The cluster vs. field stellar mass-size relation at z ~ 1: implications for galaxy size growth with decreasing redshift  

Jasleen Matharu
University of Cambridge
 

Abstract:
The cluster environment is known to be capable of altering the evolutionary paths of galaxies through a variety of mechanisms. High velocity dispersions are likely to suppress minor mergers between satellite galaxies. Galaxy clusters are therefore excellent laboratories for testing whether or not minor mergers drive the size growth of galaxies. By comparing the stellar mass-size relation of galaxies in both the field and cluster environments, it is possible to expose the dominant physical mechanisms driving galaxy growth in different environments. I will present results on the cluster mass-size relation from HST WFC3 and grism follow up to GCLASS – the largest spectroscopic survey conducted on 10 clusters at z~1. Using this large sample of cluster galaxies with reliable size measurements – and a field sample from the 3D-HST survey – I will demonstrate how minor merger suppression, BCG growth, ICL growth and the production of recently quenched galaxies can work simultaneously to maintain a stellar mass-size relation that is independent of environment at low redshifts.

Host: Allison Noble

How do supermassive black holes form in the early universe?  

Christina Eilers 
MPIA/University of California, Santa Barbara

Abstract:
Quasars are the most luminous non-transient objects in the universe and can be observed at the earliest cosmic epochs, providing unique insights into the early phases of black hole, structure, and galaxy formation. Observations of these quasars demonstrate that they host supermassive black holes (SMBHs) at their center, already less than ~1 Gyr after the Big Bang at z~6. The formation and growth of these SMBHs in such short amounts of cosmic time is a crucial yet unanswered question in studies of quasar and galaxy evolution. An important piece of the puzzle is the lifetime of quasars — the integrated time that galaxies shine as active quasars — but yet it remains uncertain by several orders of magnitude. I will present a new method to obtain independent constraints on the lifetime of high redshift quasars by measuring the sizes of their proximity zones, which is the region of enhanced transmitted flux around the quasars due to their own ionizing radiation. Using this method and comparing our measurements to radiative transfer simulations, we recently identified a population of quasars with very small proximity zones, indicating quasar lifetimes of only ~10,000 years. I will discuss the consequences of such short lifetimes on the quasars’ ionizing power, their black hole accretion rates, and highlight tensions with current theoretical models for black hole formation.

Host: Rob Simcoe