New computer simulations follow the formation of galaxies and the cosmic large-scale structure with unprecedented statistical precision

TORONTO, July 19, 2023 鈥� 91亚色 and an international team of astrophysicists have made an ambitious attempt to simulate the formation of galaxies and cosmic large-scale structure throughout staggeringly large swaths of space. First results of their 鈥淢illenniumTNG鈥� project are published in a series of 10 articles in the journal Monthly Notices of the Royal Astronomical Society. The new calculations help to subject the standard cosmological model to precision tests and to unravel the full power of upcoming new cosmological observations, say the researchers including 91亚色 Assistant Professor Rahul Kannan.

Over the past decades, cosmologists have gotten used to the perplexing conjecture that the universe鈥檚 matter content is dominated by enigmatic dark matter and that an even stranger dark energy field that acts as some kind of anti-gravity to accelerate the expansion of today鈥檚 cosmos. Ordinary baryonic matter makes up less than five per cent of the cosmic mix, but this source material forms the basis for the stars and planets of galaxies like our own Milky Way.

This seemingly strange cosmological model is known under the name LCDM. It provides a stubbornly successful description of a large number of observational data, ranging from the cosmic microwave radiation 鈥� the rest-heat left behind by the hot Big Bang 鈥� to the 鈥渃osmic web鈥�, where galaxies are arranged along an intricate network of dark matter filaments. However, the real physical nature of dark matter and dark energy is still not understood, prompting astrophysicists to search for cracks in the LCDM theory. Identifying tensions to observational data could lead to a better understanding of these fundamental puzzles about our Universe. Sensitive tests are required that need both: powerful new observational data as well as more detailed predictions about what the LCDM model actually implies.  

An international team of researchers led by the Max Planck Institute for Astrophysics (MPA) in Germany, Harvard University in the US, Durham University in the UK, and the Donostia International Physics Center in Spain, along with 91亚色, have now managed to take a decisive step forward on the latter challenge. Building up on their previous successes with the 鈥淢illennium鈥� and 鈥淚llustrisTNG鈥� projects, they developed a new suite of simulation models dubbed 鈥淢illenniumTNG鈥�, which trace the physics of cosmic structure formation with considerably higher statistical accuracy than what was possible with previous calculations.

Large simulations including new physical details

The team utilized the advanced cosmological code GADGET-4, custom-built for this purpose, to compute the largest high-resolution dark matter simulations to date, covering a region nearly 10 billion light-years across. In addition, they employed the moving-mesh hydrodynamical code AREPO to follow the processes of galaxy formation directly, throughout volumes still so large that they can be considered representative for the universe as a whole. Comparing both types of simulations allows a precise assessment of the impact of baryonic processes related to supernova explosions and supermassive black holes on the total matter distribution. An accurate knowledge of this distribution is key for interpreting upcoming observations correctly, such as so-called weak gravitational lensing effects, which respond to matter irrespective of whether it is of dark or baryonic type.

Furthermore, the team included massive neutrinos in their simulations, for the first time in simulations big enough to allow meaningful cosmological mock observations. Previous cosmological simulations had usually omitted them for simplicity, because they make up at most one to two per cent of the dark matter mass, and since their nearly relativistic velocities mostly prevent them from clumping together. Now, however, upcoming cosmological surveys (such as those of the recently launched Euclid satellite of the European Space Agency) will reach a precision allowing a detection of the associated percent-level effects. This raises the tantalizing prospect to constrain the neutrino mass itself, a profound open question in particle physics, so the stakes are high.

For their ground-breaking MillenniumTNG simulations, the researchers made efficient use of two extremely powerful supercomputers, the SuperMUC-NG machine at the Leibniz Supercomputing Center in Garching, and the Cosma8 machine at Durham Universe. More than 120聽000 compute cores toiled away for nearly two months at SuperMUC-NG, using computing time awarded by the German Gauss Centre for Supercomputing, to produce the most comprehensive hydrodynamical simulation model to date. MillenniumTNG is tracking the formation of about one hundred million galaxies in a region of the universe around 2400 million light-years across (see Figure 1). This calculation is about 15 times bigger than the previously best is this category, the TNG300 model of the IllustrisTNG project.

Using Cosma8, the team computed an even bigger volume of the universe, filled with more than a trillion dark matter particles and more than 10 billion particles for tracking massive neutrinos (see Figure 2). Even though this simulation did not follow the baryonic matter directly, its galaxy content can be accurately predicted in MillenniumTNG with a semi-analytic model that is calibrated against the full physical calculation of the project. This procedure leads to a detailed distribution of galaxies and matter in a volume that for the first time is large enough to be representative for the universe as a whole, putting comparisons to upcoming observational surveys on a sound statistical basis.

Theoretical predictions for cosmology

The first results of the MillenniumTNG project show a wealth of new theoretical predictions that reinforce the importance of computer simulations in modern cosmology. The team has written and submitted ten introductory scientific papers for the project. Eight of them have just appeared simultaneously in the journal MNRAS, the remaining two are about to follow shortly.

One timely study examines the discovery of a population of very massive galaxies in the young universe with the James Webb Space Telescope. The masses of these galaxies are unexpectedly large just a brief time after the Big Bang, seemingly defying theoretical expectations. Dr. Kannan analyzed the predictions of MillenniumTNG for this early epoch. While the simulations agree with the observations out to redshifts of z=10 (when the universe was less than 500 million years old), he confirmed that, if they hold up, the new results by JWST at even higher redshift conflicts with the simulation predictions.

鈥淧erhaps star formation is much more efficient shortly after the Big Bang than at later times, or maybe massive stars are formed in higher proportions back then, making these galaxies unusually bright鈥�, says Kannan of 91亚色鈥檚 Faculty of Science.

Another study looked at the shapes of galaxies. Nearby galaxies have the subtle tendency to orient their shapes in similar directions instead of pointing randomly, an effect called 鈥渋ntrinsic galaxy alignments鈥�. This poorly understood effect distorts inferences based on weak gravitational lensing, which creates its own statistical alignment signal. The MillenniumTNG project could for the first-time measure intrinsic alignments with very high signal-to-noise directly from the shapes of the simulated galaxies, out to distances of several hundred million light-years. 鈥淧erhaps our determination of the intrinsic alignment of galaxy orientations can help to resolve the current discrepancy between the amplitude of matter clustering inferred from weak lensing and from the cosmic microwave background,鈥� says PhD-student Ana Maria Delgado of Harvard University, first author of this study of the MillenniumTNG team. Using these results, astronomers will be able to correct for this important systematic effect much better.

Other works of the team鈥檚 initial analysis focus on the clustering signals of galaxies. For example, MPA PhD student Monica Barrera produced extremely large and highly realistic mock catalogues of galaxies on the past backwards 鈥渓ightcone鈥� of a fiducial observer (see Figure 3). In this case, galaxies that are more distant are also automatically younger, reflecting the travel time of the light that is reaching our telescopes. Using these virtual observations, she looked at the so-called baryonic acoustic oscillation (BAO) feature (which provides a cosmologically important standard ruler) in the projected two-point correlation function of galaxies. Her results showed, that measuring these BAOs is a fairly tricky endeavour that can be significantly influenced by so-called cosmic variance effects 鈥� even when extremely large volumes are studied in observational surveys. While in simulations one can observe the modelled universe from different vantage points to recover the correct statistical ensemble average, this is unfortunately not readily possible for the real Universe. 鈥淭he MillenniumTNG simulations are so big and contain so many galaxies, more than 1 billion in the biggest calculation, that it was really hard to study them鈥�, says Monica Barrera. 鈥淎nalysis scripts that work just fine for smaller simulations tend to take forever for MillenniumTNG.鈥�      

Analyzing cosmological data

The flurry of first results from the MillenniumTNG simulations make it clear that they will be of great help to design better strategies for the analysis of upcoming cosmological data. The team鈥檚 principal investigator, Professor Volker Springel from MPA argues that 鈥淢illenniumTNG combines recent advances in simulating galaxy formation with the field of cosmic large-scale structure, allowing an improved theoretical modelling of the connection of galaxies to the dark matter backbone of the Universe. This may well prove instrumental for progress on key questions in cosmology, such as how the mass of neutrinos can be best constrained with large-scale structure data.鈥� The MillenniumTNG simulations produced more than three Petabytes of simulation data, forming a rich asset for further research that will keep the participating scientists busy for many years to come.

Original scientific publications:

• The MillenniumTNG Project: The galaxy population at z 鈮� 8
  R. Kannan, V. Springel, L. Hernquist, R. Pakmor, A. M. Delgado, B. Hadzhiyska, C. Hern谩ndez-Aguayo, M. Barrera, F. Ferlito, S. Bose, S. D. M. White, C. Frenk, A. Smith, E. Garaldi
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: High-precision predictions for matter clustering and halo statistics
  C. Hern谩ndez-Aguayo, V. Springel, R. Pakmor, M. Barrera, F. Ferlito, S. D. M. White, L. Hernquist, B. Hadzhiyska, A. M. Delgado, R. Kannan, S. Bose, C. Frenk
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: The hydrodynamical full physics simulation and a first look at its galaxy clusters
  R. Pakmor, V. Springel, J. P. Coles, T. Guillet, C. Pfrommer, S. Bose, M. Barrera, A. M. Delgado, F. Ferlito, C. Frenk, B. Hadzhiyska, C. Hern谩ndez-Aguayo, L. Hernquist, R. Kannan, S. D. M. White
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: Semi-analytic galaxy formation models on the past lightcone
  M. Barrera, V. Springel, S. White, C. Hern谩ndez-Aguayo, L. Hernquist, C. Frenk, R. Pakmor, F. Ferlito, B. Hadzhiyska, A. M. Delgado, R. Kannan, S. Bose
  MNRAS, submitted (preprint: )
• The MillenniumTNG Project: Refining the one-halo model of red and blue galaxies at different redshifts
  B. Hadzhiyska, L. Hernquist, D. Eisenstein, A. M. Delgado, S. Bose, R. Kannan, R. Pakmor, V. Springel, S. Contreras, M. Barrera, F. Ferlito, C. Hern谩ndez-Aguayo, S. D. M. White, C. Frenk
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: An improved two-halo model for the galaxy-halo connection of red and blue galaxies
  B. Hadzhiyska, D. Eisenstein, L. Hernquist, R. Pakmor, S. Bose, A. M. Delgado, S. Contreras, R. Kannan, S. D. M. White, V. Springel, C. Frenk, C. Hern谩ndez-Aguayo, F. Ferlito, M. Barrera
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: The large-scale clustering of galaxies
  S. Bose, B. Hadzhiyska, M. Barrera, A. M. Delgado, F. Ferlito, C. Frenk, C. Hern谩ndez-Aguayo, L. Hernquist, R. Kannan, R. Pakmor, V. Springel, S. D. M. White
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: Inferring cosmology from galaxy clustering with accelerated N-body scaling and subhalo abundance matching
  S. Contreras, R. E. Angulo, V. Springel, S. D. M. White, B. Hadzhiyska, L. Hernquist, R. Pakmor, R. Kannan, C. Hern谩ndez-Aguayo, M. Barrera, F. Ferlito, A. M. Delgado, S. Bose, C. Frenk
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: Intrinsic alignments of galaxies and halos
  A. M. Delgado, B. Hadzhiyska, S. Bose, V. Springel, L. Hernquist, M. Barrera, R. Pakmor, F. Ferlito, R. Kannan, C. Hern谩ndez-Aguayo, S. D. M. White, C. Frenk
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: The impact of baryons and massive neutrinos on high-resolution weak gravitational lensing convergence maps
  F. Ferlito, V. Springel, C. T. Davies, C. Hern谩ndez-Aguayo, R. Pakmor, M. Barrera, S. D. M. White, A. M. Delgado, B. Hadzhiyska, L. Hernquist, R. Kannan, S. Bose, C. Frenk
  MNRAS, submitted (preprint: )

Further Links:

Web site of the MillenniumTNG project

Gauss Centre for Supercomputing

SuperMUC-NG at the Leibniz Supercomputing Centre

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91亚色 is a modern, multi-campus, urban university located in Toronto, Ontario. Backed by a diverse group of students, faculty, staff, alumni and partners, we bring a uniquely global perspective to help solve societal challenges, drive positive change and prepare our students for success. 91亚色's fully bilingual Glendon Campus is home to Southern Ontario's Centre of Excellence for French Language and Bilingual Postsecondary Education. 91亚色鈥檚 campuses in Costa Rica and India offer students exceptional transnational learning opportunities and innovative programs. Together, we can make things right for our communities, our planet, and our future.

Media Contacts

91亚色: Sandra McLean, 91亚色 Media Relations, 416-272-6317, sandramc@yorku.ca

MPA: Hannelore H盲mmerle, +49-89-30000-3980, pr@mpa-garching.mpg.de

Harvard & Smithsonian Center for Astrophysics: +1- 617-721-7371, pr@, https://cfa.harvard.edu

Communications Office contact Durham University: Leighton Kitson, communications.team@durham.ac.uk,

Scientific contact:

Prof. Dr. Volker Springel, Max-Planck Institute for Astrophysics (MPA), +49-89-30000-2195, vspringel@mpa-garching.mpg.de

Figures / Captions:

Figure 1: /news/wp-content/uploads/sites/242/2023/07/figure1-1-scaled.jpg

Projections of gas (top left), dark matter (top right), and stellar light (bottom center) for a slice in the largest hydrodynamical simulation of MillenniumTNG at the present epoch. The slice is about 35 million light-years thick. The projections show the vast physical scales in the simulation from size, about 2400 million light-years across, to an individual spiral galaxy (final round inset) with a radius of ~150 000 light-years. The underlying calculation is presently the largest high-resolution hydrodynamical simulation of galaxy formation, containing more than 160 billion resolution elements. 漏 MPA

Figure 2: /news/wp-content/uploads/sites/242/2023/07/Figure-2.jpg

Comparison of the neutrino (top) and dark matter (bottom) distributions on the past backwards lightcone of a fiducial observer positioned at the centre of the two horizontal stripes. As cosmic expansion slows down the neutrinos at late times (small redshift/distance), they start to weakly cluster around the biggest concentrations of dark matter as shown by a comparison of the zoomed insets. This slightly increases the mass and further growth rate of these largest structures. 漏 MPA

Figure 3: /news/wp-content/uploads/sites/242/2023/07/Figure-3-scaled.jpg

Galaxy distribution on the past backwards lightcone in MillenniumTNG, where the galaxies are predicted with a sophisticated semi-analytic model on top of the dark matter backbone. Galaxies are shown down to Johnson apparent magnitude 饾憛 < 23, in a 180 degrees wide, thin wedge with opening angle 0.24 degrees, out to redshift 饾懅 = 2. The galaxy positions are drawn as circles with comoving coordinates in real space, using red for galaxies with rest frame color index 饾惖鈭掟潙� > 0.7, and blue otherwise. Real observations of the galaxy positions would additionally be perturbed by small shifts along the line of sight due to the Doppler effects from the galaxies鈥� motions, an effect that can also be easily included in the models. The two circular insets show nested zooms with diameters of around 1.25 billion light-years and 125 million light-years, and fainter apparent magnitude limits of 饾憛 < 25 and 饾憛 < 28, respectively. 漏 MPA

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TORONTO, Sept. 29, 2022 鈥� Using the James Webb Space Telescope (JWST), researchers from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS) team, including 91亚色, have identified the most distant globular clusters ever discovered. These dense groups of millions of stars may be relics that contain the first and oldest stars in the universe.

The early analysis of Webb鈥檚 First Deep Field image, which depicts some of the universe鈥檚 earliest galaxies, is published today in .

鈥淕lobular clusters are quite mysterious. They orbit the Milky Way and other galaxies, however, we have little idea where they come from,鈥� says study co-author Associate Professor Adam Muzzin of 91亚色鈥檚 Faculty of Science. 鈥淲ith the James Webb Space Telescope, we were able to see incredibly far into the past, much farther than we鈥檝e ever been able to see before 鈥� and what we saw was spectacular.鈥�

91亚色 PhD student Ghassan Sarrouh, also a co-author on the research, says 鈥淚n this case, we were able to identify several globular clusters, collections of ancient stars, far beyond our Milky Way some nine billion light years away when the universe was about a third of its current age. It鈥檚 a really exciting and significant finding.鈥�

The research team looked at one galaxy in particular to understand what was happening around it.

鈥淛WST was built to find the first stars and the first galaxies and to help us understand the origins of complexity in the universe, such as the chemical elements and the building blocks of life,鈥� says Lamiya Mowla, Dunlap Fellow at the Dunlap Institute for Astronomy & Astrophysics at the University of Toronto and co-lead author of the study. 鈥淭his discovery in Webb鈥檚 First Deep Field is already providing a detailed look at the earliest phase of star formation, confirming the incredible power of JWST.鈥�

In the finely detailed Webb鈥檚 First Deep Field image, the researchers zeroed in on what they鈥檝e dubbed 鈥渢he Sparkler galaxy,鈥� which is nine billion light years away. This galaxy got its name for the compact objects appearing as small yellow-red dots surrounding it, referred to by the researchers as 鈥渟parkles.鈥� The team posited that these sparkles could either be young clusters actively forming stars 鈥� born three billion years after the Big Bang at the peak of star formation 鈥� or old globular clusters. Globular clusters are ancient collections of stars from a galaxy鈥檚 infancy and contain clues about its earliest phases of formation and growth.

From their initial analysis of 12 of these compact objects, the researchers determined that five of them are not only globular clusters but among the oldest ones known.

鈥淟ooking at the first images from JWST and discovering old globular clusters around distant galaxies was an incredible moment, one that wasn鈥檛 possible with previous Hubble Space Telescope imaging,鈥� says Kartheik G. Iyer, Dunlap Fellow at the Dunlap Institute for Astronomy & Astrophysics at the University of Toronto and co-lead author of the study. 鈥淪ince we could observe the sparkles across a range of wavelengths, we could model them and better understand their physical properties, like how old they are and how many stars they contain. We hope the knowledge that globular clusters can be observed at from such great distances with JWST will spur further science and searches for similar objects.鈥�

The Milky Way galaxy has about 150 globular clusters, and how and when exactly these dense clumps of stars formed is not well understood. Astronomers know that globular clusters can be extremely old, but it is incredibly challenging to measure their ages. Using very distant globular clusters to age-date the first stars in distant galaxies has not been done before and is only possible with JWST.

Until now, astronomers could not see the surrounding compact objects of the Sparkler galaxy with the Hubble Space Telescope (HST). This changed with JWST's increased resolution and sensitivity, unveiling the tiny dots surrounding the galaxy for the first time in Webb鈥檚 First Deep Field image. The Sparkler galaxy is special because it is magnified by a factor of 100 due to an effect called gravitational lensing 鈥� where the SMACS 0723 galaxy cluster in the foreground distorts what is behind it, much like a giant magnifying glass. Moreover, gravitational lensing produces three separate images of the Sparkler, allowing astronomers to study the galaxy in greater detail.

鈥淥ur study of the Sparkler highlights the tremendous power in combining the unique capabilities of JWST with the natural magnification afforded by gravitational lensing,鈥� says CANUCS team lead Chris Willott from the National Research Council鈥檚 Herzberg Astronomy and Astrophysics Research Centre. 鈥淭he team is excited about more discoveries to come when JWST turns its eye on the CANUCS galaxy clusters next month.鈥�

The researchers combined new data from JWST鈥檚 Near-Infrared Camera (NIRCam) with HST archival data. NIRCam detects faint objects using longer and redder wavelengths to observe past what is visible to the human eye and even HST. Both magnifications due to the lensing by the galaxy cluster and the high resolution of JWST are what made observing compact objects possible.

The Canadian-made Near-Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST provided independent confirmation that the objects are old globular clusters because the researchers did not observe oxygen emission lines 鈥� emissions with measurable spectra given off by young clusters that are actively forming stars. NIRISS also helped unravel the geometry of the triply lensed images of the Sparkler.

JWST will observe the CANUCS fields starting in October 2022, leveraging JWST data to examine five massive clusters of galaxies, around which the researchers expect to find more such systems. Future studies will also model the galaxy cluster to understand the lensing effect and execute more robust analyses to explain the star formation histories.

Collaborating institutions include Saint Mary鈥檚 University and institutions in the United States and Europe. The research was supported by the Canadian Space Agency and the Natural Sciences and Engineering Research Council of Canada.

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91亚色 is a modern, multi-campus, urban university located in Toronto, Ontario. Backed by a diverse group of students, faculty, staff, alumni and partners, we bring a uniquely global perspective to help solve societal challenges, drive positive change and prepare our students for success. 91亚色's fully bilingual Glendon Campus is home to Southern Ontario's Centre of Excellence for French Language and Bilingual Postsecondary Education. 91亚色鈥檚 campuses in Costa Rica and India offer students exceptional transnational learning opportunities and innovative programs. Together, we can make things right for our communities, our planet, and our future.

Media Contact:

Sandra McLean, 91亚色 Media Relations, 416-272-6317, sandramc@yorku.ca

The post Webb reveals a galaxy sparkling with the universe鈥檚 oldest star clusters appeared first on News@91亚色.

Modelling shows big galaxies get bigger by merging with smaller ones

TORONTO, Friday, April 24, 2020 鈥� Galaxies grow large by eating their smaller neighbours, finds an international research team, including 91亚色.

Exactly how massive galaxies attain their size is poorly understood, not least because they swell over billions of years. But now through a combination of observation and modelling, researchers, including the Faculty of Science鈥檚 Leo Alcorn, a 91亚色 Science Fellow, have found a clue.

Distribution of dark matter density overlayed with the gas density. This image cleanly shows the gas channels connecting the central galaxy with its neighbours. Credit: Gupta et al/ASTRO 3D

The research team, led by Post-Doctoral Researcher Anshu Gupta from Australia鈥檚 ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), included scientists from Australian, the United States, Canada, Mexico, Belgium and the Netherlands. They ran their modelling on a specially designed set of simulations known as IllustrisTNG.

In the paper, , published in , the scientists combine data from an Australian project called the Multi-Object Spectroscopic Emission Line (MOSEL)聽survey with a cosmological modelling program running on some of the world鈥檚 largest supercomputers to glimpse the forces that create these ancient galactic monsters.

By analysing how gases within galaxies move it is possible to discover the proportion of stars made internally 鈥� and the proportion effectively cannibalised from elsewhere.

鈥淲e found that distant, massive galaxies, about 10 billion light years away from us, have more chaotic or random internal motions,鈥� says Alcorn. 鈥淭his is likely because these galaxies have merged with smaller galaxies, producing gravitational disruptions to the orbits of stars and gas. This matter is incorporated into the massive galaxies, growing the galaxy in mass and size鈥�

Because light takes time to travel through the universe, galaxies further away from the Milky Way are seen at an earlier point in their existence. The team found that observation and modelling of these very distant galaxies revealed much less variation in their internal movements.

鈥淎s these huge galaxies gain more stars, they are able to gravitationally attract and merge with more surrounding small galaxies. Over billions of years, these old, massive galaxies grow increasingly chaotic, disordered, and large, constantly feeding on nearby neighbours,鈥� says Alcorn.

This is a multi-year, international project that aims to build a series of large cosmological models of how galaxies form. The program is so big that it has to run simultaneously on several of the world鈥檚 most powerful supercomputers.

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91亚色 champions new ways of thinking that drive teaching and research excellence. Our students receive the education they need to create big ideas that make an impact on the world. Meaningful and sometimes unexpected careers result from cross-disciplinary programming, innovative course design and diverse experiential learning opportunities. 91亚色 students and graduates push limits, achieve goals and find solutions to the world鈥檚 most pressing social challenges, empowered by a strong community that opens minds. 91亚色 U is an internationally recognized research university 鈥� our 11 faculties and 25 research centres have partnerships with 200+ leading universities worldwide. Located in Toronto, 91亚色 is the third largest university in Canada, with a strong community of 53,000 students, 7,000 faculty and administrative staff, and more than 300,000 alumni. 91亚色 U's fully bilingual Glendon Campus is home to Southern Ontario's Centre of Excellence for French Language and Bilingual Postsecondary Education.

Media Contact:

Sandra McLean, 91亚色 Media Relations, 416-272-6317, sandramc@yorku.ca

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