8,206 research outputs found

    Stochastic Gravitational Wave Background originating from Halo Mergers

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    The stochastic gravitational wave background (GWB) from halo mergers is investigated by a quasi-analytic method. The method we employ consists of two steps. The first step is to construct a merger tree by using the Extended Press-Schechter formalism or the Sheth & Tormen formalism, with Monte-Carlo realizations. This merger tree provides evolution of halo masses. From NN-body simulation of two-halo mergers, we can estimate the amount of gravitational wave emission induced by the individual merger process. Therefore the second step is to combine this gravitaional wave emission to the merger tree and obtain the amplitude of GWB. We find ΩGW1019\Omega_{GW}\sim 10^{-19} for f10171016f\sim 10^{-17}-10^{-16} Hz, where ΩGW\Omega_{GW} is the energy density of the GWB. It turns out that most of the contribution on the GWB comes from halos with masses below 1015M10^{15} M_\odot and mergers at low redshift, i.e., 0<z<0.80<z<0.8.Comment: 5 pages, 8 figures. Accepted for publication in Physical Review

    Chemistry of aminoacylation of 5'-AMO and the origin of protein synthesis

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    Much of our recent work has been a study of aminoacyl AMP derivatives. Elucidation of the character of aminoacyl AMP derivatives has made it obvious that AMP has characteristics which should allow it to preferentially catalyze the synthesis of L-amino acid peptides. The essential features which lead to this conclusion are that all l-amino acids (but not all D amino acids) when esterified to 5'-AMP preferentially (65 percent) distribute to the 3' position of the 5'-AMP; that esterification is predominantly at the 2' position; that 2', 3' diaminoacyl esters are readily formed; and that a peptide bond can be formed between adjacent 2',3' aminoacyl esters

    Toward an Improved Analytical Description of Lagrangian Bias

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    We carry out a detailed numerical investigation of the spatial correlation function of the initial positions of cosmological dark matter halos. In this Lagrangian coordinate system, which is especially useful for analytic studies of cosmological feedback, we are able to construct cross-correlation functions of objects with varying masses and formation redshifts and compare them with a variety of analytical approaches. For the case in which both formation redshifts are equal, we find good agreement between our numerical results and the bivariate model of Scannapieco & Barkana (2002; SB02) at all masses, redshifts, and separations, while the model of Porciani et al. (1998) does well for all parameters except for objects with different masses at small separations. We find that the standard mapping between Lagrangian and Eulerian bias performs well for rare objects at all separations, but fails if the objects are highly-nonlinear (low-sigma) peaks. In the Lagrangian case in which the formation redshifts differ, the SB02 model does well for all separations and combinations of masses, apart from a discrepancy at small separations in situations in which the smaller object is formed earlier and the difference between redshifts or masses is large. As this same limitation arises in the standard approach to the single-point progenitor distribution developed by Lacey & Cole (1993), we conclude that a more complete understanding of the progenitor distribution is the most important outstanding issue in the analytic modeling of Lagrangian bias.Comment: 22 pages, 8 figures, ApJ, in pres

    Measuring the Cosmic Equation of State with Counts of Galaxies

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    The classical dN/dz test allows the determination of fundamental cosmological parameters from the evolution of the cosmic volume element. This test is applied by measuring the redshift distribution of a tracer whose evolution in number density is known. In the past, ordinary galaxies have been used as such a tracer; however, in the absence of a complete theory of galaxy formation, that method is fraught with difficulties. In this paper, we propose studying instead the evolution of the apparent abundance of dark matter halos as a function of their circular velocity, observable via the linewidths or rotation speeds of visible galaxies. Upcoming redshift surveys will allow the linewidth distribution of galaxies to be determined at both z~1 and the present day. In the course of studying this test, we have devised a rapid, improved semi-analytic method for calculating the circular velocity distribution of dark halos based upon the analytic mass function of Sheth et al. (1999) and the formation time distribution of Lacey & Cole (1993). We find that if selection effects are well-controlled and minimal external constraints are applied, the planned DEEP Redshift Survey should allow the measurement of the cosmic equation-of-state parameter w to 10% (as little as 3% if Omega_m has been well-determined from other observations). This type of test has the potential also to provide a constraint on any evolution of w such as that predicted by ``tracker'' models.Comment: 4 pages plus 3 embedded figures; version approved by Ap. J. Letters. A greatly improved error analysis has been added, along with a figure showing complementarity to other cosmological test

    Predictions from Star Formation in the Multiverse

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    We compute trivariate probability distributions in the landscape, scanning simultaneously over the cosmological constant, the primordial density contrast, and spatial curvature. We consider two different measures for regulating the divergences of eternal inflation, and three different models for observers. In one model, observers are assumed to arise in proportion to the entropy produced by stars; in the others, they arise at a fixed time (5 or 10 billion years) after star formation. The star formation rate, which underlies all our observer models, depends sensitively on the three scanning parameters. We employ a recently developed model of star formation in the multiverse, a considerable refinement over previous treatments of the astrophysical and cosmological properties of different pocket universes. For each combination of observer model and measure, we display all single and bivariate probability distributions, both with the remaining parameter(s) held fixed, and marginalized. Our results depend only weakly on the observer model but more strongly on the measure. Using the causal diamond measure, the observed parameter values (or bounds) lie within the central 2σ2\sigma of nearly all probability distributions we compute, and always within 3σ3\sigma. This success is encouraging and rather nontrivial, considering the large size and dimension of the parameter space. The causal patch measure gives similar results as long as curvature is negligible. If curvature dominates, the causal patch leads to a novel runaway: it prefers a negative value of the cosmological constant, with the smallest magnitude available in the landscape.Comment: 68 pages, 19 figure

    Effective Screening due to Minihalos During the Epoch of Reionization

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    We show that the gaseous halos of collapsed objects introduce a substantial cumulative opacity to ionizing radiation, even after the smoothly distributed hydrogen in the intergalactic medium has been fully reionized. This opacity causes a delay of around unity in redshift between the time of the overlap of ionized bubbles in the intergalactic medium and the lifting of complete Gunn-Peterson Lyman alpha absorption. The minihalos responsible for this screening effect are not resolved by existing numerical simulations of reionization.Comment: 24 pages, 5 figures, submitted to Ap

    Mass of Clusters in Simulations

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    We show that dark matter haloes, in n--body simulations, have a boundary layer (BL) with precise features. In particular, it encloses all dynamically stable mass while, outside it, dynamical stability is lost soon. Particles can pass through such BL, which however acts as a confinement barrier for dynamical properties. BL is set by evaluating kinetic and potential energies (T(r) and W(r)) and calculating R=-2T/W. Then, on BL, R has a minimum which closely approaches a maximum of w= -dlog W/dlog r. Such RwRw ``requirement'' is consistent with virial equilibrium, but implies further regularities. We test the presence of a BL around haloes in spatially flat CDM simulations, with or without cosmological constant. We find that the mass M_c, enclosed within the radius r_c, where the RwRw requirement is fulfilled, closely approaches the mass M_{dyn}, evaluated from the velocities of all particles within r_c, according to the virial theorem. Using r_c we can then determine an individual density contrast Delta_c for each virialized halo, which can be compared with the "virial" density contrast Δv 178Ωm0.45\Delta_v ~178 \Omega_m^{0.45} (Omega_m: matter density parameter) obtained assuming a spherically symmetric and unperturbed fluctuation growth. The spread in Delta_c is wide, and cannot be neglected when global physical quantities related to the clusters are calculated, while the average Delta_c is ~25 % smaller than the corresponding Delta_v; moreover if MdynM_{dyn} is defined from the radius linked to Delta_v, we have a much worse fit with particle mass then starting from {\it Rw} requirement.Comment: 4 pages, 5 figures, contribution to the XXXVIIth Rencontres de Moriond, The Cosmological Model, Les Arc March 16-23 2002, to appear in the proceeding

    Pointwise convergence of vector-valued Fourier series

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    We prove a vector-valued version of Carleson's theorem: Let Y=[X,H]_t be a complex interpolation space between a UMD space X and a Hilbert space H. For p\in(1,\infty) and f\in L^p(T;Y), the partial sums of the Fourier series of f converge to f pointwise almost everywhere. Apparently, all known examples of UMD spaces are of this intermediate form Y=[X,H]_t. In particular, we answer affirmatively a question of Rubio de Francia on the pointwise convergence of Fourier series of Schatten class valued functions.Comment: 26 page

    Formation time distribution of dark matter haloes: theories versus N-body simulations

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    This paper uses numerical simulations to test the formation time distribution of dark matter haloes predicted by the analytic excursion set approaches. The formation time distribution is closely linked to the conditional mass function and this test is therefore an indirect probe of this distribution. The excursion set models tested are the extended Press-Schechter (EPS) model, the ellipsoidal collapse (EC) model, and the non-spherical collapse boundary (NCB) model. Three sets of simulations (6 realizations) have been used to investigate the halo formation time distribution for halo masses ranging from dwarf-galaxy like haloes (M=103MM=10^{-3} M_*, where MM_* is the characteristic non-linear mass scale) to massive haloes of M=8.7MM=8.7 M_*. None of the models can match the simulation results at both high and low redshift. In particular, dark matter haloes formed generally earlier in our simulations than predicted by the EPS model. This discrepancy might help explain why semi-analytic models of galaxy formation, based on EPS merger trees, under-predict the number of high redshift galaxies compared with recent observations.Comment: 7 pages, 5 figures, accepted for publication in MNRA

    Dark-Halo Cusp: Asymptotic Convergence

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    We propose a model for how the buildup of dark halos by merging satellites produces a characteristic inner cusp, of a density profile \rho \prop r^-a with a -> a_as > 1, as seen in cosmological N-body simulations of hierarchical clustering scenarios. Dekel, Devor & Hetzroni (2003) argue that a flat core of a<1 exerts tidal compression which prevents local deposit of satellite material; the satellite sinks intact into the halo center thus causing a rapid steepening to a>1. Using merger N-body simulations, we learn that this cusp is stable under a sequence of mergers, and derive a practical tidal mass-transfer recipe in regions where the local slope of the halo profile is a>1. According to this recipe, the ratio of mean densities of halo and initial satellite within the tidal radius equals a given function psi(a), which is significantly smaller than unity (compared to being 1 according to crude resonance criteria) and is a decreasing function of a. This decrease makes the tidal mass transfer relatively more efficient at larger a, which means steepening when a is small and flattening when a is large, thus causing converges to a stable solution. Given this mass-transfer recipe, linear perturbation analysis, supported by toy simulations, shows that a sequence of cosmological mergers with homologous satellites slowly leads to a fixed-point cusp with an asymptotic slope a_as>1. The slope depends only weakly on the fluctuation power spectrum, in agreement with cosmological simulations. During a long interim period the profile has an NFW-like shape, with a cusp of 1<a<a_as. Thus, a cusp is enforced if enough compact satellite remnants make it intact into the inner halo. In order to maintain a flat core, satellites must be disrupted outside the core, possibly as a result of a modest puffing up due to baryonic feedback.Comment: 37 pages, Latex, aastex.cls, revised, ApJ, 588, in pres
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