic H_2 occurs before reionization of the universe is complete. In the same redshift range, the soft-UV background in the Lyman- Werner bands, when the intergalactic H and H_2 opacity is included, is found to be J_LW = 10^-28 - 10^-26 erg cm^-2 s^-1 Hz^-1. This va…
The WMAP satellite has measured a large optical depth to electron scattering after cosmological recombination of 0.17+-0.04, implying significant reionization of the primordial gas only ~200 million years after the big bang. However, the most recent overlap of intergalactic HII regions must have occured at z<9 based on the Lyman-alpha forest constraint on the thermal history of the intergalactic medium. Here we argue that a first generation of metal-free stars with a heavy (rather than Salpeter) mass function is therefore required to account for much of the inferred optical depth. This conclus…
(abridged) We perform 12 extremely high resolution adaptive mesh refinement cosmological hydrodynamic simulations of Population III star formation in a Lambda CDM universe, varying the box size and large-scale structure, to understand systematic effects in the formation of primordial protostellar cores. We find results that are qualitatively similar to those observed previously. We observe that the threshold halo mass for formation of a Population III protostar does not evolve significantly with time in the redshift range studied (33 > z > 19) but exhibits substantial scatter due to different …
Cyclical wind variability is an ubiquitous but as yet unexplained feature among OB stars. The O7.5 III(n)((f)) star xi Persei is the brightest representative of this class on the Northern hemisphere. As its prominent cyclical wind properties vary on a rotational time scale (2 or 4 days) the star has been already for a long time a serious magnetic candidate. As the cause of this enigmatic behavior non-radial pulsations and/or a surface magnetic field are suggested. We present a preliminary report on our attempts to detect a magnetic field in this star with high-resolution measurements obtained …
We note that current observational evidence strongly favors a conventional recombination of ionized matter subsequent to redshift z=1200, followed by reionization prior to redshift z=5 and compute how this would have occurred in a standard scenario for the growth of structure. Extending prior semi-analytic work, we show by direct, high-resolution numerical simulations (of a COBE normalized CDM+Lambda model) that reheating, will occur in the interval 15>z>7, followed by reionization and accompanied by a significant increase in the Jeans mass. However, the evolution of the Jeans mass does not si…
We provide a new tool to interpret the large scale structure of the Universe. As suggested in Paper II, energy density filaments could have been produced by subjacent magnetic flux tubes when the Universe was dominated by radiation. In more recent time epochs, small scale filaments have evolved in a complicated way, but large scale filaments have probably survived and should be identified with present observed matter filaments of clusters. A primordial magnetic field lattice made up of magnetic flux tubes would then have originated a matter lattice made up of cluster filaments. Taking into acc…
The first metal enrichment in the universe was made by supernova (SN) explosions of population (Pop) III stars. The trace remains in abundance patterns of extremely metal-poor (EMP) stars. We investigate the properties of nucleosynthesis in Pop III SNe by means of comparing their yields with the abundance patterns of the EMP stars. We focus on (1) jet-induced SNe with various energy deposition rates [$\dot{E}_{\rm dep}=(0.3-1500)\times10^{51}{\rm ergs s^{-1}}$], and (2) SNe of stars with various main-sequence masses ($M_{\rm ms}=13-50M_\odot$) and explosion energies [$E=(1-40)\times10^{51}$erg…
The character of the first galaxies at redshifts z > 10 strongly depends on their level of pre-enrichment, which is in turn determined by the rate of primordial star formation prior to their assembly. In order for the first galaxies to remain metal-free, star formation in minihaloes must be highly suppressed, most likely by H2-dissociating Lyman-Werner (LW) radiation. We show that the build-up of such a strong LW background is hindered by two effects. Firstly, the level of the LW background is self-regulated, being produced by the Population III (Pop III) star formation which it, in turn, supp…
We present a luminosity function for low surface brightness (LSB) galaxies identified in the APM survey of Impey et al 1996. These galaxies have central surface brightnesses in B in the range 22 < mu < 25. Using standard maximum-likelihood estimators, we determine that the best-fit Schechter function parameters for this luminosity function (LF) are alpha = -1.42, M* = -18.34, and phi* = 0.0036, assuming H_0 = 100. We compare these results to those of other recent studies and find that surveys which do not take account of the observation selection bias imposed by surface brightness are missing …
Using an analytical model, we compute the distribution of image separations resulting from gravitational lensing of distant sources, for 7 COBE-normalized CDM models with various combinations of Omega_0 and lambda_0. Our model assumes that multiple imaging results from strong lensing by individual galaxies. We model galaxies as nonsingular isothermal spheres, and take into account the finite angular size of the sources. Our model neglects the contribution of the background matter distribution, and assumes that lensing is entirely caused by galaxies. To test the validity of this assumption, we …
We construct star formation histories at redshifts z > 5 for two physically distinct populations of primordial, metal-free stars, motivated by theoretical and observational arguments that have hinted towards the existence of an intermediate stellar generation between Population III and Population I/II. Taking into account the cosmological parameters as recently revised by WMAP after three years of operation, we determine self-consistent reionization histories and discuss the resulting chemical enrichment from these early stellar generations. We find that the bulk of ionizing photons and heavy …
We calculate the global star formation rate density (SFRD) from z ~ 30-3 using a semi-analytic model incorporating the hierarchical assembly of dark matter halos, gas cooling via atomic hydrogen, star formation, supernova feedback, and suppression of gas collapse in small halos due to the presence of a photoionizing background. We compare the results with the predictions of simpler models based on the rate of dark matter halo growth and a fixed ratio of stellar-to-dark mass, and with observational constraints on the SFRD at 3 < z < 6. We also estimate the star formation rate due to very massiv…
We examine aspects of primordial star formation in the presence of a molecular hydrogen-dissociating ultraviolet background. We compare a set of AMR hydrodynamic cosmological simulations using a single cosmological realization but with a range of ultraviolet background strengths in the Lyman-Werner band. This allows us to study the effects of Lyman-Werner radiation on suppressing H2 cooling at low densities as well as the high-density evolution of the collapsing core in a self-consistent cosmological framework. We find that the addition of a photodissociating background results in a delay of t…
The history of the transition from a neutral intergalactic medium (IGM) to one that is almost fully ionized can reveal the character of cosmological ionizing sources. We study the evolution of the volume filling factor of HII and HeIII regions in a clumpy IGM, and discuss the implications for rival reionization scenarios of the rapid decline in the space density of radio-loud quasars and of the large population of star-forming galaxies recently observed at z>3. The hydrogen component in a highly inhomogeneous universe is completely reionized when the number of photons emitted above 1 ryd in on…
Large inhomogeneities in neutral hydrogen in the universe can be detected at redshifts $z \leq 10$ using the redshifted 21 cm line emission. We use cosmological N-Body simulations for dark matter and a simple model for baryonic collapse to estimate the signal expected from structures like proto-clusters of galaxies at high redshifts. We study: (i) the standard CDM model, (ii) a modified CDM model with less power at small scales, and (iii) a $Λ+$CDM model in a universe with $Ω_0 + Ω_Λ= 1$. We show that it should be possible for the next generation radio telescopes to detect such structures at t…
We study the Einstein-Klein-Gordon equations for a convex positive potential in a Bianchi I, a Bianchi III and a Kantowski-Sachs universe. After analysing the inherent properties of the system of differential equations, the study of the asymptotic behaviors of the solutions and their stability is done for an exponential potential. The results are compared with those of Burd and Barrow. In contrast with their results, we show that for the BI case isotropy can be reached without inflation and we find new critical points which lead to new exact solutions. On the other hand we recover the result o…
I review various aspects of the role neutrinos have played in shaping various cosmological observables: the nature of large scale structure, observed fluctuations in the CMB, the nature of matter, and the shape of things to come. (Invited review lecture III International Workshop on NO-VE, Venice, 2006)
We investigate the formation of dust grains in the ejecta of population III supernovae including pair--instability supernovae, applying a theory of non-- steady state nucleation and grain growth. In the calculations, the time evolution of gas temperature in theejecta, which strongly affects the number density and size of newly formed grains, is calculated by solving the radiative transfer equation taking account of the energy deposition of radio active elements. Two extreme cases are considered for the mixing of elements in the ejecta; unmixed and uniformly mixed cases within the He--core. The…
In this paper we briefly review some of the most recent developments concerning the formation of the first luminous objects in the universe, to which we refer to as Pop III objects, and their observable effects. In particular, we try to critically discuss the possible connection between them and dwarf spheroidal galaxies. We come to the conclusion that, if the properties of Pop IIIs are correctly predicted by hierarchical cosmological models, their identification with present day dwarf galaxies presents several difficulties.
We present new results from the SCUBA Local Universe Galaxy Survey (SLUGS), the first large systematic submillimetre survey of the local Universe. Since our initial survey of a sample of 104 IRAS-selected galaxies we have now completed a survey of a sample of 81 optically-selected galaxies, observed with the SCUBA camera on the James Clerk Maxwell Telescope. Since SCUBA is sensitive to the 90% of dust too cold to radiate significantly in the IRAS bands our new sample represents the first unbiased survey of dust in galaxies along the whole length of the Hubble sequence. We find little change in…
We investigate the impact of an early population of massive stars on their surroundings. Dissociation of molecular hydrogen by strong UV emission from such stars is expected to produce a global transition in the cooling mechanism of minihalos at a redshift of approximately 30, strongly inhibiting star formation until more massive halos can collapse. Furthermore, chemical enrichment from Pop III supernovae produces a second transition at z ~ 15-20, when the mean metallicity of the universe exceeds a critical threshold and Pop III star formation gives way to Pop II. We show that observations of …
We show the universe was reionized twice, first at z~15-16 and second at z~6. Such an outcome appears inevitable, when normalizing to two well determined observational measurements, namely, the epoch of the final cosmological reionization at z~6 and the density fluctuations at z~6, which in turn are tight ly constrained by Lyman alpha forest observations at z~3. These two observations most importantly fix the product of star formation efficiency and ionizing photon escape fraction from galaxies at high redshift. To the extent that the relative star formation efficiencies in gaseous minihalos w…
By correcting the redshift--dependent distances for peculiar motions through a number of peculiar velocity field models, we recover the true distances of a wide, all-sky sample of nearby galaxies (~ 6400 galaxies with velocities cz<5500 km/s), which is complete up to the blue magnitude B=14 mag. Relying on catalogs of galaxy groups, we treat ~2700 objects as members of galaxy groups and the remaining objects as field galaxies. We model the peculiar velocity field using: i) a cluster dipole reconstruction scheme; ii) a multi--attractor model fitted to the Mark II and Mark III catalogs of galaxy…
In this paper we examine aspects of primordial star formation in a gravitino warm dark matter universe with a cosmological constant. We compare a set of simulations using a single cosmological realization but with a wide range of warm dark matter particle masses which have not yet been conclusively ruled out by observations. The addition of a warm dark matter component to the initial power spectrum results in a delay in the collapse of high density gas at the center of the most massive halo in the simulation and, as a result, an increase in the virial mass of this halo at the onset of baryon c…
We present recent progress in searching for galaxies at redshift from z = 5 to z = 10. Wide-field and senstive surveys with 8m class telescopes have been providing more than several hundreds of star forming galaxies at z =5 - 7 that are probed in the optical window. These galaxies are used to study the early cosmic star formation activity as well as the early structure formation in the universe. Moreover, near infrared deep imaging and spectropscopic surveys have found probable candidates of galaxies from z = 7 to z = 10. Although these candidates are too faint to be identified unambiguously, …
We examine in detail the dynamical structure of an elliptical galaxy simulated in the Lambda CDM scenario. The morphology of the galaxy evolves dramatically over time in response to the mode and timing of mass accretion; smooth deposition of cooled gas leads to the formation of centrifugally supported disks, whilst major mergers disperse stellar disks into spheroids. These two modes of accretion alternate successively until z~0.6, when the galaxy undergoes one last major (1:2) merger that consumes much of the remaining gas into stars. Little gas cools and accretes subsequently and, as a result…
This is the third paper in a series which combines N-body simulations and semi-analytic modelling to provide a fully spatially resolved simulation of the galaxy formation and clustering processes. Here we extract mock redshift surveys from our simulations: a Cold Dark Matter model with either Omega_0=1 (tauCDM) or Omega_0=0.3 and Lambda=0.7 (LambdaCDM). We compare the mock catalogues with the northern region (CfA2N) of the Center for Astrophysics (CfA) Redshift Surveys. We study the properties of galaxy groups and clusters identified using standard observational techniques and we study the rel…
This paper is the third of a series dedicated to the study of the Delayed Big-Bang (DBB) class of inhomogeneous cosmological models of Lemaître-Tolman-Bondi type. In the first work, it was shown that the geometrical properties of the DBB model are such that the horizon problem can be solved, without need for any inflationary phase, for an observer situated sufficiently near the symmetry center of the model to justify the ``centered earth'' approximation. In the second work, we studied, in a peculiar subclass of the DBB models, the extent to which the values of the dipole and quadrupole moments…
