Science Questions

Q1: Quenching and the cessation of star-formation

• Is quenching a good word to describe the end of star-formation activity in galaxies?
• Is the apparent sSFR dichotomy real, and is it a fair statement that galaxies are either star-forming or quenched?
• Is quenching a one-way process or do quenched galaxies ever return to the Main Sequence?
• How many quenching pathways are there - one, two, many?
• What are the timescale(s) for quenching?
• Is quenching due to starvation or gas expulsion?
• Do galaxies stay quenched because of internal or external factors?

Q2: The Role of Gas

• Is star-formation in disks regulated by inflow, or by outflow, or by atomic-molecular conversion?
• On what scales is "stellar feedback" relevant?
• Does star formation differ at low and high redshift?
• Do the accretion and ISM properties vary with space and time?

Q3: Quenching and morphology/structure

• Is there a disk-spheroid structural dichotomy in most galaxies?
• Can disks be transformed into spheroids except through major mergers?
• Is the stellar mass growth produced in major mergers important?
• Do bars and spiral structure play an important role in galaxy evolution?
• What are the timescales for morphological/structural changes?
• How closely are star-formation activity and morphology/structure correlated?
• How does structure/morphology change when galaxies cease forming stars, and is this just superficial (in light) or profound (involving mass redistribution)?
• Does the structure, e.g. surface density, physically drive the quenching process(es)?
• Is the link between structure/morphology and sSFR cause or effect and how is this linked to size evolution?

Q4: The role of environment

• Does the wider environment on halo and above-halo scales drive the evolution of a galaxy in terms of star-formation rates and/or the morphology/structure of a galaxy?
• Does the halo drive the quenching of galaxies, and if so, how?
• Is the quenching of satellites due to the same effects as the quenching of centrals, or are there additional satellite-specific (or central-specific) processes that are playing a significant role?
• Is the morphology density relation important, or just a reflection of other effects?
• What is the significance of conformity and does conformity exist on super-halo scales?
• What are the timescales for environmental influences?

Q5: The role of black holes

• How tight are the different scaling relations between galaxy properties and black hole mass?
• Do these scaling relations evolve, and what does this tell us?
• How tight is the claimed co-evolution of black holes and galaxies, and what are the implications for the evolution of the scaling relations?
• Do black holes play a significant role in regulating their own growth, in regulating the level of continuing star-formation in their hosts, and/or in quenching their hosts through either local or halo-wide processes?

Q6: The cosmological setting

• Are galaxies ultimately simple manifestations of cosmic structure formation or are they complex organisms influenced but not controlled by the larger Universe around them?
• What physics sets the limit in growth of stellar mass of galaxies, and why do galaxies quench just as they reach high efficiencies in baryonic conversion into stars?