The Golden Mass of Galaxies and Black Holes

Prof. Avishai Dekel


This talk will address the preferred mass and time for galaxy formation, in dark-matter haloes similar to that of the Milky way but when the Universe was a few Gigayears old. It is proposed that this is due to the interplay between two mechanisms, first *supernova* feedback that removes gas from the galaxy, and second *hot gas* in the deep potential well of massive haloes that suppresses cold gas supply to the galaxy, the two being effective in galaxies of lower and higher masses respectively. Cosmological simulations reveal that the same mechanisms are responsible for a robust sequence of events were galaxies undergo a dramatic gaseous *compaction*, sometimes caused by mergers, into a compact star-forming “blue nugget”. This triggers inside-out *quenching* of star formation, which is maintained by a hot massive halo aided by black-hole feedback, leading to todays passive elliptical galaxies. The blue-nugget phase is responsible for drastic transitions in the main galaxy structural, kinematic and compositional properties. In particular, the growth of the *black hole* in the galaxy center, first suppressed by supernova feedback when below the critical mass, is boosted by the compaction event and keeps growing once the halo is massive enough to lock the supernova ejecta by its deep potential well and the hot halo. The compaction events also trigger the formation of extended rings in high-z massive galaxies. These events all occur near the same characteristic halo mass, giving rise to the highest efficiency of galaxy formation and black-hole growth at this magic mass and time.


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About the talk

The Golden Mass of Galaxies and Black Holes
Prof. Avishai Dekel
Hebrew University of Jerusalem
Thursday May 28, 2020 - 10:30 GMT+1  (Online)
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About the speaker

Avishai Dekel is a professor of physics at the Hebrew University of JerusalemIsrael, holding the Andre Aisenstadt Chair of Theoretical Physics. His primary research interests are in astrophysics and cosmologyDekel earned his Ph.D. from the Hebrew University in 1980, and was a research fellow at Caltech and assistant professor at Yale University before joining the faculty of the Hebrew University in 1986.

Dekel is known for his contributions to research in cosmology, especially the study of the formation of galaxies and large-scale structure in the Universe, which is dominated by dark energy and dark matter.  His expertise is dwarf galaxies and supernova feedback, large-scale cosmic flows and early estimates of fundamental cosmological parameters, the structure of dark-matter galactic halos, and the theory of galaxy formation.

His research focuses on galaxy formation in its most active phase at the early universe, using analytic models and computer simulations. He studies how continuous streams of cold gas and merging galaxies from the cosmic web lead to star-forming disks and drive violent gravitational disk instability, and how this instability leads to the formation of compact spheroidal galactic components with central massive black holes.