scholarly journals On the Use of Fractal Concepts in Analysis of Distributions of Galaxies

1996 ◽  
Vol 168 ◽  
pp. 473-475
Author(s):  
I.B. Vavilova
Keyword(s):  
Fractal Structure ◽  
Three Dimensional ◽  
Fractal Pattern ◽  
Galaxy Distribution ◽  
Low Surface Brightness ◽  
The Galaxy ◽  
Good Review ◽  
Dimensional Distribution ◽  
The Universe ◽  
Scaling Index

The well- grounded polemics about the fractal structure of the Universe and a new cosmological picture which appears in connection with this, in first instance the absence of any evidence for homogenization up to present observational limits 200h−1Mpc, have been detailed at the work by Coleman, Pietronero (1992). Two versions on nature of fractal pattern of the galaxy distribution in the observed universe also are now: it behaves like a simple homogeneous fractal (Pietronero 1987; Coleman et al. 1988) and as a multifractal - fractal having more than one scaling index (Jones et al. 1988; Martinez, Jones 1990; Martinez et al. 1990; Borgani et al. 1993 (with the good review for matter of above)).This work does not play decisively into hands of these versions so the fractal concepts, exactly a selfsimilarity and multifractal, were applied here for the analysis oftwo - dimensionaldistribution of thebrightgalaxies and dwarf galaxies of the low surface brightness (LSBD) belonging to the Local Supercluster (LS). But if the observed universe holds the fractal structure, so it is useful to trace over the lower fractal pattern on the small scales of clustering of galaxies within the framework of the known superclusters and, in the first instance, within the local overdensity of galaxies. This work is a preliminary before preparing one with the same analysis of three- dimensional distribution of galaxies of LS.

scholarly journals On the Fractal Structure of Galaxy Distribution and its Implications for Cosmology

Fractals ◽  
1998 ◽  
Vol 06 (03) ◽  
pp. 231-243 ◽  
Author(s):  
Yurij V. Baryshev ◽  
Francesco Sylos Labini ◽  
Marco Montuori ◽  
Luciano Pietronero ◽  
Pekka Teerikorpi
Keyword(s):  
Large Scale ◽  
Fractal Structure ◽  
Three Dimensional ◽  
Space Distribution ◽  
Large Scale Structures ◽  
Galaxy Distribution ◽  
Standard Cosmology ◽  
Dimensional Distribution ◽  
Scale Structures ◽  
Distance Relation

Two fundamental empirical laws have been established in the analysis of galaxy space distribution. First, recent analyses have revealed that the three-dimensional distribution of galaxies and clusters is characterized by large-scale structures and huge voids: such a distribution shows fractal correlations up to the limits of the available samples. This has confirmed the earlier de Vaucouleurs power-law density — distance relation, now corresponding to a fractal structure with dimension D ≈ 2, at least, in the range of scales ~1 ÷ 200 Mpc (H0=55 km/sec/Mpc). An eventual cut-off towards homogenization has not been yet identified. Second, since Huble's discovery, the linear redshift-distance law has been well established within 200 Mpc and also much deeper. The co-existence of these laws within the same scales is a challenge for the standard cosmology, where the linear Hubble law is a strict consequence of homogeneity of the expanding universe. This puzzle is now sufficiently strong to raise doubts for the standard cosmology.

scholarly journals Inferring the three-dimensional distribution of dust in the Galaxy with a non-parametric method

2017 ◽  
Vol 598 ◽  
pp. A125 ◽  
Author(s):  
S. Rezaei Kh. ◽  
C. A. L. Bailer-Jones ◽  
R. J. Hanson ◽  
M. Fouesneau
Keyword(s):  
Parametric Method ◽  
Three Dimensional ◽  
The Galaxy ◽  
Dimensional Distribution ◽  
Non Parametric

scholarly journals Clustering, Isotropy, and Redshift Cutoff

1986 ◽  
Vol 119 ◽  
pp. 447-454
Author(s):  
Patrick S. Osmer
Keyword(s):  
Optical Depth ◽  
Three Dimensional ◽  
Radial Distance ◽  
Specific Question ◽  
Dimensional Distribution ◽  
Steep Decline ◽  
Age Of The Universe ◽  
Short Time ◽  
The Universe ◽  
Luminosity Evolution

The topics of clustering, isotropy, and redshift cutoff are in reality just different aspects of the problem of the three-dimensional distribution of quasars, assuming, of course that the redshifts are cosmological and therefore an indication of radial distance. The distribution in redshift has additional interest because of the substantial lookback times involved, up to four fifths of the age of the universe. The radial variation of quasar density between redshift zero and two, and the attendant questions of density and luminosity evolution, are discussed elsewhere in this symposium by Green and shall not be treated here. Rather we shall concern ourselves with the behavior at redshifts larger than two and the specific question of a steep decline of quasar density at redshifts near three. For simplicity we may characterize the problem as one of studying either the formation of quasars as we normally see them in a cosmologically short time or of the properties of the universe and its optical depth, should intergalactic absorption contribute significantly to blocking our view at redshift three. Of course other hypotheses are also possible.

scholarly journals Characterising filaments in the SDSS volume from the galaxy distribution

2020 ◽  
Vol 642 ◽  
pp. A19 ◽  
Author(s):  
Nicola Malavasi ◽  
Nabila Aghanim ◽  
Marian Douspis ◽  
Hideki Tanimura ◽  
Victor Bonjean
Keyword(s):  
Large Scale ◽  
Sloan Digital Sky Survey ◽  
Specific Method ◽  
Redshift Surveys ◽  
Galaxy Distribution ◽  
Systematic Uncertainties ◽  
Sky Survey ◽  
The Galaxy ◽  
Free Parameters ◽  
The Universe

Detecting the large-scale structure of the Universe based on the galaxy distribution and characterising its components is of fundamental importance in astrophysics but is also a difficult task to achieve. Wide-area spectroscopic redshift surveys are required to accurately measure galaxy positions in space that also need to cover large areas of the sky. It is also difficult to create algorithms that can extract cosmic web structures (e.g. filaments). Moreover, these detections will be affected by systematic uncertainties that stem from the characteristics of the survey used (e.g. its completeness and coverage) and from the unique properties of the specific method adopted to detect the cosmic web (i.e. the assumptions it relies on and the free parameters it may employ). For these reasons, the creation of new catalogues of cosmic web features on wide sky areas is important, as this allows users to have at their disposal a well-understood sample of structures whose systematic uncertainties have been thoroughly investigated. In this paper we present the filament catalogues created using the discrete persistent structure extractor tool in the Sloan Digital Sky Survey (SDSS), and we fully characterise them in terms of their dependence on the choice of parameters pertaining to the algorithm, and with respect to several systematic issues that may arise in the skeleton as a result of the properties of the galaxy distribution (such as Finger-of-God redshift distortions and defects of the density field that are due to the boundaries of the survey).

Statistical studies of the spatial distribution of galaxies

1996 ◽  
Vol 28 (02) ◽  
pp. 337-338
Author(s):  
Vicent J. Martínez ◽  
María Jesús Pons-Bordería
Keyword(s):  
Spatial Distribution ◽  
Structure Formation ◽  
Statistical Study ◽  
Three Dimensional ◽  
Dimensional Distribution ◽  
Statistical Studies ◽  
The Universe ◽  
Clustering Patterns

The statistical study of the clustering patterns formed by the three-dimensional distribution of galaxies is one of the most important observational clues to discriminate between rival theories of structure formation in the Universe.

scholarly journals Is the Universe homogeneous?

2011 ◽  
Vol 369 (1957) ◽  
pp. 5115-5137 ◽  
Author(s):  
Roy Maartens
Keyword(s):  
Cosmic Microwave Background ◽  
Light Cone ◽  
Space Time ◽  
Gravity Models ◽  
Microwave Background ◽  
The Past ◽  
Galaxy Distribution ◽  
The Galaxy ◽  
The Universe ◽  
Past Light Cone

The standard model of cosmology is based on the existence of homogeneous surfaces as the background arena for structure formation. Homogeneity underpins both general relativistic and modified gravity models and is central to the way in which we interpret observations of the cosmic microwave background (CMB) and the galaxy distribution. However, homogeneity cannot be directly observed in the galaxy distribution or CMB, even with perfect observations, since we observe on the past light cone and not on spatial surfaces. We can directly observe and test for isotropy, but to link this to homogeneity we need to assume the Copernican principle (CP). First, we discuss the link between isotropic observations on the past light cone and isotropic space–time geometry: what observations do we need to be isotropic in order to deduce space–time isotropy? Second, we discuss what we can say with the Copernican assumption. The most powerful result is based on the CMB: the vanishing of the dipole, quadrupole and octupole of the CMB is sufficient to impose homogeneity. Real observations lead to near-isotropy on large scales—does this lead to near-homogeneity? There are important partial results, and we discuss why this remains a difficult open question. Thus, we are currently unable to prove homogeneity of the Universe on large scales, even with the CP. However, we can use observations of the cosmic microwave background, galaxies and clusters to test homogeneity itself.

scholarly journals The 3-Dimensional Distribution of Interstellar Dust

2013 ◽  
Vol 9 (S298) ◽  
pp. 213-220
Author(s):  
Jayant Murthy
Keyword(s):  
Interstellar Dust ◽  
Three Dimensional ◽  
3 Dimensional ◽  
Dust Extinction ◽  
Structure And Morphology ◽  
Current State ◽  
The Galaxy ◽  
Dimensional Distribution ◽  
Color Data ◽  
Dust Distribution

AbstractA knowledge of the three dimensional distribution of interstellar dust is critical in interpreting all observations of the sky, particularly in the understanding of the structure and morphology of our Galaxy. It has been much easier to map the integrated dust extinction through the Galaxy, which is needed in modeling extragalactic sources, but this yields an overestimate of reddening to Galactic objects. Massive surveys, such as Gaia, present both a problem in that the distribution of interstellar dust must be known in order to model the internal structure of the Galaxy and an opportunity in that multi-color data may be used to deconvolve the dust distribution. I will present the current state of the modeling, which is yet in its early stages.

scholarly journals The intergalactic medium in the cosmic web

2014 ◽  
Vol 11 (S308) ◽  
pp. 364-367
Author(s):  
Nicolas Tejos
Keyword(s):  
Intergalactic Medium ◽  
Three Dimensional ◽  
Baryonic Matter ◽  
One Dimensional ◽  
Star Forming ◽  
Galaxy Surveys ◽  
Dimensional Distribution ◽  
Formation And Evolution ◽  
The Universe ◽  
Cross Matching

AbstractThe intergalactic medium (IGM) accounts for ≳ 90% of baryons at all epochs and yet its three dimensional distribution in the cosmic web remains mostly unknown. This is so because the only feasible way to observe the bulk of the IGM is through intervening absorption line systems in the spectra of bright background sources, which limits its characterization to being one-dimensional. Still, an averaged three dimensional picture can be obtained by combining and cross-matching multiple one-dimensional IGM information with three-dimensional galaxy surveys. Here, we present our recent and current efforts to map and characterize the IGM in the cosmic web using galaxies as tracers of the underlying mass distribution. In particular, we summarize our results on: (i) IGM around star-forming and non-star-forming galaxies; (ii) IGM within and around galaxy voids; and (iii) IGM in intercluster filaments. With these datasets, we can directly test the modern paradigm of structure formation and evolution of baryonic matter in the Universe.

scholarly journals Determining Ω0 and λ0 from Cosmological Redshift Distortion of Galaxies and Quasars

1999 ◽  
Vol 183 ◽  
pp. 235-240
Author(s):  
Yasushi Suto
Keyword(s):  
Large Scale ◽  
Collaborative Work ◽  
Cosmological Parameters ◽  
Three Dimensional ◽  
Density Parameter ◽  
Cosmological Redshift ◽  
Peculiar Velocity ◽  
Dimensional Distribution ◽  
Space Distortion ◽  
The Universe

The three-dimensional distribution of galaxies in the redshift surveys differ from the true one since the distance to each galaxy cannot be determined by its redshift z only; for z ≪ 1 the peculiar velocity of galaxies, typically ∼ (100–1000)km/sec, contaminates the true recession velocity of the Hubble flow, while the true distance for objects at z ≳ 1 sensitively depends on the (unknown and thus assumed) cosmological parameters. This hampers the effort to understand the true distribution of large-scale structure of the universe. Nevertheless such redshift-space distortion effects are quite useful since through the detailed theoretical modeling, one can derive the peculiar velocity dispersions of galaxies as a function of separation, and also can infer the cosmological density parameter Ω0, the dimensionless cosmological constant λ0, and the spatial biasing factor b of galaxies and/or quasars, for instance. In this talk, I discuss the importance of such redshift distortion induced by the geometry of the universe, which summarizes the recent results of my collaborative work in this topic (Matsubara & Suto 1996; Nakamura, Matsubara, & Suto 1998; Magira, Matsubara, Jing, & Suto 1998).

scholarly journals Optical Redshift Surveys

1992 ◽  
Vol 9 ◽  
pp. 681-683
Author(s):  
L. Nicolaci da Costa
Keyword(s):  
Large Scale ◽  
Current Status ◽  
Redshift Surveys ◽  
Galaxy Distribution ◽  
The Galaxy ◽  
Redshift Survey ◽  
Different Depths ◽  
Source Of Information ◽  
The Universe

Redshift surveys of galaxies have been over the past decade the major source of information for studies of the large-scale structure of the Universe. Following the completion of the original CfA Redshift Survey, several groups have joined the endeavor, probing different regions of the sky to different depths in a remarkable long-term effort to study the nature of the galaxy distribution and its statistical properties at different scales. Here I summarize the current status of the ongoing surveys drawn from optical galaxy catalogs. The review is not intended to be complete but rather to demonstrate the vitality of the area and to point out that exciting new data should be forthcoming in the next few years.

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