scholarly journals Cosmic voids uncovered – first-order statistics of depressions in the biased density field

2019 ◽  
Vol 488 (4) ◽  
pp. 5075-5084 ◽  
Author(s):  
T Ronconi ◽  
S Contarini ◽  
F Marulli ◽  
M Baldi ◽  
L Moscardini

ABSTRACT Cosmic voids occupy most of the volume of the Universe, and their statistical properties can be exploited for constraining dark energy, as well as for testing theories of gravity. Nevertheless, in spite of their growing popularity as cosmological probes, a gap of knowledge between cosmic void observations and theory still persists. In particular, the void size function models proposed in literature have been proven unsuccessful in reproducing the results obtained from cosmological simulations in which cosmic voids are detected from biased tracers of the density field. The goal of this work is to cover this gap. In particular, we make use of the findings of a previous work in which we have improved the void selection procedure, presenting an algorithm that redefines the void ridges and, consequently, their radii. By applying this algorithm, we validate the volume conserving model of the void size function on a set of unbiased simulated density field tracers. We highlight the difference in the internal structure between voids selected in this way and those identified by the popular vide void finder. We also extend the validation of the model to the case of biased tracers. We find that a relation exists between the tracer used to sample the underlying dark matter density field and its unbiased counterpart. Moreover, we demonstrate that, as long as this relation is accounted for, the size function is a viable approach for studying cosmology with cosmic voids.

2019 ◽  
Vol 488 (3) ◽  
pp. 3526-3540 ◽  
Author(s):  
Sofia Contarini ◽  
Tommaso Ronconi ◽  
Federico Marulli ◽  
Lauro Moscardini ◽  
Alfonso Veropalumbo ◽  
...  

Abstract Cosmic voids are large underdense regions that, together with galaxy clusters, filaments and walls, build-up the large-scale structure of the Universe. The void size function provides a powerful probe to test the cosmological framework. However, to fully exploit this statistics, the void sample has to be properly cleaned from spurious objects. Furthermore, the bias of the mass tracers used to detect these regions has to be taken into account in the size function model. In our work, we test a cleaning algorithm and a new void size function model on a set of simulated dark matter halo catalogues, with different mass and redshift selections, to investigate the statistics of voids identified in a biased mass density field. We then investigate how the density field tracers’ bias affects the detected size of voids. The main result of this analysis is a new model of the size function, parametrized in terms of the linear effective bias of the tracers used, which is straightforwardly inferred from the large-scale two-point correlation function. This method is a crucial step in exploiting real surveys. The proposed size function model has been accurately calibrated on halo catalogues, and used to validate the possibility to provide forecasts on the cosmological constraints, namely on the matter density contrast, ΩM, and on the normalization of the linear matter power spectrum, σ8, at different redshifts.


2020 ◽  
Vol 500 (3) ◽  
pp. 4173-4180
Author(s):  
Stephen Stopyra ◽  
Hiranya V Peiris ◽  
Andrew Pontzen

ABSTRACT Cosmic voids provide a powerful probe of the origin and evolution of structures in the Universe because their dynamics can remain near-linear to the present day. As a result, they have the potential to connect large-scale structure at late times to early Universe physics. Existing ‘watershed’-based algorithms, however, define voids in terms of their morphological properties at low redshift. The degree to which the resulting regions exhibit linear dynamics is consequently uncertain, and there is no direct connection to their evolution from the initial density field. A recent void definition addresses these issues by considering ‘anti-haloes’. This approach consists of inverting the initial conditions of an N-body simulation to swap overdensities and underdensities. After evolving the pair of initial conditions, anti-haloes are defined by the particles within the inverted simulation that are inside haloes in the original (uninverted) simulation. In this work, we quantify the degree of non-linearity of both anti-haloes and watershed voids using the Zel’dovich approximation. We find that non-linearities are introduced by voids with radii less than $5\, \mathrm{Mpc}\, h^{-1}$, and that both anti-haloes and watershed voids can be made into highly linear sets by removing these voids.


2020 ◽  
Vol 15 (S359) ◽  
pp. 188-189
Author(s):  
Daniela Hiromi Okido ◽  
Cristina Furlanetto ◽  
Marina Trevisan ◽  
Mônica Tergolina

AbstractGalaxy groups offer an important perspective on how the large-scale structure of the Universe has formed and evolved, being great laboratories to study the impact of the environment on the evolution of galaxies. We aim to investigate the properties of a galaxy group that is gravitationally lensing HELMS18, a submillimeter galaxy at z = 2.39. We obtained multi-object spectroscopy data using Gemini-GMOS to investigate the stellar kinematics of the central galaxies, determine its members and obtain the mass, radius and the numerical density profile of this group. Our final goal is to build a complete description of this galaxy group. In this work we present an analysis of its two central galaxies: one is an active galaxy with z = 0.59852 ± 0.00007, while the other is a passive galaxy with z = 0.6027 ± 0.0002. Furthermore, the difference between the redshifts obtained using emission and absorption lines indicates an outflow of gas with velocity v = 278.0 ± 34.3 km/s relative to the galaxy.


2020 ◽  
Vol 500 (1) ◽  
pp. 911-925
Author(s):  
Carlos M Correa ◽  
Dante J Paz ◽  
Ariel G Sánchez ◽  
Andrés N Ruiz ◽  
Nelson D Padilla ◽  
...  

ABSTRACT Voids are promising cosmological probes. Nevertheless, every cosmological test based on voids must necessarily employ methods to identify them in redshift space. Therefore, redshift-space distortions (RSD) and the Alcock–Paczyński effect (AP) have an impact on the void identification process itself generating distortion patterns in observations. Using a spherical void finder, we developed a statistical and theoretical framework to describe physically the connection between the identification in real and redshift space. We found that redshift-space voids above the shot noise level have a unique real-space counterpart spanning the same region of space, they are systematically bigger and their centres are preferentially shifted along the line of sight. The expansion effect is a by-product of RSD induced by tracer dynamics at scales around the void radius, whereas the off-centring effect constitutes a different class of RSD induced at larger scales by the global dynamics of the whole region containing the void. The volume of voids is also altered by the fiducial cosmology assumed to measure distances, this is the AP change of volume. These three systematics have an impact on cosmological statistics. In this work, we focus on the void size function. We developed a theoretical framework to model these effects and tested it with a numerical simulation, recovering the statistical properties of the abundance of voids in real space. This description depends strongly on cosmology. Hence, we lay the foundations for improvements in current models of the abundance of voids in order to obtain unbiased cosmological constraints from redshift surveys.


2011 ◽  
Vol 20 (06) ◽  
pp. 1167-1169 ◽  
Author(s):  
D. L. KHOKHLOV

The results of the angular size test in the paper under comment are at variance with those for compact radio sources. The possible reason for the difference between the two results is discussed.


Traditio ◽  
2012 ◽  
Vol 67 ◽  
pp. 235-276
Author(s):  
Barbara Obrist

TheLiber de orbe, attributed to Māshā'allāh (fl. 762–ca. 815) in the list of Gerard of Cremona's translations, stands out as one of the few identifiable sources for the indirect knowledge of Peripatetic physics and cosmology at the very time Aristotle's works on natural philosophy themselves were translated into Latin, from the 1130s onward. This physics is expounded in an opening series of chapters on the bodily constitution of the universe, while the central section of the treatise covers astronomical subjects, and the remaining parts deal with meteorology and the vegetal realm. Assuming that Gerard of Cremona's translation of theLiber de orbecorresponds to the twenty-seven chapter version that circulated especially during the thirteenth and fourteenth centuries, it was, however, not this version, but a forty-chapter expansion thereof that became influential as early as the 1140s. It may have originated in Spain, as indicated, among others, by a reference to the difference of visibility of a lunar eclipse between Spain and Mecca. Unlike the twenty-seven chapterLiber de orbe, this expanded and also partly modified text remains in manuscript, and none of the three copies known so far gives a title or mentions Māshā'allāh as an author. Instead, the thirteenth-century witness that is now in New York attributes the work to an Alcantarus:Explicit liber Alcantari Caldeorum philosophi. While no Arabic original of the twenty-seven chapterLiber de orbehas come to light yet, Taro Mimura of the University of Manchester recently identified a manuscript that partly corresponds to the forty-chapter Latin text, as well as a shorter version thereof.


Problemos ◽  
2009 ◽  
Vol 76 ◽  
pp. 52-65
Author(s):  
Vytautas Rubavičius

Straipsnyje grindžiama nuomonė, jog postmodernybė yra iš modernybės kylantis kapitalizmo sistemos būvis, kuriam būdinga gyvybės suprekinimas ir suišteklinimas. Postmodernybę charakterizuoja populiariosios ir medijų kultūros išplitimas. Tos kultūros apima ne tik kultūros prekes, bet ir vartojimo būdus, įgūdžius ir jų lavinimą. Pastaruoju metu jos kuria nemirtingumo vaizdiniams bei nuojautoms palankią kultūrinę, intelektinę ir pasaulėvaizdinę terpę, kurioje struktūriškai įsitvirtina genetinis diskursas ir jo nustatomos žmogaus ir jo gyvenamo pasaulio aiškinimo gairės. Svarbus šio diskurso bruožas yra technologinis inžinerinis jo pobūdis, išryškėjęs susiejant nano ir biotechnologijas, kuriomis tikimasi įveikti gyvąją ir negyvąją gamtą skiriančią prarają, iš reikalingų atomų bei molekulių kuriant reikalingų ląstelių dalis ir klonuojant gyvas būtybes. Gyvybė suprekinama ir suišteklinama patentuojant gyvybės elementus – genus ir su jais susijusius procesus. Daroma išvada, jog visi genetikos, informatikos ir kitų mokslų laimėjimai, teikiantys žmogaus gyvenimo ilginimo galimybių, kurios palaiko gundančią nemirtingumo idėją, jau yra persmelkti prekinių santykių, tad ir pats nemirtingumas įmanomas tik kaip prekė. Aptariami kai kurie evoliuciniai ir religiniai techno sapiens sampratos aspektai. Detaliau gvildenamos dvi „nemirtingumo“ versijos: Z. Baumano, kuris nemirtingumo pažadą sieja su kompiuterinės technikos plėtra prasidėjus „Antrajai medijų erai“, ir J. Baudrillard’o, tegiančio, jog klonavimo technologijos „apgręžia“ evoliuciją ir žmogų gundo virusiniu ar vėžiniu belyčiu nemirtingumu.Pagrindiniai žodžiai: genetinis diskursas, klonavimas, medijų kultūra, nanobiotechnologijos, nemirtingumas, suprekinimas.Genetic Discourse in Media Culture: Temptation by Commodified ImmoralityVytautas Rubavičius   SummaryPostmodernity is maintained as a stage of the development of capitalism. The difference between modernity and postmodernity is explained in relation to the new sphere of commodification and resourcification, namely, that of life and of all natural living processes. Postmodern media culture, or popular culture, is peopled by signs of immortality and various kinds of immortals – cyborgs, clones, zombies, immortal human beings and others. Thus, culture accustoms a consumer to immortals and immortality which is concidered as the main goal of a human being and evolution. By nano-bio-technologies and genetic discourse this goal is made scientifically valid, thus reachable. Genetic discourse is becoming the fundamental world-view providing focal landmarks for the emerging future. Media culture supports the spreading of genetic discourse and facilitates its understanding. The temptation by immortality can be considered as a version of modernist ideology of human liberation from various natural, social and heavenly bonds. This liberation, and also secularization, is supported by a scientific genetic technological discourse which is becoming a stimulating factor of postmodern media production. The genetic explanation of the world is particularly handy for technological reflexivity: the entire world is as if encapsulated into human genes, which become the principle explaining the mystery of life, evolution and the future of humanity, thus rendering power to produce the human proper form and the future of people. All the possibilities stemming from the new genetic and biotech discoveries fell under the regulation of property relations by patenting, thus making “immortality” – as a temptation and brand – not only an exeptional commodity, but also a political tool and a commodifying force. As the relationships of private property have penetrated natural biogenetic diversity and, having turned it into a resource, the cognitive subject has reached the goal to secularise the Universe, which he has set for himself: only he as the owner and producer of genes lures people with the eternal shapes of the clones and their genetic information, which will be sustained in any location of the Universe. The temptation by “immortality” will become even stronger when the genetic code is mastered. The future of humanity is related to the mixed forms of life, trans-genic or otherwise genetically modified organisms and techno-human forms that will help to postpone, and later to conquer, death. Even thinkers with religious tendencies perceive the technological improvement of human beings as their evolution towards the techno sapiens and consider such a development as an advancement towards the Kingdom of God. The technologization of human beings is imagined in terms of their divination. Yet in this case the character of contemporary science secularising God and obliterating the perception of divinity is overlooked. Two versions of immortality are analyzed more closely – that of Z. Bauman, who links it with the development of computer technologies, and that of J. Baudrillard, who gives a warning that by cloning technologies humanity is trying to inverse the evolution and to return to the undifferentiated state of cells. The conclusion is drawn that regardless of how we understand ‘immortality,’ argue over its reality or unreality, all possibilities to prolong human life granted by genetics, informatics and other advances in science and technologies, which support the tempting idea of immortality, have already been penetrated by commodity relationships; therefore, “immortality” itself will be available only as a commodity.Keywords: cloning, commodification, genetic discourse, immortality, media culture, nano-bio-technologies.


10.29007/xqpk ◽  
2020 ◽  
Author(s):  
Van On Vo

In this paper, we investigate the linear perturbation of the material density of the universe in f(R) modified gravity of polynomial exponential form on the scale of distance below the cosmic horizon (sub-horizon). The results show that the model for the evolutionary aspects of the universe is slightly different from that in the standard cosmological model of ΛCDM. They can be used to show the difference between this modified gravitational model with the standard cosmological model of ΛCMD and other cosmological models. We also investigate the ration Ψ/ Φ and Geff / GN in the model and show that they are within allowable limits of experiments.


2017 ◽  
Vol 1 (2) ◽  
pp. 501
Author(s):  
I Gusti Ngurah Elga Ptra Sutrawan

<p><em>The philosophy of the divine NyayaDarsana and Baruch Spinoza are both a concept of the divine which gives understanding that everything comes from God. As the main cause of everything that exist and seeps into its creation which are called Atman or single substance. It confirm that in the philosophy of the divine NyayaDarsana and Baruch Spinoza contains the concept of divinity, that is Phanteism.</em></p><p><em>Based on the description, then the problem discussed in this research is : (1) How is the philosophy of the divine NyayaDarsana and Baruch Spinoza ? (2) What is the differences and equations NyayaDarsana and Baruch Spinoza ?.theory on this reseach is value theory to dissect the first problem related to the values of the philosophy of the divine which contained NyayaDarsana and the thought of Baruch Spinoza. Hermeneutic theory is used to dissect the second problem to interpret differences and equations NyayaDarsana and Baruch Baruch Spinoza. This research is a type of qualitative research with data collection techniques library study, interviews, online data and descriptive qualitative data analysis techniques, with the technique of presenting the description.</em></p><p><em>The result of this research is (1) the philosophy of the divine NyayaDarsana describe that God is the main source. Final goal all living creature that is moksa and way to reach it with knowledge of truth. The philosophy of the divine Baruch Spinoza describe that all reality comes from a single substance that is God and God immanent with nature. The ultimale goal of life based on the thought of Baruch Spinoza is to achieve happiness or freedom from the emotional shackles emotion the equation of NyayaDarsana and Baruch Spinoza is reqognize the existence of God as the main source, containing the concept of panteism. The difference is viewed from the ontology according NyayaDarsanathat the universe comes from elements of caturbhuta that together with akasa (ether) space and time, while thought of Baruch Spinoza that single substance which thought of Baruch Spinoza that single substance which called Modi, God as creator of universe, epistemology on NyayaDarsana contained about knowledge of truth to avoid from false knowledge while thought of Baruch Spinoza contain three knowledge that is the knowledge of the five senses, common sense intuitive to happiness and freedom.</em></p>


2018 ◽  
Vol 33 (28) ◽  
pp. 1850161 ◽  
Author(s):  
I. V. Fomin ◽  
S. V. Chervon

We consider the cosmological inflation with scalar–tensor gravity and compare it with standard inflation based on General Relativity. The difference is determined by the value of the parameter [Formula: see text]. This approach is associated with using the special ansatz which links a function that defines a type of gravity with a scale factor of the universe.


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