17089668
ON THE REDSHIFT EVOLUTION OF Mg II ABSOPRTION SYSTEMS
We use a halo occupation approach to connect Mg II absorbers to dark matter halos as a function of redshift. Using the model constructed in Tinker & Chen, we parameterize the conditional probability of an absorber of equivalent width Wr being produced by a halo of mass Mh at a given redshift, P(Wr |Mh , z). We constrain the free parameters of the model by matching the observed statistics of Mg II absorbers: the frequency function f(Wr ), the redshift evolution n(z), and the clustering bias bW . The redshift evolution of Wr ≥ 1 A absorbers increases from z = 0.4 to z = 2, while the total halo cross section decreases monotonically with redshift. This discrepancy can only be explained if the gaseous halos evolve with respect to their host halos. We make predictions for the clustering bias of absorbers as a function of redshift under different evolutionary scenarios, e.g., the gas cross section per halo evolves or the halo mass scale of absorbers changes. We demonstrate that the relative contribution of these scenarios may be constrained by measurements of absorber clustering at z 1 and z ~ 0.1. If we further assume a redshift-independent mass scale for efficient shock heating of halo gas of M crit = 1011.5 h –1 M ☉, absorber evolution is predominantly caused by a changing halo mass scale of absorbers. Our model predicts that strong absorbers always arise in ~M crit halos, independent of redshift, but the mass scale of weak absorbers decreases by 2 dex from 0 < z < 2. Thus, the measured anti-correlation of clustering bias and Wr should flatten by z ~ 1.5.
119437353
Cosmic Voids and Galaxy Bias in the Halo Occupation Framework
We investigate the power of void statistics to constrain galaxy bias and the amplitude of dark matter fluctuations. We adopt a ΛCDM cosmological scenario (inflationary cold dark matter with a cosmological constant) and use the halo occupation distribution (HOD) framework to describe the relation between galaxies and dark matter. After choosing HOD parameters that reproduce the mean space density g and projected correlation function wp(rp) measured for galaxy samples with Mr < -19 and -21 from the Sloan Digital Sky Survey (SDSS), we predict the void probability function (VPF) and underdensity probability function (UPF) of these samples by populating the halos of a large, high-resolution N-body simulation (400 h-1 Mpc, 12803 particles). If we make the conventional simplifying assumption that the HOD is independent of large-scale environment at fixed halo mass, then models constrained to match g and wp(rp) predict nearly identical void statistics, independent of the scatter between halo mass and central galaxy luminosity or statistical uncertainties in HOD parameters. Models with power spectrum normalizations σ8 = 0.7 and 0.9 also predict very similar void statistics, with stronger galaxy bias compensating for weaker dark matter fluctuations in the low-σ8 model. However, the VPF and UPF are sensitive to environmental variations of the HOD in a regime where these variations have little impact on wp(rp). For example, doubling the minimum host halo mass in regions with large-scale (5 h-1 Mpc) density contrast δ < -0.65 has a readily detectable impact on void probabilities of Mr < -19 galaxies, and a similar change for δ < -0.2 alters the void probabilities of Mr < -21 galaxies at a detectable level. The VPF and UPF provide complementary information about the onset and magnitude of density dependence in the HOD. By detecting or ruling out HOD changes in low-density regions, void statistics can reduce systematic uncertainties in the cosmological constraints derived from HOD modeling and, more importantly, reveal connections between halo formation history and galaxy properties.
53557315
Galaxies in X-ray Groups II: A Weak Lensing Study of Halo Centering
Locating the centers of dark matter halos is critical for understanding the mass profiles of halos, as well as the formation and evolution of the massive galaxies that they host. The task is observationally challenging because we cannot observe halos directly, and tracers such as bright galaxies or X-ray emission from hot plasma are imperfect. In this paper, we quantify the consequences of miscentering on the weak lensing signal from a sample of 129 X-ray-selected galaxy groups in the COSMOS field with redshifts 0 < z < 1 and halo masses in the range 10{sup 13}-10{sup 14} M{sub Sun }. By measuring the stacked lensing signal around eight different candidate centers (such as the brightest member galaxy, the mean position of all member galaxies, or the X-ray centroid), we determine which candidates best trace the center of mass in halos. In this sample of groups, we find that massive galaxies near the X-ray centroids trace the center of mass to {approx}< 75 kpc, while the X-ray position and centroids based on the mean position of member galaxies have larger offsets primarily due to the statistical uncertainties in their positions (typically {approx}50-150 kpc). Approximately 30% of groups in our sample havemore » ambiguous centers with multiple bright or massive galaxies, and some of these groups show disturbed mass profiles that are not well fit by standard models, suggesting that they are merging systems. We find that halo mass estimates from stacked weak lensing can be biased low by 5%-30% if inaccurate centers are used and the issue of miscentering is not addressed.« less
14384746
On The Halo Occupation of Dark Baryons
We introduce a new technique that adopts the halo occupation framework for understanding the origin of QSO absorption-line systems. Our initial study focuses specifically on Mg II absorbers. We construct a model of the gaseous content in which the absorption equivalent width Wr is determined by the the amount of cold gas, in the form of discrete clouds, along a sightline through a halo. The two quantities that we specify per halo in the model are (1) the mean absorption strength per unit surface mass density AW (M), and (2) the mean covering factorg(M) of the gaseous clouds. These parameters determine the conditional probability distribution of Wr as a function of halo mass, P(Wr|M). Two empirical measurements are applied to constrain the model: (i) the absorber frequency distribution function and (ii) t he Wr-dependent clustering amplitude. We find that the data demand a rapid transition in the gas content of halos at ∼ 10 11.5 h -1 M⊙, below which halos contain predominantly cold gas and beyond which gas becomes predominantly hot. In order to reproduce the observed overall strong clustering of the absorbers and the anti-cor relation between Wr and halo mass M, roughly 5% of gas in halos up to 10 14 h -1 M⊙ is required to be cold. The gas covering factor is near unity over a wide range of halo mass, supporting that Mg II systems probe an unbiased sample of typical galaxies. We discuss the implications of our study in the contexts of mass assembly of distant galaxies and the origin of QSO absorption line systems. Subject headings:Cosmology: theory — dark matter halos — quasars: absorption lines — galaxies: evolution
34339487
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological constraints from the full shape of the clustering wedges
We explore the cosmological implications of the clustering wedges, ξ⊥(s) and ξ∥(s), of the CMASS Data Release 9 sample of the Sloan Digital Sky Survey III (SDSS-III) Baryon Oscillation Spectroscopic Survey. These clustering wedges are defined by averaging the full two-dimensional correlation function, ξ(μ, s), over the ranges 0 < μ < 0.5 and 0.5 < μ < 1, respectively. These measurements allow us to constrain the parameter combinations DA(z)/rs(zd) = 9.03 ± 0.21 and cz/(rs(zd)H(z)) = 12.14 ± 0.43 at the mean redshift of the sample, z = 0.57. We combine the information from the clustering wedges with recent measurements of cosmic microwave background (CMB), baryon acoustic oscillations and Type Ia supernovae to obtain constraints on the cosmological parameters of the standard Λ cold dark matter (ΛCDM) model and a number of potential extensions. The information encoded in the clustering wedges is most useful when the dark energy equation of state is allowed to deviate from its standard ΛCDM value. The combination of all data sets shows no evidence of a deviation from a constant dark energy equation of state, in which case we find wDE = −1.013 ± 0.064, in complete agreement with a cosmological constant. We explore potential deviations from general relativity (GR) by constraining the growth rate f(z) = d ln D(a)/d ln a, in which case the combination of the CMASS clustering wedges with CMB data implies f(z = 0.57) = 0.719−0.096+0.092, in accordance with the predictions of GR. Our results clearly illustrate the additional constraining power of anisotropic clustering measurements with respect to that of angle-averaged quantities.
55518354
New constraints on the evolution of the stellar-to-dark matter connection: a combined analysis of galaxy-galaxy lensing, clustering, and stellar mass functions from z=0.2 to z=1
Using data from the COSMOS survey, we perform the first joint analysis of galaxy-galaxy weak lensing, galaxy spatial clustering, and galaxy number densities. Carefully accounting for sample variance and for scatter between stellar and halo mass, we model all three observables simultaneously using a novel and self-consistent theoretical framework. Our results provide strong constraints on the shape and redshift evolution of the stellar-to-halo mass relation (SHMR) from z = 0.2 to z = 1. At low stellar mass, we find that halo mass scales as M-h proportional to M-*(0.46) and that this scaling does not evolve significantly with redshift from z = 0.2 to z = 1. The slope of the SHMR rises sharply at M-* \textgreater 5 x 10(10)M(circle dot) and as a consequence, the stellar mass of a central galaxy becomes a poor tracer of its parent halo mass. We show that the dark-to-stellar ratio, Mh/M*, varies from low to high masses, reaching a minimum of Mh/M-* similar to 27 at M-* = 4.5 x 10(10) M-circle dot and M-h = 1.2 x 10(12) M-circle dot. This minimum is important for models of galaxy formation because it marks the mass at which the accumulated stellar growth of the central galaxy has been themost efficient. We describe the SHMR at this minimum in terms of the “ pivot stellarmass,” M-*(piv) the “pivot halo mass,” M-h(piv), and the “pivot ratio,” (M-h/M-*)(piv). Thanks to a homogeneous analysis of a single data set spanning a large redshift range, we report the first detection of mass downsizing trends for both M-h(piv) and M-*(piv) The pivot stellar mass decreases from M-*(piv) = 5.75 +/- 0.13x10(10) M-circle dot at z = 0.88 to M-*(piv) = 3.55 +/- 0.17x10(10) M-circle dot at z = 0.37. Intriguingly, however, the corresponding evolution of M-h(piv) leaves the pivot ratio constant with redshift at (M-h/M-*)(piv) similar to 27. We use simple arguments to show how this result raises the possibility that star formation quenching may ultimately depend on M-h/M-* and not simply onMh, as is commonly assumed. We show that simple models with such a dependence naturally lead to downsizing in the sites of star formation. Finally, we discuss the implications of our results in the context of popular quenching models, including disk instabilities and active galactic nucleus feedback.
110270067
PRELIMINARY DESIGN OF FAST KICKER SYSTEM FOR BEPC II
With in BEPC II injection system there are two sets injection lines in storage ring each consisting of a pair of kicker magnets and one Lambertson magnet for e + and e injection respectively. The incoming beam is injected horizontally inside the storage ring. The linac provides the short pulsed bunch train of 3 micro bunches. There are six e + and six e -- bunch trains countermove in a same ring. The single bunch train injection is chosen. The duration of bunch train is 16ns. The kick of field is 130 Gauss-meter. The type of lumped ferrite inductance magnet with ceramic vacuum chamber is chosen. Per magnet consists of four modules each of 30 cm long, The field strength of magnet is 108 gauss. Excitation current is 631 A .The pulse field of magnet is a trapezoidal wave with duration less than 110ns, rise / fall time of K1 and fall / rise time of K2 is 33ns / 50ns respectively. The lumped LC network with impedance of 30ohm and voltage of 38kV is chosen as a pulser. The stray inductance of lead is controlled to be small enough by an air-insulated coaxial construction. Field rise time is reduced by the compensating capacitance and the fall time is reduced by second switch and saturable reactor. A ZVS PWM type of high voltage power supply is chosen as the charger for PFN. The details are described in this paper.
119272530
Model analysis of thermal UV-cutoff effects on the chiral critical surface at finite temperature and chemical potential
We study the effects of temporal UV-cutoff on the chiral critical surface in hot and dense QCD using a chiral effective model. Recent lattice QCD simulations indicate that the curvature of the critical surface might change toward the direction in which the first-order phase transition becomes stronger on increasing the number of lattice sites. To investigate this effect on the critical surface in an effective model approach, we use the Nambu-Jona-Lasinio model with finite Matsubara frequency summation. We find that the nature of the curvature of the critical surface does not alter appreciably as we decrease the summation number, which is unlike the case that was observed in recent lattice QCD studies. This may suggest that the dependence of chemical potential on the coupling strength or some additional interacting terms such as vector interactions could play an important role at finite density.
118416435
Shear viscosity of a gluon plasma in perturbative QCD
Abstract We calculate the shear viscosity ( η ) to entropy density ( s ) ratio η / s of a gluon plasma in kinetic theory including the g g → g g and g g → g g g processes. Due to the suppressed contribution to η in the g g → g g forward scattering, it is known that the gluon bremsstrahlung g g ↔ g g g process also contributes at the same order ( O ( α s − 2 ) ) in perturbative QCD. Using the Gunion–Bertsch formula for the g g → g g g matrix element which is valid for the limit of soft bremsstrahlung, we find that the result is sensitive to whether the same limit is taken for the phase space. Using the exact phase space, the g g ↔ g g g contribution becomes more important to η than g g → g g for α s ≳ 2 × 10 − 3 . Therefore, at α s = 0.1 , η / s ≃ 1.0 , between 2.7 obtained by Arnold, Moore and Yaffe (AMY) and 0.5 obtained by Xu and Greiner (XG). If the soft bremsstrahlung limit is imposed on the phase space such that the recoil effect from the bremsstrahlung gluon is neglected, then the correction from the g g ↔ g g g process is about 10–30% of the total which is close to AMY's prediction. This shows that further studies beyond the soft bremsstrahlung approximation used by XG and collinear approximation used by AMY are needed.
119355216
Spectral function of rho in dense and hot hadronic matter
The spectral function of rho meson in hot/dense hadronic matter is studied by taking into account the nucleon-loop on quantum hadrondynamics model level. Different from the hot pion gas effect which changes the spectral function slightly, the nucleon-antinucleon polarization (Dirac sea) makes the spectral function very sharp and shifted towards the low invariant mass region significantly due to the decreasing effective nucleon mass.
121696064
EFFECTIVE FIELD THEORY IN NUCLEAR ASTROPHYSICS
In this talk I review some general ideas of effective field theory and give examples of high precision calculations which have astrophysical applications. The examples are np→dγ for big-bang nucleosynthesis and νd inelastic scattering relevant for the solar neutrino detection processes employed by the Sudbury Neutrino Observatory.