Doctoral defence: Toni Tuominen “Missing baryons and the large-scale structure of the universe”

On 10 March at 13:00 Toni Tuominen will defend his doctoral thesis “Missing baryons and the large-scale structure of the universe” for obtaining the degree of Doctor of Philosophy (in Physics of Galaxies and Cosmology).

Supervisor:
Associate Professor Jukka Nevalainen, University of Tartu

Opponent:
Professor Emeritus Mauri Valtonen, University of Turku (Finland)

Summary
Currently, we have a good understanding of how much ordinary matter (i.e. baryons) there is in the Universe: ~5%. The rest are the mysterious dark matter and energy. However, in the nearby Universe, half of the baryons remain unobserved. This discrepancy between the expected and observed baryon fractions is known as the problem of the missing baryons.

Since the observational signal of the missing baryons falls below the sensitivity of our instruments, the problem is seemingly of an observational nature. Thus, we used the cosmological simulation EAGLE to gain theoretical understanding of the distribution and thermodynamic properties of the missing baryons. Earlier theorethical studies concluded that the missing baryons are in the hot intergalactic gas, residing within cosmic filaments. We continued upon this by applying algorithms, such as the Bisous method, to detect this filamentary network. We then characterised the hot intergalactic gas within the detected filaments. In addition, given that galaxies and the intergalactic gas co-exist in the same large-scale structures, we studied the distribution of the luminosities of simulated galaxies. This allowed us to select a sample of optimal filaments, containing the highest densities of missing baryons. In essence, the best regions to search for the yet unobserved ordinary matter is in the cores of filaments, located in regions with a high density of galaxy luminosity.

Finally, we studied the prospect of using highly ionised Oxygen to trace the missing baryons. Being observable in the X-ray range, OVII is a candidate to track the hot intergalactic gas. Unfortunately, based on our results on the EAGLE simulation, there is not enough OVII in filaments to trace the missing baryons. Nonetheless, the results presented in our work on the distribution of both the missing baryons and OVII within cosmic filaments will aid in planning future X-ray observations.

The defence will be held also in Zoom: https://ut-ee.zoom.us/j/99557567769?pwd=cy9wWUZjUWdpVXY4QjAvdzJxMGc0QT09. Meeting ID: 995 5756 7769, Passcode: 679441.