Description:

"Stellar-feedback regulated black hole growth: confinement by gravity and circumgalactic gas"

Lindsey Byrne, PhD Student, Northwestern University

Recent simulations of galaxy evolution suggest that supermassive black holes grow in two phases: inefficiently and intermittently at early times, and more rapidly later on. In this talk, I will discuss physical factors that may drive the transition between black hole accretion phases in the context of the FIRE simulations. I select a set of high-resolution hydrodynamical cosmological zoom-in simulations ranging from dwarf galaxies to galaxies sufficiently massive to host luminous quasars. I find that several properties of the galaxy across a range of scales, including halo mass, galaxy stellar mass, and stellar surface density in the central 1 kpc, correlate with rapid black hole growth: simple, constant thresholds in these properties are crossed around the time of the transition from suppressed to accelerated growth. I will discuss how the confinement of stellar feedback may explain the phases of black hole accretion and propose two mechanisms by which this could occur: gravitational confinement from high stellar surface densities in the nucleus, and pressure confinement from a virialized CGM.

"Signatures of criticality in the physical structure of the brain"

Helen Ansell, Postdoctoral Scholar, Northwestern University

The highly complex structure of the human brain contains billions of intricately branched neurons that are interconnected via trillions of synapses. Many aspects of the physical structure of brain tissue and its relation to brain function remain poorly understood. In this talk, I will discuss our ongoing investigation into physical properties of the cellular structure of the brain, enabled by newly-released millimeter-scale brain volume reconstructions. Using techniques from statistical physics, we show that the complex physical structure of the brain displays signatures of structural criticality, including fractality and long-range correlations. Moreover, we find that the resulting scaling exponents are consistent across multiple organisms, indicating universality. Our results suggest that a few key parameters control the large-scale physical properties of the brain, thereby paving the way towards creating generative models that mirror the physical properties of brain structure. 

Speakers:

Lindsey Byrne, Graduate Student, Northwestern University

Helen Ansell, Postdoctoral Scholar, Northwestern University