Large-scale Structure Of Universe Research Articles

The Line-of-Sight Analysis of Spatial Distribution of Galaxies in the COSMOS2015 Catalogue

New observations of high-redshift objects are crucial for the improvement of the standard ΛCDM cosmological model and our understanding of the Universe. One of the main directions of modern observational cosmology is the analysis of the large-scale structure of Universe, in particular, in deep fields. We study the large-scale structure of the Universe along the line of sight using the latest version of the COSMOS2015 catalogue, which contains 518,404 high quality photometric redshifts of galaxies selected in the optical range of the COSMOS field (2×2 deg2), with depth up to the redshift z∼6. We analyze large-scale fluctuations in the number of galaxies along the line of sight and provide an estimate of the average linear sizes of the self-correlating fluctuations (structures) in independent redshift bins of Δz=0.1 along with the estimate of the standard deviation from homogeneity (the observed cosmic variance). We suggest a new method of the line-of-sight analysis based on previous works and formulate further prospects of method development. For the case of the theoretical form of approximation of homogeneity in the ΛCDM framework, the average standard deviation of detected structures from homogeneity is σmeanΛCDM=0.09±0.02, and the average characteristic size of structures is RmeanΛCDM=790±150 Mpc. For the case of the empirical approximation of homogeneity, the average standard deviation of detected structures from homogeneity is σmeanempiric=0.08±0.01, and the average characteristic size of structures is Rmeanempiric=640±140 Mpc.

Reconstructing the Inflationary Landscape with Cosmological Data.

We show that the shape of the inflationary landscape potential may be constrained by analyzing cosmological data. The quantum fluctuations of fields orthogonal to the inflationary trajectory may have probed the structure of the local landscape potential, inducing non-Gaussianity (NG) in the primordial distribution of the curvature perturbations responsible for the cosmic microwave background (CMB) anisotropies and our Universe's large-scale structure. The resulting type of NG (tomographic NG) is determined by the shape of the landscape potential, and it cannot be fully characterized by 3- or 4-point correlation functions. Here we deduce an expression for the profile of this probability distribution function in terms of the landscape potential, and we show how this can be inverted in order to reconstruct the potential with the help of CMB observations. While current observations do not allow us to infer a significant level of tomographic NG, future surveys may improve the possibility of constraining this class of primordial signatures.

Bin recycling strategy for improving the histogram precision on GPU

Histogram is an easily comprehensible way to present data and analyses. In the current scientific context with access to large volumes of data, the processing time for building histogram has dramatically increased. For this reason, parallel construction is necessary to alleviate the impact of the processing time in the analysis activities. In this scenario, GPU computing is becoming widely used for reducing until affordable levels the processing time of histogram construction. Associated to the increment of the processing time, the implementations are stressed on the bin-count accuracy. Accuracy aspects due to the particularities of the implementations are not usually taken into consideration when building histogram with very large data sets. In this work, a bin recycling strategy to create an accuracy-aware implementation for building histogram on GPU is presented. In order to evaluate the approach, this strategy was applied to the computation of the three-point angular correlation function, which is a relevant function in Cosmology for the study of the Large Scale Structure of Universe. As a consequence of the study a high-accuracy implementation for histogram construction on GPU is proposed.

Halo mass distribution reconstruction across the cosmic web

ABSTRACT We study the relation between halo mass and its environment from a probabilisticperspective. We nd that halo mass depends not only on local dark matter density,but also on non-local quantities such as the cosmic web environment and the halo-exclusion e ect. Given these accurate relations, we have developed the hadron-code(Halo mAss Distribution ReconstructiON), a technique which permits us to assignhalo masses to a distribution of haloes in three-dimensional space. This can be ap-plied to the fast production of mock galaxy catalogues, by assigning halo masses,and reproducing accurately the bias for di erent mass cuts. The resulting clusteringof the halo populations agree well with that drawn from the BigMultiDark N-bodysimulation: the power spectra are within 1-˙up to scales of k= 0:2hMpc 1 , whenusing augmented Lagrangian perturbation theory based mock catalogues. Only themost massive haloes show a larger deviation. For these, we nd evidence of the halo-exclusion e ect. A clear improvement is achieved when assigning the highest massesto haloes with a minimum distance separation. We also compute the 2- and 3-pointcorrelation functions, and nd an excellent agreement with N-body results. Our workrepresents a quantitative application of the cosmic web classi cation. It can have fur-ther interesting applications in the multi-tracer analysis of the large-scale structurefor future galaxy surveys.Key words: (cosmology:) large-scale structure of Universe { galaxies: clusters: gen-eral { catalogues { galaxies: statistics

The cross-correlation of Mg ii absorption and galaxies in BOSS

We present a measurement of the cross-correlation of MgII absorption and massive galaxies, using the DR11 main galaxy sample of the Baryon Oscillation Spectroscopic Survey of SDSS-III (CMASS galaxies), and the DR7 quasar spectra of SDSS-II. The cross-correlation is measured by stacking quasar absorption spectra shifted to the redshift of galaxies that are within a certain impact parameter bin of the quasar, after dividing by a quasar continuum model. This results in an average MgII equivalent width as a function of impact parameter from a galaxy, ranging from 50 kpc to more than 10 Mpc in proper units, which includes all MgII absorbers. We show that special care needs to be taken to use an unbiased quasar continuum estimator, to avoid systematic errors in the measurement of the mean stacked MgII equivalent width. The measured cross-correlation follows the expected shape of the galaxy correlation function, although measurement errors are large. We use the cross-correlation amplitude to derive the bias factor of MgII absorbers, finding bMgII = 2.33 \pm? 0.19, where the error accounts only for the statistical uncertainty in measuring the mean equivalent width. This bias factor is larger than that obtained in previous studies and may be affected by modeling uncertainties that we discuss, but if correct it suggests that MgII absorbers at redshift z \simeq 0:5 are spatially distributed on large scales similarly to the CMASS galaxies in BOSS. Keywords: galaxies: haloes, galaxies: formation, quasars: absorption lines, large-scale structure of universe

An appraisal of Milgrom’s fitting formula by the antigraviton-graviton theory

On one hand, the Wongs antigraviton-graviton theory (AGT), which may also be called a new quantum gravity theory, predicts that at the limit of infinite radius, the effective acceleration is proportional to the square root of the Newtonian gravitational acceleration. Thus it partially supports Milgroms fitting formula (MIFF). On the other hand, our AGT discovers that the definition of the critical acceleration as a universal parameter by MIFF is not adequately valid. Keywords: Cosmology: Theory, Dark Matter, Galaxies: Kinematics And Dynamics, Gravitation, Large-Scale Structure Of Universe.

Discovery of the antigraviton verified by the rotation curve of NGC 6503

Using special relativity theory, it was discovered that to each graviton, there coexists its antiparticle, an antigraviton. Building on this discovery and quantum theory, a new quantum gravity theory (QGT) was invented, providing equations of the gravitational potential, the graviton wavelength, and the circular speed, without the dark matter hypothesis (DMH). According to this QGT, the gravitational scale-length of a spiral galaxy depends on its mass distribution, being approximately equal to 1.5708 times the radius of its “radial center of mass”. Also Newtonian gravity theory (NGT) is of limited validity: if the radius is less than the gravitational scale-length, NGT is exact; but if the radius is greater than the gravitational scale-length, it becomes inadequate, and is surpassed by QGT. When the theoretical rotation curve was compared with the rotation curve of the galaxy NGC6503, the QGT was verified within the rms error of the measured rotation speeds, 3.0 percent. It was also demonstrated how two formulas of general relativity theory (Schwarzschild metric, gravitational time dilation) may be revised by the QGT, and thus be upgraded to formulas of quantum general relativity theory. It is suggested the so-called “dark matter” problem can be solved by discarding the DMH and adopting our new QGT. Keywords: Cosmology: Theory, Dark Matter, Galaxies: Kinematics and Dynamics, Galaxies: Individual (NGC6503), Gravitation, Large-Scale Structure of Universe.

Beyond concordance cosmology with magnification of gravitational-wave standard sirens.

We show how future gravitational-wave detectors would be able to discriminate between the concordance Λ cold dark matter cosmological model and up-to-date competing alternatives, e.g., dynamical dark energy (DE) models or modified gravity (MG) theories. Our method consists of using the weak-lensing magnification effect that affects a standard-siren signal because of its traveling through the Universe's large scale structure. As a demonstration, we present constraints on DE and MG from proposed gravitational-wave detectors, namely Einstein Telescope and DECI-Hertz Interferometer Gravitational-Wave Observatory and Big-Bang Observer.

Propagation of Ultra–High‐Energy Protons through the Magnetized Cosmic Web

If ultraYhigh-energy cosmic rays (UHECRs) originate from extragalactic sources, understanding the propagation of charged particles through the magnetized large-scale structure (LSS) of the universe is crucial in the search for the astrophysical accelerators. Based on a novel model of the turbulence dynamo, we estimate the intergalactic magnetic fields (IGMFs) in cosmological simulations of the formation of the LSS. Under the premise that the sources of UHECRs are strongly associated with the LSS, we consider a model in which protons with E � 10 19 eVare injected by sources that represent active galactic nuclei, located inside clusters of galaxies. With the model IGMFs, we then follow the trajectories of the protons, taking into account the energy losses due to interactions with the cosmic background radiation. For observers located inside groups of galaxies like ours, about 70% and 35% of UHECR events above 60 EeVarrive within � 15 � and � 5 � , respectively, of the source position with time delays of less than � 10 7 yr. This implies that the arrival direction of super-GZK protons might exhibit a correlation with the distribution of cosmologicalsourcesonthesky.Inthismodel,nearbysources(within10Y20Mpc)shouldcontributesignificantlytothe particle flux above � 10 20 eV. Subject headingg cosmic rays — large-scale structure of universe — magnetic fields — methods: numerical

The Halo Mass‐Bias Redshift Evolution in the ΛCDM Cosmology

We derive an analytic model for the redshift evolution of linear-bias, allowing for interactions and merging of the mass-tracers, by solving a second order differential equation based on linear perturbation theory and the Friedmann-Lemaitre solutions of the cosmological field equations. We then study the halo- mass dependence of the bias evolution, using the dark matter halo distribution in aCDM simulation in order to calibrate the free parameters of the model. Finally, we compare our theoretical predictions with available observational data and find a good agreement. In particular, we find that the bias of optical QSO's evolve differently than those selected in X-rays and that their corresponding typical dark matter halo mass is ∼ 10 13 h −1 M⊙ and ∼ 5 × 10 13 h −1 M⊙, respectively. Subject headings: cosmology: theory - dark matter - galaxies: halos - galaxies: formation - large-scale structure of universe - methods: N-body simulations.

The MaximumB‐Mode Polarization of the Cosmic Microwave Background from Inhomogeneous Reionization

We compute the B-mode polarization power spectrum of the CMB from an epoch of inhomogeneous reionization, using a simple model in which H II regions are represented by ionized spherical bubbles with a log normal distribution of sizes whose clustering properties are determined by large-scale structure. Both the global ionization fraction and the characteristic radius of H II regions are allowed to be free functions of redshift. Models that would produce substantial contamination to degree scale gravitational wave B-mode measurements have power that is dominated by the shot noise of the bubbles. Rare bubbles of & 100 Mpc at z > 20 can produce signals that in fact exceed the B-modes from gravitational lensing and are comparable to the maximal allowed signal of gravitational waves (∼ 0.1 � K) while still being consistent with global constraints on the total optical depth. Even bubbles down to 20 Mpc at z ∼ 15, or 40 Mpc at z ∼ 10 can be relevant (0.01 � K) once the lensing signal is removed either statistically or directly. However, currently favored theoretical models that have ionization bubbles that only grow to such sizes at the very end of a fairly prompt and late reionization produce signals which are at most at these levels. Subject headings: cosmic microwave background — cosmology: theory — large-scale structure of universe

On the Putative Detection ofz> 0 X‐Ray Absorption Features in the Spectrum of Mrk 421

In a series of papers, Nicastro et al. have reported the detection of z > 0O vii absorption features in the spectrum of Mrk421obtainedwiththeChandraLowEnergyTransmissionGratingSpectrometer(LETGS).Weevaluatethisresult in the context of a high-quality spectrum of the same source obtained with the Reflection Grating Spectrometer (RGS) onXMM-Newton.Thedatacompriseover955ksof usableexposuretimeandmorethan2:6 ; 10 4 countsper50m8at 21.68.Weconcentrateonthespectrallycleanregion(21:3 < k < 22:5),wheresharpfeaturesduetotheastrophysically abundant O vii may reveal an intervening, warm-hot intergalactic medium (WHIM). We do not confirm detection of any of the intervening systems claimed to date. Rather, we detect only three unsurprising, astrophysically expected features down to the log(Ni) � 14:6(3� ) sensitivity level. Each of the two purported WHIM features is rejected with a statistical confidence that exceeds that reported for its initial detection. While we cannot rule out the existence of fainter, WHIM related features in these spectra, we suggest that previous discovery claims were premature. A more recentpaperbyWilliamsetal.claimstohavedemonstratedthattheRGSdataweanalyzeheredonothavetheresolution or statistical quality required to confirm or deny the LETGS detections. We show that our analysis resolves the issues encountered by Williams et al. and recovers the full resolution and statistical quality of the RGS data. We highlight the differences between our analysis and those published by Williams et al. as this may explain our disparate conclusions. Subject headingg intergalactic medium — large-scale structure of universe — methods: data analysis — techniques: spectroscopic — telescopes — X-rays: diffuse background

The DEEP2 Galaxy Redshift Survey: the relationship between galaxy properties and environment at z 1

We study the mean environment of galaxies in the DEEP2 Galaxy Redshift Survey as a function of rest-frame color, luminosity, and [OII] 3727u equivalent width. The local galaxy overdensity for > 14,000 galaxies at 0.75 < z < 1.35 is estimated using the projected 3 rd -nearest-neighbor surface density. Of the galaxy properties studied, mean environment is found to depend most strongly on galaxy color; all major features of the correlation between mean overdensity and rest-frame color observed in the local universe were already in place at z ∼ 1. In contrast to local results, we find a substantial slope in the mean dependence of environment on luminosity for blue, star-forming galaxies at z ∼ 1, with brighter blue galaxies being found on average in regions of greater overdensity. We discuss the roles of galaxy clusters and groups in establishing the observed correlations between environment and galaxy properties at high redshift, and we also explore the evidence for a “downsizing of quenching” from z ∼ 1 to z ∼ 0. Our results add weight to existing evidence that the mechanism(s) that result in star-formation quenching are efficient in group environments as well as clusters. This work is the first of its kind at high redshift and represents the first in a series of papers addressing the role of environment in galaxy formation at 0 < z < 1. Subject headings: galaxies:high-redshift, galaxies:evolution, galaxies:statistics, galaxies:fundamental parameters, large-scale structure of universe

Probing the bispectrum at high redshifts using 21-cm H I observations

ABSTRACT Observations of fluctuations in the redshifted 21 cm radiation from neutral hydrogen(HI) are perceived to be an important future probe of the universe at high redshifts.Under the assumption that at redshifts z ≤ 6 (Post-Reionization Era) the HI tracesthe underlying dark matter with a possible bias, we investigate the possibility of usingobservations of redshifted 21 cm radiation to detect the bispectrum arising from non-linear gravitational clustering and from non-linear bias. We find that the expectedsignal is ∼ 0.1mJy at 325MHz (z = 3.4) for the small baselines at the GMRT, thestrength being a few times largerat higher frequencies (610MHz,z = 1.3). Further, themagnitude ofthe signalfromthe bispectrum is predictedto be comparabletothat fromthe power spectrum, allowing a detection of both in roughly the same integration time.The HI signal is found to be uncorrelated beyond frequency separations of ∼ 1.3MHzwhereas the continuum sources of continuum are expected to be correlated acrossmuch larger frequencies. This signature can in principle be used to distinguish the HIsignal from the contamination. We also consider the possibility of using observationsof the bispectrum to determine the linear and quadratic bias parameters of the HI athigh redshifts, this having possible implications for theories of galaxy formation.Key words: cosmology: large scale structure of universe - intergalactic medium -diffuse radiation

The XMM Large-Scale Structure survey: an initial sample of galaxy groups and clusters to a redshift z &lt; 0.6

We present X-ray and optical spectroscopic observations of 12 galaxy groups and clusters identified within the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey. Groups and clusters are selected as extended X-ray sources from a 3.5 deg 2 XMM image mosaic above a flux limit 8 × 10 −15 erg s −1 cm −2 in the [0.5‐2] keV energy band. Deep BVRI images and multi-object spectroscopy confirm each source as a galaxy concentration located within the redshift interval 0.29 < z < 0.56. We combine line-of-sight velocity dispersions with the X-ray properties of each structure computed from a two-dimensional surface brightness model and a single temperature fit to the XMM spectral data. The resulting distribution of X-ray luminosity, temperature and velocity dispersion indicate that the XMM‐LSS survey is detecting low-mass clusters and galaxy groups to redshifts z < 0.6. Confirmed systems display little or no evidence for X-ray luminosity evolution at a given X-ray temperature compared to lower-redshift X-ray group and cluster samples. A more complete understanding of these trends will be possible with the compilation of a statistically complete sample of galaxy groups and clusters anticipated within the continuing XMM‐LSS survey. Ke yw ords: surveys ‐ large-scale structure of Universe ‐ X-rays: galaxies: clusters.

Dark energy and dark matter haloes

We investigate the effect of dark energy on the density profiles of dark matter haloes with a suite of cosmological N-body simulations and use our results to test analytic models. We consider constant equation of state models, and allow both w −1 and w −1 quintessence models seem to exacerbate the central density problem relative to the standard w =− 1 model. Fo re xample, models with w �− 0.5 seem disfavoured by the data, which can be matched only by allowing extremely low normalizations, σ 8 0.6. Meanwhile w< −1 models help to reduce the apparent discrepancy. We confirm that the halo mass function of Jenkins et al. provides an excellent approximation to the abundance of haloes in our simulations and extend its region of validity to include models with w< −1. Ke yw ords: methods: N-body simulations ‐ cosmology: theory ‐ dark matter ‐ large-scale structure of Universe.

Large-scale bias and stochasticity of haloes and dark matter

On large scales, galaxies and their haloes are usually assumed to trace the dark matter with a constant bias and dark matter is assumed to trace the linear density field. We test these assumption using several large N-body simulations with 384 3 ‐1024 3 particles and box sizes of 96‐1152 h −1 Mpc, which can both resolve the small galactic-size haloes and sample the large-scale fluctuations. We explore the average halo bias relation as a function of halo mass and show that existing fitting formulae overestimate the halo bias by up to 20 per cent in the regime just below the non-linear mass. We propose a new expression that fits our simulations well. We find that the halo bias is nearly constant, b ∼ 0.65‐0.7, for masses below one-tenth of the non-linear mass. We next explore the relation between the initial and final dark matter in individual Fourier modes and show that there are significant fluctuations in their ratio, ranging from 10 per cent rms at k ∼ 0.03 h Mpc −1 to 50 per cent rms at k ∼ 0.1 h Mpc −1 .W e a rgue that these large fluctuations are caused by perturbative effects beyond the linear theory, which are dominated by long-wavelength modes with large random fluctuations. Similar or larger fluctuations exist between haloes and dark matter and between haloes of different mass. These fluctuations must be included in attempts to determine the relative bias of two populations from their maps, which would otherwise be immune to sampling variance. Ke yw ords: cosmology: theory ‐ dark matter ‐ large-scale structure of Universe.

Isocurvature fluctuations induce early star formation

The early reionization of the Universe inferred from the WMAP polarization results, if confirmed, poses a problem for the hypothesis that scale-invariant adiabatic density fluctuations account for large-scale structure and galaxy formation. One can only generate the required amount of early star formation if extreme assumptions are made about the efficiency and nature of early reionization. We develop an alternative hypothesis that invokes an additional component of a non-scale-free isocurvature power spectrum together with the scale-free adiabatic power spectrum for inflation-motivated primordial density fluctuations. Such a component is constrained by the Lyman alpha forest observations, can account for the small-scale power required by spectroscopic gravitational lensing, and yields a source of early star formation that can reionize the Universe at z ∼ 20 yet becomes an inefficient source of ionizing photons by z ∼ 10, thereby allowing the conventional adiabatic fluctuation component to reproduce the late thermal history of the intergalactic medium. Ke yw ords: stars: formation ‐ galaxies: formation ‐ intergalactic medium ‐ cosmology: theory ‐ early Universe ‐ large-scale structure of Universe

Interpreting the Observed Clustering of Red Galaxies atz∼ 3

Daddi et al. have recently reported strong clustering of a population of red galaxies at z � 3 in the Hubble Deep Field-South. Fitting the observed angular clustering with a power law of index � 0.8, they infer a comoving correlation length r0 � 8 h � 1 Mpc; for a standard cosmology, this r0 would imply that the red galaxies reside in rare, M � 10 13 h � 1 Mhalos, with each halo hosting � 100 galaxies to match the number density of the pop- ulation. Using the framework of the halo occupation distribution (HOD) in a CDM universe, we show that the Daddi et al. data can be adequately reproduced by less surprising models, e.g., models with galaxies residing in halos of mass M > Mmin ¼ 6:3;10 11 h � 1 Mand a mean occupation Navg(M) ¼ 1:4(M =Mmin) 0:45 above this cutoff. The resultant correlation functions do not follow a strict power law, showing instead a clear transition from the one-halo-dominated regime, where the two galaxies of each pair reside in the same dark matter halo, to the two-halo-dominated regime, where the two galaxies of each pair are from different halos. The observed high- amplitude data points lie in the one-halo-dominated regime, so these HOD models are able to explain the observations despite having smaller correlation lengths, r0 � 5 h � 1 Mpc. HOD parameters are only loosely constrained by the current data because of large sample variance and the lack of clustering information on scales that probe the two-halo regime. If our explanation of the data is correct, then future observations covering a larger area should show that the large-scale correlations lie below a � � 1:8 extrapolation of the small-scale points. Our models of the current data suggest that the red galaxies are somewhat more strongly clustered than UV-selected Lyman break galaxies and have a greater tendency to reside in small groups. Subject heading gs: galaxies: halos — galaxies: high-redshift — large-scale structure of universe

Physical effects on the Lyα forest flux power spectrum: damping wings, ionizing radiation fluctuations and galactic winds

We explore several physical effects on the power spectrum of the Lyα forest transmitted flux. The effects we investigate here are not usually part of hydrodynamic simulations and so need to be estimated separately. The most important effect is that of high column density absorbers with damping wings, which add power on large scales. We compute their effect using the observational constraints on their abundance as a function of column density. Ignoring their effect leads to an underestimation of the slope of the linear theory power spectrum. The second effect we investigate is that of fluctuations in the ionizing radiation field. For this purpose we use a very large high-resolution N-body simulation, which allows us to simulate both the fluctuations in the ionizing radiation and the small-scale Lyα forest within the same simulation. We find an enhancement of power on large scales for quasars and a suppression for galaxies. The strength of the effect rapidly increases with increasing redshift, allowing it to be uniquely identified in cases where it is significant. We develop templates that can be used to search for this effect as a function of quasar lifetime, quasar luminosity function and attenuation length. Finally, we explore the effects of galactic winds using hydrodynamic simulations. We find the wind effects on the Lyα forest power spectrum to be degenerate with parameters related to the temperature of the gas that are already marginalized over in cosmological fits. While more work is needed to conclusively exclude all possible systematic errors, our results suggest that, in the context of data analysis procedures, where parameters of the Lyα forest model are properly marginalized over, the flux power spectrum is a reliable tracer of cosmological information. Ke yw ords: galaxies: high-redshift ‐ intergalactic medium ‐ quasars: absorption lines ‐ cosmology: theory ‐ diffuse radiation ‐ large-scale structure of Universe.