Letters of Intent for 2015

LoI 2015-194
Focus Meeting: Stellar structure, gas dynamics and star formation in galaxies

Date: 10 August 2015 to 11 August 2015
Location: Honolulu, United States
Contact: Sharon Meidt (meidt@mpia.de)
Coordinating division: Division H Interstellar Matter and Local Universe
Co-Chairs of SOC: Eva Schinnerer (MPIA)
Tony Wong (University of Illinois)
David Meier (New Mexico Tech)
Richard Rand (University of New Mexico)
Co-Chairs of LOC: Juan Carlos Munoz (ESO)
Sharon Meidt (MPIA)
Annie Hughes (MPIA)



1. Molecular gas in a galactic potentials: environmental variations in galactic structure and gas stability; response of gas to bars, bulges and spiral arms; variations in dense gas fractions, chemistry, CO-dark gas and molecular/atomic ISM phase balance with galactic environment; the impact of the galactic potential on molecular cloud evolution/environmental variations in GMC properties; GMC formation/destruction mechanisms in different galactic environments; truncations in CO/stellar disks - a physical connection?

2. Global patterns of star formation in galaxies: cluster properties, cluster formation, star formation efficiencies and modes of star formation in different galactic environments. Link between galactic structure and regions where SF is especially efficient/inefficient.

3. Molecular gas and star formation in special locations: distribution and properties of molecular gas and star formation in early-type and dwarf galaxies, the outer disks of galaxies, galaxy centers; extraplanar molecular gas. How much? How common? What are the best observational tracers?

4. Molecular gas and star formation across the Hubble Sequence: do galactic structure, stellar mass affect empirical correlations between SF and molecular gas? what drives the scatter in the KS relation within and among galaxies? the importance of stellar feedback vs. global galaxy structure on cloud stability: is there a stellar mass/gas fraction where one dominates the other?

5. Molecular gas and star formation through cosmic time: evolution in the structure of galactic potentials, SFRs and molecular gas fractions; exploring the impact of gas torquing on the starburst-interaction/merger connection

6. Astrochemistry in external galaxies: progress and possibilities: Molecular line emission and chemistry as a diagnostic tool for physical conditions in molecular gas, cloud evolution, feedback mechanisms and galaxy evolution; tracing molecular mass in different regimes and at different redshifts.



The galactic potential dictates where stars form by channeling gas via non-axisymmetric (bar and spiral) structures and by governing the radial distribution of ISM phases. Recent evidence from Galactic and extragalactic surveys suggests that the `how' of star formation may be just as intimately related to the galactic potential: the seeds of star formation, molecular clouds, are not universal as once thought, but depend on the galactic environment in which they reside. How
do clouds inherit their properties from their surroundings? What role do spiral arms play in cloud evolution through agglomeration/collisions and tidal torques? What are the (external) forces that act on clouds and how do they compare with those acting on small scales (turbulence, magnetic fields, star formation feedback)? Under which conditions do clouds form stars? We aim to bring two communities together to answer these questions, putting the dynamics and structure of disk galaxies into dialogue with conditions in the ISM and star formation.

By 2015, ALMA will have mapped the dense gas distribution at cloud-scale resolution in multiple nearby spiral galaxies, building on campaigns begun by CANON and PAWS. Together with large infrared surveys (such as Spitzer/S4G and WISE/WERGA) that have recently revealed the backbone of the stellar potential, this will complete the inventory of baryons in the disks of these systems. For the first time it will be possible to bridge the large and small scales of star formation across a diversity of galaxy types: we can view the (morphological and kinematic) context of the star-forming gas at the same time as study cloud-scale phenomena at the heart of star formation. This synergy makes the IAU General Assembly in Honolulu the optimal time for such a discussion.

The two communities we aim to engage have so far had little interaction with each other: gas is thought to play a negligible dynamical role in a galaxy given its minor contribution to the total mass, while local processes are thought to
dominate the organization of molecular gas into its star forming entities. But gas clearly impacts the way galaxies build in mass in their outskirts, how bulges grow over time, and how we dissect the vertical structure of disk
galaxies. How gas forms stars is furthermore potentially key to unravelling the nature of the structural change from disk-dominated to elliptical galaxy that accompanies quenching. Meanwhile, galaxy structure is a crucial ingredient for star formation: we need a complete census of the physical processes (large-/small-scale, internal/external) acting on clouds in order to understand the conditions under which star formation can proceed.