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ROMFORSK-Program for romforskning

Simulating the Circumgalactic Medium and the Cycle of Baryons In and Out of Galaxies Throughout Cosmic History

Alternative title: Simulering av det sirkumgalaktiske medium og baryonsykelen inn og ut av galakser gjennom universets historie

Awarded: NOK 7.8 mill.

Project Number:


Project Period:

2018 - 2023

Funding received from:


How galaxies form and evolve throughout cosmic history is a central question of modern cosmology. Galaxies are not isolated objects in the Universe, but fundamentally connected within a “cosmic web”. This "web" is scaffolded by gravitational collapse of dark matter into sheets and filamentary structures. The intersections of filaments form dark matter halos. Baryonic matter (or "gas", i.e., the visible matter described by the standard model of particles physics) accretes along the filaments into dark matter halos, which then cools, condenses, collapses and forms stars, making galaxies shine. It is also known that galaxies host supermassive black holes (SMBHs) within their centres, which also accrete gas and grow with time. The structure formation process is not a one-way road, however. Radiation from massive stars, supernova explosions, and accreting SMBHs deposit a large amount of energy and momentum into the surrounding gas. Collectively, these feedback processes drive large-scale galactic outflows, which brings mass, energy and heavy elements back into the cosmic web. In brief, galaxy formation and evolution are highly regulated by gas accretion from the intergalactic medium and energetic outflows powered by feedback processes. The existence of magnetic field and cosmic rays further complicates the picture by providing non-thermal supports and pressure gradients which facilitate large-scale outflows. The circumgalactic medium (CGM), i.e., gas directly surrounding galaxies, encodes precious information on gas flows in and out of galaxies. Thus, it is under intensive multi-wavelength observations recently with both absorption and emission techniques. Observations have revealed a highly complex, multiphase nature of the CGM that is dependent not only on feedback but also on small-scale instabilities and cooling processes. The vast dynamical scales involved in these processes make it highly challenging to simulate the galaxy-CGM ecosystem, and the large variety of the observational probes and the complexity of the signals make it difficult to interpret the data. In this project, we simulate the formation and evolution galaxies throughout cosmic history in advanced supercomputers, starting from the initial density perturbation imprinted at the time of Big Bang, until the present day. This "virtual Universe" provides us rich data on how galaxies co-evolve with their environment, the CGM. The simulations include state-of-the-art solvers or models for star formation, black hole formation and accretion, feedback, radiation transport and magnetic fields. We further construct complete pipelines to create synthetic observations of the CGM, including absorption features on the spectra of background quasars, and emissions from hydrogen atom and various metallic atoms, ions and molecules. These data are tested against observations at different wavelengths, for example from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope and the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT). They will also be used to predict observations of the future Atacama Large Aperture Submillimeter Telescope (AtLAST) and also from the recently launched James Webb Space Telescope (JWST). We found that the circumgalactic gas exhibits complex origins and structures, and is sensitively dependent on the mechanisms that drive galactic outflows.

The project has resulted in 20 peer-reviewed papers (19 published, 1 in press), and 3 articles currently in the reviewing process. The main results are: 1) State-of-the-art simulations of galaxy formation and isolated galaxies were performed, with various simulation codes and stellar feedback models. 2) We have made great advance in understanding the origins and evolution of the circumgalactic media (CGM) around galaxies. 3) Major code developments were accomplished, in particular a fast algorithm for radiative transfer for investigation of stellar radiation on the CGM, and a full MHD solver to simulate non-thermal pressure and galactic winds. 4) We have built complete analysis pipelines for producing mock observational hydrogen Lyman-alpha emissions together with self-consistent transport for ionizing radiation. 5) We further explored CGM emissions from metal and molecular lines, which greatly complement the knowledge we gained from Lyman-alpha emission lines. The project has entailed tight collaborations between the extragalactic group of the Institute of Theoretical Astrophysics, UiO and several leading international research groups on the CGM and galaxy formation. The simulation codes developed during this project will potentially greatly benefit the entire Gasoline/ChaNGa code collaboration, one of the major international communities for cosmological simulations. Several participants (including PhD students and postdocs) in the project are now involved in future collaborative projects from the USA, Canada, and Switzerland. Moreover, the experience and expertise on developing massively parallel simulations has lead ITA/UiO to be the Norwegian partner of an EuroHPC consortium, which is dedicated to improve astrophysics codes for next-generation exa-scale HPC systems. Last but not least, the simulation data products, analysis pipelines, and mock observational data are being used by observers for interpreting current data and predicting future observations. For example, the CGM line-emission mock data are used in the EU-funded AtLAST Design Study for planning the next-generation submillimeter telescope. These activities have increased the visibility of Norwegian research on extragalactic astrophysics and high-performance computing. For a public outreach, we plan to write an article on, UiO's research newsletter for science and technology, about galaxy formation and evolution, the supermassive black holes, and how high-performance computers and AI technique help us to simulate and understand such complicate systems. In addition, we will organise planetarium/activities for the "Ungforsk" conference in the coming years for students in 10th grade and VG1 to gain knowledge on modern research in extragalactic astrophysics. In connection with international space missions (e.g., the launch of the JWST and the EUCLID satellite), with these activities we hope to spark the interest of young students to pursue a career in science.

Understanding the formation and evolution of galaxies is a primary goal in modern cosmology, and studies of the ionisation, chemical, thermodynamic, and kinematic states of gaseous material directly surrounding the galaxies, the circumgalactic medium (CGM), hold clues to understanding the mass, metal and energy exchange between galaxies and thus the galaxy formation process itself. We propose a comprehensive study of the baryon cycles in and out of galaxies and the CGM using state-of-the -art cosmological galaxy formation simulations. The simulations will be performed using two leading hydrodynamic codes, Gasoline2 and Arepo, each with its own well-tested models for star formation, stellar feedback and AGN feedback. Such a variety of feedback models enable us to test how sensitively the CGM depend on different feedback processes. The simulation data will be post-processed to produce synthetic absorption spectra and Lya emission maps, which will then be compared extensively with existing observational data at all redshifts. We will study how these observed properties depend on galaxy mass, star formation history and structure, providing invaluable insight for interpreting upcoming observation data from next generation telescopes and satellites, such as Euclid and E-ELT. Once accomplished, this project will also be the first theoretical study to explore the connection between the Lya emitting gas and the Lya and metal absorbers.

Publications from Cristin

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Funding scheme:

ROMFORSK-Program for romforskning