Dr Yin-Zhe Ma from UKZN will present the NASSP Colloquium with a talk entitled, " Where are the baryons in the Universe?"

Previous studies of galaxy formation have shown that only 10 per cent of the cosmic baryons are in stars and galaxies, while 90 per cent of them are missing. Hydro-dynamical simulation shows that the missing baryons are in a state of diffuse plasma with temperature 10^5 to 10^7 Kevlin, which is hard to be directly observed by X-ray observations. In this talk, I will present three observational studies that coherently find significant evidences of the missing baryons. The first is the cross-correlation between the kinetic Sunyaev-Zeldovich maps from Planck with the linear reconstructed velocity field. We find significance (4.6 sigma) detection of the peculiar motion of gas on Mpc scales, for which we fit the baryon fraction. The second study is the cross-correlation between the thermal Sunyaev- Zeldovich effect with gravitational lensing map and fit the data with halo model. The third study is to stack the pairs of luminous red galaxies and subtract the halo contribution, which leads to the detection of gas within filaments. These studies show that the baryons are neither too hot nor too cold but are diffused till 5 virial radius of dark matter halos, which help us to understand the process of galaxy formation.

Dr Ma is a Senior Lecturer at University of KwaZulu-Natal, he obtained his PhD in Astronomy from University of Cambridge, and then spent 3 years at University of British Columbia (Canada) as a CITA national postdoc fellow, and another 1-year at Jodrell Bank Centre for Astrophysics at University of Manchester, UK.
His research is mainly on radio astronomy and cosmology. He also has strong interests in testing general relativity and extreme physics with various astronomical observations. He believes that the future multi-tracer observations (such as galaxy surveys, neutral hydrogen survey etc) can give us a clearer and correct understanding of the cosmic evolution.
He is currently a member of SKA (Square Kilometer Array) team, Planck satellite of European Space Agency, BINGO experiment (BAO as Integrated Neutral Gas Observation) and 6dFGS (six-degree-Field Galaxy Survey).