Understanding the cosmic web: Unveiling the evolution of cosmic filaments with the MillenniumTNG simulation

Artist’s representation of the density field and cosmic web structures, in analogy with a mountain. Gray points illustrate galaxies as tracers of the cosmic web. Credit: Daniela Galárraga-Espinosa/MPA

Distribution of different matter components revealing the web-like structure of the large-scales of the Universe, the Cosmic Web (simulated image). Credit: Daniela Galárraga-Espinosa/MPA

Slices of the MilleniumTNG simulation showing the galaxy distribution (top) and the associated filaments (bottom) at different cosmic times. Credit: Daniela Galárraga-Espinosa/MPA

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A careful analysis of the filaments in the cosmic large-scale structure has revealed interesting new findings about the evolution and complexities of the cosmic web. While some filaments show a significant evolution – depending on their cosmic environment – global filament properties are preserved, which could be used in future cosmological studies. The MPA team also developed a new method to allow for rigorous calibration of the filament catalogues.

What are cosmic filaments?

In the 1980s, observations of galaxies in regions like the Perseus cluster, the Coma/A1367 supercluster, and the Center for Astrophysics galaxy survey unveiled a fascinating discovery: the universe is structured like a complex network, called the cosmic web. This structure is made of nodes, filaments, walls, and vast voids, intricately woven together. Dark matter and gas, influenced by gravity’s pull, sculpt this cosmic architecture, with galaxies serving as markers tracing its features. Since its discovery, the cosmic web has been meticulously mapped by numerous galaxy surveys, each providing unique insights into the structure of the cosmos.

While the dense clusters of galaxies, or nodes, have been thoroughly studied, the less dense and more intricate cosmic filaments remain less understood. Their faint signals make them difficult to observe, as research shows that dark matter density in these filaments is significantly lower than in clusters, complicating their detection in galaxy surveys.

Despite these challenges, cosmological simulations suggest that cosmic filaments contain over 50% of the universe’s matter. Understanding these structures is therefore essential for a comprehensive view of the universe, and to know how galaxies form and evolve within this large interconnected web.

New insights from the MillenniumTNG simulation

In this study, MPA researcher Daniela Galárraga-Espinosa, in collaboration with local and international colleagues, has utilized the new state-of-the-art numerical simulation, MillenniumTNG, to delve into the intricate structure of the cosmic web across different epochs of the universe. The hydro-dynamical runs at various redshifts (z = 0, 1, 2, 3, and 4) led to meticulously constructed catalogues of cosmic filaments. This backbone of the cosmic web could then be studied in terms of spatial evolution over cosmic time, as well as lengths, growth rates, and radial density profiles, providing unprecedented insights into the evolution and diversity of these cosmic structures:

1. Unveiling global properties of filament across time: Through careful analysis, the study showed that the filament lengths and density profiles across varying cosmic epochs are remarkably stable. The global population of cosmic filaments shows only minimal evolution over a span of approximately 12.25 billion years.

2. Tracking individual filaments: For the first time, the study has associated a large number of filaments across different redshifts, following the evolution of individual structures across time. While some filaments can significantly contract or elongate with time, the global filament properties are preserved. The team therefore plans to use fundamental filament properties for cosmological analyses in the next study.

3. Understanding cosmic filament diversity: The study also highlights the differences between filament populations at a specific time. At all redshifts, the longest filaments exceed 100 megaparsecs, two orders of magnitude longer than the shortest ones. In addition, these extreme-length filaments have very distinct density profiles. Complementing previous research, the study indicates that environmental factors could drive this diversity: filaments in high-density regions collapse and shorten over time, while those near cosmic voids expand as the cosmic web stretches.

4. Towards more robust filament catalogues: The team developed a method anchored in physical principles to allow for rigorous calibration and testing of the identified cosmic skeletons. This methodology will hopefully inspire future investigations to adopt similar robust approaches, fostering a more unified understanding of cosmic filament detection techniques within the scientific community.

These discoveries represent major advancements in our understanding of the Universe’s large-scale structure and open new avenues for exploring the complexities of the cosmic web.

Source: Max Planck Institute for Astrophysics

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Author:

Daniela Galarraga-Espinosa
Postdoc
tel:2269
danigaes@mpa-garching.mpg.de

Original publication

D. Galárraga-Espinosa et al.
Evolution of cosmic filaments in the MTNG simulation
Astronomy & Astrophysics, Volume 684, id.A63, 17 pp.
Source | DOI

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The Cosmic Evolution of Galaxies

A snapshot from the Illustris Project computer simulation of cosmic structure formation. This artificially colored image shows filaments and galaxies in the web of cosmic matter, as seen today over a field-of-view about fifty million light-years across. A new paper examines the changing frequency of galaxy collisions, as computed by in Illustris, as the universe evolves from the big bang to the present day.Credit:   The Illustris Project

Our knowledge of the big bang has increased dramatically in the past decade, as satellites and ground-based studies of the cosmic microwave background have refined parameters associated with the very early universe, achieving amazing precisions (though not necessarily accuracies) of a few percent. Unfortunately, our knowledge of what happened after that - from those first few hundred thousand years until today, 13.7 billion years later - is very much a work-in-progress. We know that galaxies and their stars formed out of the cooling, filamentary network of matter from that early era. They re-ionized the hydrogen gas, and then continued to evolve, and collide with one another as the universe steadily expanded. Distant galaxies are faint and hard to detect, however, and although observations have made excellent progress in piecing together the story line, astronomers have turned to theory and computer simulations to try to complete the picture.

There are three main theoretical approaches to study the cosmic frequency of galaxy mergers, which differ in how they model galaxies. The first approach does not attempt to model galaxy formation from first principles, and instead "paints" galaxies onto the dark matter environment (they are called "halos") according to constraints set by observations. The second approach models galaxy formation by means of simple mathematical recipes, again using dark matter halos as the backbone of the model. The third method, hydrodynamic simulations, attempts to model everything (dark matter, gas and stars) self-consistently, a task that until recently had been computationally too difficult.

CfA astronomers Vicente Rodriguez-Gomez, Shy Genel, Annalisa Pillepich, Dylan Nelson, and Lars Hernquist and their colleagues have developed a new theoretical framework for calculating the frequency of galaxy mergers in the Illustris Project, a cosmological hydrodynamic simulation which models the formation of galaxies in cosmic volumes about three hundred million light-years in size, huge enough to replicate many known properties of galaxies and clusters both locally and at earlier epochs. The large volume, the self-consistent treatment of normal matter, and the realistic galaxy formation model used, allows the Illustris simulation to provide an unprecedented and precise study of mergers over cosmic time.

The astronomers find clear evidence for steadily decreasing galaxy merger rates (the merger frequency three billion years after the big bang was about fifteen times higher than it is today), and they clarify the nature of mergers, for example, finding the most useful definition for the mass ratio of the merging galaxies and constraining the epoch of mass infall during a collision. They report some sharp differences between their results and those predicted by some other popular theories, as well as some ambiguities in the (still imprecise) observed datasets. Their important research marks the start of a more detailed series of investigations into the cosmic evolution of galaxies.

Reference(s): 

"The Merger Rate of Galaxies in the Illustris Simulation: A Comparison with Observations and Semi-empirical Models," Vicente Rodriguez-Gomez, Shy Genel, Mark Vogelsberger, Debora Sijacki, Annalisa Pillepich, Laura V. Sales, Paul Torrey, Greg Snyder, Dylan Nelson, Volker Springel, Chung-Pei Ma, and Lars Hernquist, MNRAS, 449, 49, 2015

Source: Smithsonian Astrophysical Observatory

It’s Filamentary: How Galaxies Evolve in the Cosmic Web

Galaxies are distributed along a cosmic web in the universe. “Mpc/h” is a unit of galactic distance (1 Mpc/h is more than 3.2 million light-years)

Image credit: Volker Springel, Virgo Consortium

Behnam Darvish (left) and Bahram Mobasher are astronomers in the Department of Physics and Astronomy at UC Riverside

Photo credit: UC Riverside

UC Riverside-led team proposes that filaments in the cosmic web played a critical role in the distant universe

RIVERSIDE, Calif. – How do galaxies like our Milky Way form, and just how do they evolve?  Are galaxies affected by their surrounding environment? An international team of researchers, led by astronomers at the University of California, Riverside, proposes some answers.

The researchers highlight the role of the “cosmic web” – a large-scale web-like structure comprised of galaxies – on the evolution of galaxies that took place in the distant universe, a few billion years after the Big Bang.  In their paper, published Nov. 20 in the Astrophysical Journal, they present observations showing that thread-like “filaments” in the cosmic web played an important role in this evolution.

“We think the cosmic web, dominated by dark matter, formed very early in the history of the universe, starting with small initial fluctuations in the primordial universe,” said Behnam Darvish, a Ph.D. graduate student in the Department of Physics and Astronomy at UC Riverside, who led the research project and is the first author on the paper.  “Such a ‘skeletal’ universe must have played, in principle, a role in galaxy formation and evolution, but this was incredibly hard to study and understand until recently.”

The distribution of galaxies and matter in the universe is non-random.  Galaxies are organized, even today, in a manner resembling an enormous network – the cosmic web.  This web has dense regions made up of galaxy clusters and groups, sparsely populated regions devoid of galaxies, as well as the filaments that link overdense regions.

“The filaments are like bridges connecting the denser regions in the cosmic web,” Darvish explained.  “Imagine threads woven into the web.”

Videos showing structures in the cosmic web:

• http://www.mpa-garching.mpg.de/galform/data_vis/millennium_sim_1024x768.avi [Credit: Springel et al. (Virgo Consortium)]
• http://vimeo.com/36095013 [Credit: Miguel Aragon-Calvo]
• http://www.mpa-garching.mpg.de/galform/data_vis/g696_mpeg4.avi  [Credit: Klaus Dolag]
• http://www.mpa-garching.mpg.de/galform/data_vis/g696_fast_mpeg4.avi [Credit: Klaus Dolag]

It is well known in astronomy that galaxies residing in less dense regions have higher probability of actively forming stars (much like our Milky Way), while galaxies in denser regions form stars at a much lower rate.

“But the role of intermediate environments and, in particular, the role of filaments and the cosmic web in the early universe remained, until very recently, a mystery,” said coauthor Bahram Mobasher, a professor of physics and astronomy at UCR and Darvish’s adviser.

What greatly assisted the researchers is a giant section of the cosmic web first revealed in two big cosmological surveys (COSMOS and HiZELS).  They proceeded to explore data also from several telescopes (Hubble, VLT, UKIRT and Subaru).  They then applied a new computational method to identify the filaments, which, in turn, helped them study the role of the cosmic web.

They found that galaxies residing in the cosmic web/filaments have a much higher chance of actively forming stars.  In other words, in the distant universe, galaxy evolution seems to have been accelerated in the filaments.

“It is possible that such filaments ‘pre-process’ galaxies, accelerating their evolution while also funneling them towards clusters, where they are fully processed by the dense environment of clusters and likely end up as dead galaxies,” Darvish said.  “Our results also show that such enhancement/acceleration is likely due to galaxy-galaxy interactions in the filaments.”

Because of the complexities involved in quantifying the cosmic web, astronomers usually limit the study of the cosmic web to numerical simulations and observations in our local universe. However, in this new study, the researchers focused their work on the distant universe – when the universe was approximately half its present age.

“We were surprised by the crucial role the filaments play in galaxy formation and evolution,” Mobasher said.  “Star formation is enhanced in them.  The filaments likely increase the chance of gravitational interaction between galaxies, which, in turn, results in this star-formation enhancement. There is evidence in our local universe that this process in filaments also continues to occur at the present time.”

Darvish and Mobasher were joined in this research by L. V. Sales at UCR; David Sobral at the Universidade de Lisboa, Portugal; N. Z. Scoville at the California Institute of Technology; P. Best at the Royal Observatory of Ediburgh, United Kingdom; and I. Smail at Durham University, United Kingdom.

Next, the team plans to extend this study to other epochs in the age of the universe to study the role of the cosmic web/filaments in galaxy formation and evolution across cosmic time.

“This will be a fundamental piece of the puzzle in order to understand how galaxies form and evolve as a whole,” Sobral said.

The UCR researchers were supported in the study by a grant to Mobasher from NASA through the Space Telescope Science Institute.

Media Contact

Iqbal Pittalwala
Tel: (951) 827-6050
E-mail: iqbal@ucr.edu
Twitter: UCR_Sciencenews
 

Additional Contacts  

Behnam Darvish
E-mail: bdarv001@ucr.edu
 
Bahram Mobasher
Tel: 951 827 7190
E-mail: mobasher@ucr.edu

Related Links

• Department of Physics and Astronomy
• Research paper

Source: University of California - Riverside - USR Today

Using artificial intelligence to chart the universe

Supergalactic plot of the Cosmic Web Structure

A slice through the three dimensional Local Universe with side 370 Million light years is shown. The red circles represent observed galaxies from the 2MRS survey. The blue circles are random galaxies filled in the so-called zone of avoidance, where the stars of our Milky Way do not permit us to observe extragalactic sources. The light and dark colour code stands for the density field reconstruction using the KIGEN artificial intelligence code showing the cosmic web matching the distribution of galaxies. Image #1

Sky plot of the Comic Web Structure

The projected density field on the sky up to distances of  about 185 Million light years distance obtained by the KIGEN code from the 2MRS data is shown. Image #2

Astronomers in Germany have developed an artificial intelligence algorithm to help them chart and explain the structure and dynamics of the universe around us. The team, led by Francisco Kitaura of the Leibniz Institute for Astrophysics in Potsdam, report their results in the journal Monthly Notices of the Royal Astronomical Society.

Scientists routinely use large telescopes to scan the sky, mapping the coordinates and estimating the distances of hundreds of thousands of galaxies and so enabling scientists to map the large-scale structure of the Universe. But the distribution they see is intriguing and hard to explain, with galaxies forming a complex ‘cosmic web’ showing clusters, filaments connecting them, and large empty regions in between.

The driving force for such a rich structure is gravitation. Around 5 percent of the cosmos appears to be made of ‘normal’ matter that makes up the stars, planets, dust and gas we can see and around 23 percent is made up of invisible ‘dark’ matter. The largest component, some 72 percent of the cosmos, is made up of a mysterious ‘dark energy’ thought to be responsible for accelerating the expansion of the Universe. This Lambda Cold Dark Matter (LCDM) model for the universe was the starting point for the work of the Potsdam team.

Measurements of the residual heat from the Big Bang – the so-called Cosmic Microwave Background Radiation or CMBR – allow astronomers to determine the motion of the Local Group, the cluster of galaxies that includes the Milky Way, the galaxy we live in. Astronomers try to reconcile this motion with that predicted by the distribution of matter around us, but this is compromised by the difficulty of mapping the dark matter in the same region.

“Finding the dark matter distribution corresponding to a galaxy catalogue is like trying to make a geographical map of Europe from a satellite image during the night which only shows the light coming from dense populated areas”, says Dr Kitaura.

His new algorithm is based on artificial intelligence (AI). It starts with the fluctuations in the density of the universe seen in the CMBR, then models the way that matter collapses into today’s galaxies over the subsequent 13700 million years. The results of the AI algorithm are a close fit to the observed distribution and motion of galaxies.

Dr Kitaura comments, “Our precise calculations show that the direction of motion and 80 percent of the speed of the galaxies that make up the Local Group can be explained by the gravitational forces that arise from matter up to 370 million light years away. In comparison the Andromeda Galaxy, the largest member of the Local Group, is a mere 2.5 million light years distant so we are seeing how the distribution of matter at great distances affects galaxies much closer to home.

Our results are also in close agreement with the predictions of the LCDM model. To explain the rest of the 20 percent of the speed, we need to consider the influence of matter up to about 460 million light years away, but at the moment the data are less reliable at such a large distance.

Despite this caveat, our model is a big step forward. With the help of AI, we can now model the universe around us with unprecedented accuracy and study how the largest structures in the cosmos came into being.”

Since 2011 Francisco Kitaura has been working at the AIP. His publication is available online on http://arxiv.org/abs/1205.5560 and will soon be published in Monthly Notices of the Royal Astronomical Society (MNRAS).

Science contact:

Dr. Francisco-Shu Kitaura, +49 331-7499 447, fkitaura@aip.de

Research, Images, Movies: http://www.aip.de/Members/fkitaura

Press contact:

Dr. Gabriele Schönherr / Kerstin Mork, +49 331-7499 469, presse@aip.de

The key topics of the Leibniz Institute for Astrophysics are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. Since 1992 the AIP is a member of the Leibniz Association.

Source: Leibniz Institute for Astrophysics