# Browsing by Subject "large-scale structure"

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Item Ancient Light From Young Cosmic Cities: Physical And Observational Signatures Of Galaxy Proto-Clusters(2013-12) Chiang, Yi-Kuan; Overzier, Roderik; Gebhardt, Karl; Chiang, Yi-Kuan; Overzier, Roderik; Gebhardt, KarlShow more A growing number of galaxy clusters at z = 1-2 is being discovered as part of deep optical, IR, X-ray, and Sunyaev-Zel'dovich effect surveys. For a complete picture of cluster formation, however, it is important that we also start probing the much earlier epoch, between redshifts of about 2 and 7, during which these clusters and their galaxies first began to form. Because the study of these so-called proto-clusters is currently quite limited by small number statistics, widely varying selection techniques, and many assumptions, we have performed a large systematic study of cluster formation utilizing cosmological simulations. We use the Millennium Simulations to track the evolution of dark matter and galaxies in about 3000 clusters from the earliest times to z = 0. We define an effective radius R-e for proto-clusters and characterize their growth in size and mass with cosmic time. We show that the progenitor regions of galaxy clusters (ranging in mass from similar to 10(14) to a few times 10(15) M-circle dot) can already be identified in galaxy surveys at very early times (at least up to z similar to 5), provided that the galaxy overdensities are measured on a sufficiently large scale (R-e similar to 5-10 Mpc comoving) and with sufficient statistics. We present the overdensities in matter, dark matter halos, and galaxies as functions of present-day cluster mass, redshift, bias, and window size that can be used to interpret the wide range of structures found in real surveys. We also derive the probability that a structure having a galaxy overdensity delta(gal), defined by a set of observational selection criteria, is indeed a proto-cluster, and we show how their z = 0 masses can already be estimated long before virialization. We present overdensity profiles as a function of radius, and we further show how the projected surface overdensities of proto-clusters decrease as the uncertainties in redshift measurements increase. We provide a table of proto-cluster candidates selected from the literature and discuss their properties in light of our simulation predictions. This paper provides the general framework that will allow us to extend the study of cluster formation out to much higher redshifts using the large number of proto-clusters that are expected to be discovered in, e. g., the upcoming HETDEX and Hyper Suprime-Cam surveys.Show more Item Bullet Cluster: A Challenge To Lambda CDM Cosmology(2010-07) Lee, Jounghun; Komatsu, Eiichiro; Komatsu, EiichiroShow more To quantify how rare the bullet-cluster-like high-velocity merging systems are in the standard Lambda cold dark matter (CDM) cosmology, we use a large-volume (27 h(-3) Gpc(3)) cosmological N-body MICE simulation to calculate the distribution of infall velocities of subclusters around massive main clusters. The infall velocity distribution is given at (1-3) R(200) of the main cluster (where R(200) is similar to the virial radius), and thus it gives the distribution of realistic initial velocities of subclusters just before collision. These velocities can be compared with the initial velocities used by the non-cosmological hydrodynamical simulations of 1E0657-56 in the literature. The latest parameter search carried out by Mastropietro & Burkert has shown that an initial velocity of 3000 km s(-1) at about 2R(200) is required to explain the observed shock velocity, X-ray brightness ratio of the main and subcluster, X-ray morphology of the main cluster, and displacement of the X-ray peaks from the mass peaks. We show that such a high infall velocity at 2R(200) is incompatible with the prediction of a Lambda CDM model: the probability of finding 3000 km s(-1) in (2-3) R(200) is between 3.3 x 10(-11) and 3.6 x 10(-9). A lower velocity, 2000 km s(-1) at 2R(200), is also rare, and moreover, Mastropietro & Burkert have shown that such a low initial velocity does not reproduce the X-ray brightness ratio of the main and subcluster or morphology of the main cluster. Therefore, we conclude that the existence of 1E0657-56 is incompatible with the prediction of a Lambda CDM model, unless a lower infall velocity solution for 1E0657-56 with less than or similar to 1800 km s(-1) at 2R(200) is found.Show more Item Cluster Merger Shock Constraints On Particle Acceleration And Nonthermal Pressure In The Intracluster Medium(2008-03) Nakar, Ehud; Milosavljevic, Milos; Nagai, Daisuke; Milosavljevic, MilosShow more X-ray observations of galaxy cluster merger shocks can be used to constrain nonthermal processes in the intracluster medium (ICM). The presence of nonthermal pressure components in the ICM, as well as the shock acceleration of particles and their escape, all affect shock jump conditions in distinct ways. Therefore, these processes can be constrained using X-ray surface brightness and temperature maps of merger shock fronts. Here we use these observations to place constraints on particle acceleration efficiency in intermediate Mach number ( M approximate to 2-3) shocks and explore the potential to constrain the contribution of nonthermal components ( e. g., cosmic rays, magnetic field, and turbulence) to ICM pressure in cluster outskirts. We model the hydrodynamic jump conditions in merger shocks discovered in the galaxy clusters A520 ( M approximate to 2) and 1E 0657-56 ( M approximate to 3) using a multifluid model comprising a thermal plasma, a nonthermal plasma, and a magnetic field. Based on the published X-ray spectroscopic data alone, we find that the fractional contribution of cosmic rays accelerated in these shocks is less than or similar to 10% of the shock downstream pressure. Current observations do not constrain the fractional contribution of nonthermal components to the pressure of the undisturbed shock upstream. Future X-ray observations, however, have the potential to either detect particle acceleration in these shocks through its effect on the shock dynamics, or place a lower limit on the nonthermal pressure contributions in the undisturbed ICM. We briefly discuss implications formodels of particle acceleration in collisionless shocks and the estimates of galaxy cluster masses derived from X-ray and Sunyaev-Zel'dovich effect observations.Show more Item Cosmic Microwave Background-Weak Lensing Correlation: Analytical and Numerical Study of Nonlinearity and Implications for Dark Energy(2008-04) Nishizawa, Atushi J.; Komatsu, Eiichiro; Yoshida, Naoki; Takahashi, Ryuichi; Sugiyama, Naoshi; Komatsu, EiichiroShow more Evolution of density fluctuations yields secondary anisotropies in the cosmic microwave background ( CMB), which are correlated with the same density fluctuations that can be measured by weak lensing (WL) surveys. We study the CMB-WL correlation induced by the integrated Sachs-Wolfe (ISW) effect and its nonlinear extension, the Rees-Sciama (RS) effect, using analytical models as well as N-body simulations. We show that an analytical model based on the time derivative of matter power spectrum agrees with simulations. All-sky cosmic-variance-limited CMB and WL surveys allow us to measure the correlation from the nonlinear RS effect with high significance (50 sigma) for l(max) = 10(4) whereas forthcoming missions such as Planck and LSST are expected to yield 4 l p 10 1.5 sigma detections, on the assumption of that the point-source contributions are negligible. We find that the CMB-WL correlation has a characteristic scale which is sensitive to the nature of dark energy.Show more Item The Effect Of Environment On Shear In Strong Gravitational Lenses(2011-01) Wong, Kenneth C.; Keeton, Charles R.; Williams, Kurtis A.; Momcheva, Ivelina G.; Zabludoff, Ann I.; Williams, Kurtis A.Show more Using new photometric and spectroscopic data in the fields of nine strong gravitational lenses that lie in galaxy groups, we analyze the effects of both the local group environment and line-of-sight (LOS) galaxies on the lens potential. We use Monte Carlo simulations to derive the shear directly from measurements of the complex lens environment, providing the first detailed independent check of the shear obtained from lens modeling. We account for possible tidal stripping of the group galaxies by varying the fraction of total mass apportioned between the group dark matter halo and individual group galaxies. The environment produces an average shear of gamma = 0.08 (ranging from 0.02 to 0.17), significant enough to affect quantities derived from lens observables. However, the direction and magnitude of the shears do not match those obtained from lens modeling in three of the six four-image systems in our sample (B1422, RXJ1131, and WFI2033). The source of this disagreement is not clear, implying that the assumptions inherent in both the environment and lens model approaches must be reconsidered. If only the local group environment of the lens is included, the average shear is gamma = 0.05 (ranging from 0.01 to 0.14), indicating that LOS contributions to the lens potential are not negligible. We isolate the effects of various theoretical and observational uncertainties on our results. Of those uncertainties, the scatter in the Faber-Jackson relation and error in the group centroid position dominate. Future surveys of lens environments should prioritize spectroscopic sampling of both the local lens environment and objects along the LOS, particularly those bright (I < 21.5) galaxies projected within 5' of the lens.Show more Item Five-Year Wilkinson Microwave Anisotropy Probe Observations: Cosmological interpretation(2009-02) Komatsu, Eiichiro; Dunkley, J.; Nolta, M. R.; Bennett, C. L.; Gold, B.; Hinshaw, G.; Jarosik, N.; Larson, D.; Limon, M.; Page, L.; Spergel, D. N.; Halpern, M.; Hill, R. S.; Kogut, A.; Meyer, S. S.; Tucker, G. S.; Weiland, J. L.; Wollack, E.; Wright, E. L.; Komatsu, EiichiroShow more The Wilkinson Microwave Anisotropy Probe (WMAP) 5-year data provide stringent limits on deviations from the minimal, six-parameter. cold dark matter model. We report these limits and use them to constrain the physics of cosmic inflation via Gaussianity, adiabaticity, the power spectrum of primordial fluctuations, gravitational waves, and spatial curvature. We also constrain models of dark energy via its equation of state, parity-violating interaction, and neutrino properties, such as mass and the number of species. We detect no convincing deviations from the minimal model. The six parameters and the corresponding 68% uncertainties, derived from the WMAP data combined with the distance measurements from the Type Ia supernovae (SN) and the Baryon Acoustic Oscillations (BAO) in the distribution of galaxies, are: Omega(b)h(2) = 0.02267(-0.00059)(+0.00058), Omega(c)h(2) = 0.1131 +/- 0.0034, Omega(Lambda) = 0.726 +/- 0.015, n(s) = 0.960 +/- 0.013, tau = 0.084 +/- 0.016, and Delta(2)(R) = (2.445 +/- 0.096) x 10(-9) at k = 0.002 Mpc(-1). From these, we derive sigma(8) = 0.812 +/- 0.026, H-0 = 70.5 +/- 1.3 kms(-1) Mpc(-1), Omega(b) = 0.0456 +/- 0.0015, Omega(c) = 0.228 +/- 0.013, Omega(m)h(2) = 0.1358(-0.0036)(+0.0037), z(reion) = 10.9 +/- 1.4, and t(0) = 13.72 +/- 0.12 Gyr. With the WMAP data combined with BAO and SN, we find the limit on the tensor-to-scalar ratio of r < 0.22 (95% CL), and that n(s) > 1 is disfavored even when gravitational waves are included, which constrains the models of inflation that can produce significant gravitational waves, such as chaotic or power-law inflation models, or a blue spectrum, such as hybrid inflation models. We obtain tight, simultaneous limits on the (constant) equation of state of dark energy and the spatial curvature of the universe: -0.14 < 1 + w(0) < 0.12 (95% CL) and -0.0179 < Omega(k) < 0.0081 (95% CL). We provide a set of "WMAP distance priors," to test a variety of dark energy models with spatial curvature. We test a time-dependent w with a present value constrained as -0.33 < 1 + w(0) < 0.21 (95% CL). Temperature and dark matter fluctuations are found to obey the adiabatic relation to within 8.9% and 2.1% for the axion-type and curvaton-type dark matter, respectively. The power spectra of TB and EB correlations constrain a parity-violating interaction, which rotates the polarization angle and converts E to B. The polarization angle could not be rotated more than -5 degrees.9 < Delta alpha < 2 degrees.4 (95% CL) between the decoupling and the present epoch. We find the limit on the total mass of massive neutrinos of Sigma m(v) < 0.67 eV (95% CL), which is free from the uncertainty in the normalization of the large-scale structure data. The number of relativistic degrees of freedom (dof), expressed in units of the effective number of neutrino species, is constrained as N-eff = 4.4 +/- 1.5 (68%), consistent with the standard value of 3.04. Finally, quantitative limits on physically-motivated primordial non-Gaussianity parameters are -9 < f(NL)(local) < 111 (95% CL) and -151 < f(NL)(equil) < 253 (95% CL) for the local and equilateral models, respectively.Show more Item The Impact Of Cold Dark Matter Variants On The Halos Of The First Stars And Galaxies: Angular Momentum And Vortex Creation In BEC Dark Matter(2010-11) Rindler-Daller, T.; Shapiro, P. R.; Rindler‐Daller, Tanja; Shapiro, Paul R.Show more If cold dark matter elementary particles form a Bose-Einstein condensate, their superfluidity may distinguish them from other forms of cold dark matter, including the creation of quantum vortices. We have shown that such vortices are favored in strongly-coupled condensates. Vortex creation causes central densities to drop, thus affecting the dynamics of the gaseous baryonic component and subsequently star formation.Show more Item A Massive, Distant Proto-Cluster at Z=2.47 Caught in a Phase of Rapid Formation?(2015-08) Casey, C. M.; Cooray, A.; Capak, P.; Fu, H.; Kovac, K.; Lilly, S.; Sanders, D. B.; Scoville, N. Z.; Treister, E.; Casey, C. M.Show more Numerical simulations of cosmological structure Formation show that the universe's most massive clusters, and the galaxies living in those clusters, assemble rapidly at early times (2.5 < z < 4). While more than 20 proto-clusters have been observed at z greater than or similar to 2 based on associations of 5-40 galaxies around rare sources, the observational evidence for rapid cluster Formation is weak. Here we report observations of an asymmetric filamentary structure at z = 2.47 containing 7 starbursting, submillimeter-luminous galaxies and 5 additional active galactic nuclei (AGNs) within a comoving volume of 15,000 Mpc(3). As the expected lifetime of both the luminous AGN and starburst phase of a galaxy is similar to 100 Myr, we conclude that these sources were likely triggered in rapid succession by environmental factors or, alternatively, the duration of these cosmologically rare phenomena is much longer than prior direct measurements suggest. The stellar mass already built up in the structure is similar to 10(12) M-circle dot and we estimate that the cluster mass will exceed that of the Coma supercluster at z similar to 0. The filamentary structure is in line with hierarchical growth simulations that predict that the peak of cluster activity occurs rapidly at z > 2.Show more Item Perturbation Theory Reloaded. II. Nonlinear Bias, Baryon Acoustic Oscillations, And Millennium Simulation In Real Space(2009-01) Jeong, Donghui; Komatsu, Eiichiro; Jeong, Donghui; Komatsu, EiichiroShow more We calculate the nonlinear galaxy power spectrum in real space, including nonlinear distortion of the baryon acoustic oscillations, using the standard third-order perturbation theory (PT). The calculation is based upon the assumption that the number density of galaxies is a local function of the underlying, nonlinear density field. The galaxy bias is allowed to be both nonlinear and stochastic. We show that the PT calculation agrees with the galaxy power spectrum estimated from the Millennium Simulation, in the weakly nonlinear regime (defined by the matter power spectrum) at high redshifts, 1 <= z <= 6. We also show that, once three free parameters characterizing galaxy bias are marginalized over, the PT power spectrum fit to the Millennium Simulation data yields unbiased estimates of the distance scale, D, to within the statistical error. This distance scale corresponds to the angular diameter distance, D(A)(z), and the expansion rate, H(z), in real galaxy surveys. Our results presented in this paper are still restricted to real space. The future work should include the effects of nonlinear redshift space distortion. Nevertheless, our results indicate that nonlinear galaxy bias in the weakly nonlinear regime at high redshifts is reasonably under control.Show more Item Resolving The Optical Emission Lines Of Ly Alpha Blob "B1" At Z=2.38: Another Hidden Quasar(2013-07) Overzier, Roderik A.; Nesvadba, Nesvadba P. H.; Dijkstra, M.; Hatch, N. A.; Lehnert, M. D.; Villar-Martin, M.; Wilman, R. J.; Zirm, A. W.; Overzier, Roderik A.Show more We have used the SINFONI near-infrared integral field unit on the Very Large Telescope to resolve the optical emission line structure of one of the brightest (L-Ly alpha approximate to 10(44) erg s(-1)) and nearest (z approximate to 2.38) of all Ly alpha blobs (LABs). The target, known in the literature as object "B1", lies at a redshift where the main optical emission lines are accessible in the observed near-infrared. We detect luminous [OIII]lambda lambda 4959,5007 and H alpha emission with a spatial extent of at least 32 x 40 kpc (4 '' x 5 ''). The dominant optical emission line component shows relatively broad lines (600-800 km s(-1), FWHM) and line ratios consistent with active galactic nucleus (AGN) photoionization. The new evidence for AGN photoionization, combined with previously detected CIV and luminous, warm infrared emission, suggest that B1 is the site of a hidden quasar. This is confirmed by the fact that [OII] is relatively weak compared with [OIII] (extinction-corrected [OIII]/[OII] of about 3.8), which is indicative of a high, Seyfert-like ionization parameter. From the extinction-corrected [OIII] luminosity we infer a bolometric AGN luminosity of similar to 3x10(46) erg s(-1), and further conclude that the obscured AGN may be Compton-thick given existing X-ray limits. The large line widths observed are consistent with clouds moving within the narrow-line region of a luminous QSO. The AGN scenario is capable of producing sufficient ionizing photons to power the Ly alpha, even in the presence of dust. By performing a census of similar objects in the literature, we find that virtually all luminous LABs harbor obscured quasars. Based on simple duty-cycle arguments, we conclude that AGNs are the main drivers of the Ly alpha in LABs rather than the gravitational heating and subsequent cooling suggested by cold stream models. We also conclude that the empirical relation between LABs and overdense environments at high redshift must be due to a more fundamental correlation between AGNs (or massive galaxies) and environment.Show more Item A Second-Order Bias Model For The Logarithmic Halo Mass Density(2012-07) Jee, Inh; Park, Changbom; Kim, Juhan; Choi, Yun-Yong; Kim, Sungsoo S.; Jee, InhShow more We present an analytic model for the local bias of dark matter halos in a Lambda CDM universe. The model uses the halo mass density instead of the halo number density and is searched for various halo mass cuts, smoothing lengths, and redshift epochs. We find that, when the logarithmic density is used, the second-order polynomial can fit the numerical relation between the halo mass distribution and the underlying matter distribution extremely well. In this model, the logarithm of the dark matter density is expanded in terms of log halo mass density to the second order. The model remains excellent for all halo mass cuts (from M-cut = 3 x 10(11) to 3 x 10(12) h (1) M-circle dot), smoothing scales (from R = 5 h(-1) Mpc to 50h(-1) Mpc), and redshift ranges (from z = 0 to 1.0) considered in this study. The stochastic term in the relation is found to be not entirely random, but a part of the term can be determined by the magnitude of the shear tensor.Show more