Browsing by Subject "large-scale structure of universe"

Now showing 1 - 13 of 13

Bullet Cluster: A Challenge To Lambda CDM Cosmology
(2010-07) Lee, Jounghun; Komatsu, Eiichiro; Komatsu, Eiichiro
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.
Effects Of Large-Scale Environment On The Assembly History Of Central Galaxies
(2014-10) Jung, Intae; Lee, Jaehyun; Yi, Sukyoung K.; Jung, Intae
We examine whether large-scale environment affects the mass assembly history of central galaxies. To facilitate this, we constructed dark matter halo merger trees from a cosmological N-body simulation and calculated the formation and evolution of galaxies using a semi-analytic method. We confirm earlier results that smaller halos show a notable difference in formation time with a mild dependence on large-scale environment. However, using a semi-analytic model, we found that on average the growth rate of the stellar mass of central galaxies is largely insensitive to large-scale environment. Although our results show that the star formation rate (SFR) and the stellar mass of central galaxies in smaller halos are slightly affected by the assembly bias of halos, those galaxies are faint and the difference in the SFR is minute, therefore it is challenging to detect it in real galaxies given the current observational accuracy. Future galaxy surveys, such as the BigBOSS experiment and the Large Synoptic Survey Telescope, which are expected to provide observational data for fainter objects, will provide a chance to test our model predictions.
Extracting Angular Diameter Distance And Expansion Rate Of The Universe From Two-Dimensional Galaxy Power Spectrum At High Redshifts: Baryon Acoustic Oscillation Fitting Versus Full Modeling
(2009-03) Shoji, Masatoshi; Jeong, Donghui; Komatsu, Eiichiro; Shoji, Masatoshi; Jeong, Donghui; Komatsu, Eiichiro
We present a method for extracting the angular diameter distances, D(A), and the expansion rates, H, of the universe from the two-dimensional baryon acoustic oscillations (BAO) in the galaxy power spectrum. Our method builds upon the existing algorithm called the "fit-and-extract" (FITEX) method, which allows one to extract only D(A)(2)/H from a spherically averaged one-dimensional power spectrum. We develop the FITEX-2d method, an extension of the FITEX method, to include the two-dimensional information, which allows us to extract D(A) and H simultaneously. We test the FITEX-2d method using the Millennium Simulation as well as simplified Monte Carlo simulations with a bigger volume. The BAOs, however, contain only a limited amount of information. We show that the full modeling, including the overall shape of the power spectrum, yields much better determinations of D(A) and H, hence the dark energy equation of Stateparameters such as w(0) and w(a), than the BAO-only analysis by more than a factor of 2, provided that nonlinear effects are under control.
Five-Year Wilkinson Microwave Anisotropy Probe Observations: Angular Power Spectra
(2009-02) Nolta, M. R.; Dunkley, J.; Hill, R. S.; Hinshaw, G.; Komatsu, Eiichiro; Larson, D.; Page, L.; Spergel, D. N.; Bennett, C. L.; Gold, B.; Jarosik, N.; Odegard, N.; Weiland, J. L.; Wollack, E.; Halpern, M.; Kogut, A.; Limon, M.; Meyer, S. S.; Tucker, G. S.; Wright, E. L.; Komatsu, Eiichiro
We present the temperature and polarization angular power spectra of the cosmic microwave background derived from the first five years of Wilkinson Microwave Anisotropy Probe data. The five-year temperature spectrum is cosmic variance limited up to multipole l = 530, and individual l-modes have signal-to-noise ratio S/N > 1 for l < 920. The best-fitting six-parameter Lambda CDM model has a reduced chi(2) for l = 33-1000 of chi(2)/nu = 1.06, with a probability to exceed of 9.3%. There is now significantly improved data near the third peak which leads to improved cosmological constraints. The temperature-polarization correlation is seen with high significance. After accounting for foreground emission, the low-l reionization feature in the EE power spectrum is preferred by Delta chi(2) = 19.6 for optical depth tau = 0.089 by the EE data alone, and is now largely cosmic variance limited for l = 2-6. There is no evidence for cosmic signal in the BB, TB, or EB spectra after accounting for foreground emission. We find that, when averaged over l = 2-6, l(l + 1)CBB(l)(BB)/(2 pi) < 0.15 mu K(2) (95% CL).
The Herschel Stripe 82 Survey (HerS): Maps and Early Catalog
(2014-02) Viero, M. P.; Asboth, V.; Roseboom, I. G.; Moncelsi, L.; Marsden, G.; Cooper, E. Mentuch; Zemcov, M.; Addison, G.; Baker, A. J.; Beelen, A.; Bock, J.; Bridge, C.; Conley, A.; Devlin, M. J.; Dore, O.; Farrah, D.; Finkelstein, S.; Font-Ribera, A.; Geach, J. E.; Gebhardt, Karl; Gill, A.; Glenn, Jason; Hajian, A.; Halpern, M.; Jogee, S.; Kurczynski, P.; Lapi, A.; Negrello, M.; Oliver, S. J.; Papovich, C.; Quadri, R.; Ross, N.; Scott, D.; Schulz, B.; Somerville, R.; Spergel, D. N.; Vieira, J. D.; Wang, L.; Wechsler, R.; Cooper, E. Mentuch; Finkelstein, S.; Jogee, S.
We present the first set of maps and band-merged catalog from the Herschel Stripe 82 Survey (HerS). Observations at 250, 350, and 500 mu m were taken with the Spectral and Photometric Imaging Receiver instrument aboard the Herschel Space Observatory. HerS covers 79 deg(2) along the SDSS Stripe 82 to an average depth of 13.0, 12.9, and 14.8 mJy beam(-1) (including confusion) at 250, 350, and 500 mu m, respectively. HerS was designed to measure correlations with external tracers of the dark matter density field-either point-like (i.e., galaxies selected from radio to X-ray) or extended (i.e., clusters and gravitational lensing)-in order to measure the bias and redshift distribution of intensities of infrared-emitting dusty star-forming galaxies and active galactic nuclei. By locating HerS in Stripe 82, we maximize the overlap with available and upcoming cosmological surveys. The band-merged catalog contains 3.3 x 10(4) sources detected at a significance of >= 3 sigma (including confusion noise). The maps and catalog are available at http://www.astro.caltech.edu/hers/.
A Large-Scale Galaxy Structure At Z=2.02 Associated With The Radio Galaxy MRC 0156-252
(2013-11) Galametz, Audrey; Stern, Daniel; Pentericcil, Laura; De Breuck, Carlos; Vernet, Joël; Wylezalek, Dominika; Fassbender, Rene; Hatch, Nina; Kurk, Jaron; Overzier, Roderik; Rettura, Alessandro; Seymour, Nick; Overzier, Roderik
We present the spectroscopic confirmation of a structure of galaxies surrounding the radio galaxy MRC 0156-252 at z = 2.02. The structure was initially discovered as an overdensity of both near-infrared selected z > 1.6 and mid-infrared selected z > 1.2 galaxy candidates. We used the VLT/FORS2 multi-object spectrograph to target similar to 80 high-redshift galaxy candidates, and obtain robust spectroscopic redshifts for more than half the targets. The majority of the confirmed sources are star-forming galaxies at z > 1.5. In addition to the radio galaxy, two of its close-by companions (<6 '') also show AGN signatures. Ten sources, including the radio galaxy, lie within vertical bar z - 2.020 vertical bar < 0.015 (i.e., velocity offsets < 1500 km s(-1)) and within projected 2 Mpc comoving of the radio galaxy. Additional evidence suggests not only that the galaxy structure associated with MRC 0156-252 is a forming galaxy cluster but also that this structure is most probably embedded in a larger-scale structure.
Ly Alpha-Emitting Galaxies At Z=3.1: L* Progenitors Experiencing Rapid Star Formation
(2007-12) Gawiser, Eric; Francke, Harold; Lai, Kamson; Schawinski, Kevin; Gronwall, Caryl; Ciardullo, Robin; Quadri, Ryan; Orsi, Alvaro; Barrientos, Felipe; Blanc, Guillermo A.; Fazio, Giovanni; Feldmeier, John J.; Huang, Jia-Sheng; Infante, Leopoldo; Lira, Paulina; Padilla, Nelson; Taylor, E. Nelson; Treister, Ezequiel; Urry, C. Megan; Van Dokkum, Pieter G.; Virani, Shanil N.; Blanc, Guillermo A.
We studied the clustering properties and multiwavelength spectral energy distributions of a complete sample of 162 Ly alpha- emitting (LAE) galaxies at z similar or equal to 3: 1 discovered in deep narrowband MUSYC imaging of the Extended Chandra Deep Field-South. LAEs were selected to have observed frame equivalent widths >80 angstrom and emission line fluxes >1.5 x 10(-17) ergs cm(-2) s(-1). Only 1% of our LAE sample appears to host AGNs. The LAEs exhibit a moderate spatial correlation length of r(0) = 3.6(-1.0)(+0.8) Mpc, corresponding to a bias factor b = 1.7(-0.4)(+0.3), which implies median dark matter halo masses of log(10)M(med) = 10.9(-0.9)(+0.5) M(circle dot). Comparing the number density of LAEs, 1.5 +/- 0.3 x 10(-3) Mpc(-3), with the number density of these halos finds a mean halo occupation similar to 1%-10%. The evolution of galaxy bias with redshift implies that most z 3: 1 LAEs evolve into present-day galaxies with L < 2.5L*, whereas other z > 3 galaxy populations typically evolve into more massive galaxies. Halo merger trees show that z 0 descendants occupy halos with a wide range of masses, with a median descendant mass close to that of L*. Only 30% of LAEs have sufficient stellar mass (>similar to 3 x 10(9) M(circle dot)) to yield detections in deep Spitzer IRAC imaging. A two-population SED fit to the stacked UBVRIzJK+[3.6, 4.5, 5.6, 8.0] mu m fluxes of the IRAC-undetected objects finds that the typical LAE has low stellar mass (1.0(-0.4)(+0.6) 10(9) M(circle dot)), moderate star formation rate (2 +/- 1 M(circle dot) yr(-1)), a young component age of 20(-10)(+30) Myr, and little dust (A(V) < 0: 2). The bestfit model has 20% of the mass in the young stellar component, but models without evolved stars are also allowed.
The Multiwavelength Survey By Yale-Chile (MUSYC) Wide K-Band Imaging, Photometric Catalogs, Clustering, And Physical Properties Of Galaxies At Z Similar To 2
(2008-07) Blanc, Guillermo A.; Lira, Paulina; Barrientos, L. Felipe; Aguirre, Paula; Francke, Harod; Taylor, Edward N.; Quadri, Ryan; Marchesini, Danilo; Infante, Leopoldo; Gawiser, Eric; Hall, Patrick B.; Willis, Jon P.; Herrera, David; Maza, Jose; Blanc, Guillermo A.
We present K-band imaging of two similar to 30' x 30' fields covered by the Multiwavelength Survey by Yale-Chile (MUSYC) Wide NIR Survey. The SDSS 1030+05 and Cast 1255 fields were imaged with the Infrared Side Port Imager (ISPI) on the 4 m Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO) to a 5 sigma point-source limiting depth of K similar to 20 (Vega). Combining these data with the MUSYC optical UBVRIz imaging, we created multiband K-selected source catalogs for both fields. These catalogs, together with the MUSYC K-band catalog of the Extended Chandra Deep Field South (ECDF-S) field, were used to select K 20 BzK galaxies over an area of 0.71 deg(2). This is the largest area ever surveyed for BzK galaxies. We present number counts, redshift distributions, and stellar masses for our sample of 3261 BzK galaxies (2502 star-forming [sBzK] and 759 passively evolving [pBzK]), as well as reddening and star formation rate estimates for the star-forming BzK systems. We also present two-point angular correlation functions and spatial correlation lengths for both sBzK and pBzK galaxies and show that previous estimates of the correlation function of these galaxies were affected by cosmic variance due to the small areas surveyed. We have measured correlation lengths r(0) of 8.89 +/- 2.03 and 10.82 +/- 1.72 Mpc for sBzK and pBzK galaxies, respectively. This is the first reported measurement of the spatial correlation function of passive BzK galaxies. In the Lambda CDM scenario of galaxy formation, these correlation lengths at z similar to 2 translate into minimum masses of similar to 4 x 10(12) and similar to 9 x 10(12) M(circle dot) for the dark matter halos hosting sBzK and pBzK galaxies, respectively. The clustering properties of the galaxies in our sample are consistent with their being the descendants of bright Lyman break galaxies at z similar to 3, and the progenitors of present-day > 1L* galaxies.
Perturbation Theory Reloaded. II. Nonlinear Bias, Baryon Acoustic Oscillations, And Millennium Simulation In Real Space
(2009-01) Jeong, Donghui; Komatsu, Eiichiro; Jeong, Donghui; Komatsu, Eiichiro
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.
Primordial Non-Gaussianity, Scale-Dependent Bias, And The Bispectrum Of Galaxies
(2009-10) Jeong, Donghui; Komatsu, Eiichiro; Jeong, Donghui; Komatsu, Eiichiro
The three-point correlation function of cosmological fluctuations is a sensitive probe of the physics of inflation. We calculate the bispectrum, B(g)(k(1), k(2), k(3)), Fourier transform of the three-point function of density peaks (e.g., galaxies), using two different methods: the Matarrese-Lucchin-Bonometto formula and the locality of galaxy bias. The bispectrum of peaks is not only sensitive to that of the underlying matter density fluctuations, but also to the four-point function. For a physically motivated, local form of primordial non-Gaussianity in the curvature perturbation, Phi = phi + f(NL)phi(2) + g(NL)phi(3), where phi is a Gaussian field, we show that the galaxy bispectrum contains five physically distinct pieces: (1) non-linear gravitational evolution, (2) non-linear galaxy bias, (3) f(NL), (4) f(NL)(2), and (5) g(NL). While (1), (2), and a part of (3) have been derived in the literature, (4) and (5) are derived in this paper for the first time. We also find that, in the high-density peak limit, (3) receives an enhancement of a factor of similar to 15 relative to the previous calculation for the squeezed triangles (k(1) approximate to k(2) approximate to k(3)). Our finding suggests that the galaxy bispectrum is more sensitive to f(NL) than previously recognized, and is also sensitive to a new term, g(NL). For a more general form of local-type non-Gaussianity, the coefficient f(NL)(2) can be interpreted as tau(NL), which allows us to test multi-field inflation models using the relation between the three- and four-point functions. The usual terms from Gaussian initial conditions, (1) and (2), have the smallest signals in the squeezed configurations, while the others have the largest signals; thus, we can distinguish them easily. We cannot interpret the effects of f(NL) on B(g)(k(1), k(2), k(3)) as a scale-dependent bias, and thus replacing the linear bias in the galaxy bispectrum with the scale-dependent bias known for the power spectrum results in an incorrect prediction. As the importance of primordial non-Gaussianity relative to the non-linear gravity evolution and galaxy bias increases toward higher redshifts, galaxy surveys probing a high-redshift universe are particularly useful for probing the primordial non-Gaussianity.
Reconstructing Emission From Pre-Reionization Sources With Cosmic Infrared Background Fluctuation Measurements By The JWST
(2015-05) Kashlinsky, A.; Mather, J. C.; Helgason, K.; Arendt, R. G.; Bromm, Volker; Moseley, S. H.; Bromm, Volker
We present new methodology to use cosmic infrared background (CIB) fluctuations to probe sources at 10 less than or similar to z less than or similar to 30 from a James Webb Space Telescope (JWST)/NIRCam configuration that will isolate known galaxies to 28 AB mag at 0.5-5 mu m. At present significant mutually consistent source-subtracted CIB fluctuations have been identified in the Spitzer and AKARI data at similar to 2-5 mu m, but we demonstrate internal inconsistencies at shorter wavelengths in the recent CIBER data. We evaluate CIB contributions from remaining galaxies and show that the bulk of the high-z sources will be in the confusion noise of the NIRCam beam, requiring CIB studies. The accurate measurement of the angular spectrum of the fluctuations and probing the dependence of its clustering component on the remaining shot noise power would discriminate between the various currently proposed models for their origin and probe the flux distribution of its sources. We show that the contribution to CIB fluctuations from remaining galaxies is large at visible wavelengths for the current instruments precluding probing the putative Lyman-break of the CIB fluctuations. We demonstrate that with the proposed JWST configuration such measurements will enable probing the Lyman-break. We develop a Lyman-break tomography method to use the NIRCam wavelength coverage to identify or constrain, via the adjacent two-band subtraction, the history of emissions over 10 less than or similar to z less than or similar to 30 as the universe comes out of the "Dark Ages." We apply the proposed tomography to the current Spitzer/IRAC measurements at 3.6 and 4.5 mu m, to find that it already leads to interestingly low upper limit on emissions at z greater than or similar to 30.
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: are there Cosmic Microwave Background Anomalies?
(2011-02) Bennett, C. L.; Hill, R. S.; Hinshaw, G.; Larson, D.; Smith, K. M.; Dunkley, J.; Gold, B.; Halpern, M.; Jarosik, N.; Kogut, A.; Komatsu, Eiichiro; Limon, M.; Meyer, S. S.; Nolta, M. R.; Odegard, N.; Page, L.; Spergel, D. N.; Tucker, G. S.; Weiland, J. L.; Wollack, E.; Wright, E. L.; Komatsu, Eiichiro
A simple six-parameter Lambda CDM model provides a successful fit to WMAP data. This holds both when the WMAP data are analyzed alone or in combination with other cosmological data. Even so, it is appropriate to examine the data carefully to search for hints of deviations from the now standard model of cosmology, which includes inflation, dark energy, dark matter, baryons, and neutrinos. The cosmological community has subjected the WMAP data to extensive and varied analyses. While there is widespread agreement as to the overall success of the six-parameter Lambda CDM model, various "anomalies" have been reported relative to that model. In this paper we examine potential anomalies and present analyses and assessments of their significance. In most cases we find that claimed anomalies depend on posterior selection of some aspect or subset of the data. Compared with sky simulations based on the best-fit model, one can select for low probability features of the WMAP data. Low probability features are expected, but it is not usually straightforward to determine whether any particular low probability feature is the result of the a posteriori selection or non-standard cosmology. Hypothesis testing could, of course, always reveal an alternative model that is statistically favored, but there is currently no model that is more compelling. We find that two cold spots in the map are statistically consistent with random cosmic microwave background (CMB) fluctuations. We also find that the amplitude of the quadrupole is well within the expected 95% confidence range and therefore is not anomalously low. We find no significant anomaly with a lack of large angular scale CMB power for the best-fit Lambda CDM model. We examine in detail the properties of the power spectrum data with respect to the Lambda CDM model and find no significant anomalies. The quadrupole and octupole components of the CMB sky are remarkably aligned, but we find that this is not due to any single map feature; it results from the statistical combination of the full-sky anisotropy fluctuations. It may be due, in part, to chance alignments between the primary and secondary anisotropy, but this only shifts the coincidence from within the last scattering surface to between it and the local matter density distribution. While this alignment appears to be remarkable, there was no model that predicted it, nor has there been a model that provides a compelling retrodiction. We examine claims of a hemispherical or dipole power asymmetry across the sky and find that the evidence for these claims is not statistically significant. We confirm the claim of a strong quadrupolar power asymmetry effect, but there is considerable evidence that the effect is not cosmological. The likely explanation is an insufficient handling of beam asymmetries. We conclude that there is no compelling evidence for deviations from the Lambda CDM model, which is generally an acceptable statistical fit to WMAP and other cosmological data.
Third-Order Perturbation Theory With Nonlinear Pressure
(2009-07) Shoji, Masatoshi; Komatsu, Eiichiro; Shoji, Masatoshi; Komatsu, Eiichiro
We calculate the nonlinear matter power spectrum using the third-order perturbation theory without ignoring the pressure gradient term. We consider a semirealistic system consisting of two matter components with and without pressure, and both are expanded into the third order in perturbations in a self-consistent manner, for the first time. While the pressured component may be identified with baryons or neutrinos, in this paper we mainly explore the physics of the nonlinear pressure effect using a toy model in which the Jeans length does not depend on time, i.e., the sound speed decreases as a(-1/2), where a is the scale factor. The linear analysis shows that the power spectrum below the so-called filtering scale is suppressed relative to the power spectrum of the cold dark matter. Our nonlinear calculation shows that the actual filtering scale for a given sound speed is smaller than the linear filtering scale by a factor depending on the redshift and the Jeans length. A similar to 40% change is common, and our results suggest that, when applied to baryons, the temperature of the intergalactic medium inferred from the filtering scale observed in the flux power spectrum of Ly alpha forests would be underestimated by a factor of 2, if one used the linear filtering scale to interpret the data. The filtering mass, which is proportional to the filtering scale cubed, can also be significantly smaller than the linear theory prediction especially at low redshift, where the actual filtering mass can be smaller than the linear prediction by a factor of 3. Finally, when applied to neutrinos, we find that neutrino perturbations deviate significantly from linear perturbations even below the free-streaming scales, and thus neutrinos cannot be treated as linear perturbations.