Letters of Intent received in 2017

LoI 2019-1998
Galaxy Assembly: The Emergence of Bars and Bulges

Date: 11 November 2019 to 15 November 2019
Category: Non-GA Symposium
Location: IUCAA, Pune, India, India
Contact: Kanak Saha (kanak@iucaa.in)
Coordinating division: Division J Galaxies and Cosmology
Other divisions: Division H Interstellar Matter and Local Universe
Co-Chairs of SOC: Saha Kanak (IUCAA, Pune)
Combes Francoise (Obs Paris)
Chair of LOC: Saha Kanak (IUCAA, Pune)



This Symposium will bring together people who attack the core problem of
bar/bulge formation and evolution from these different directions.
Major issue to address include:

1. Empirical confirmation of the dynamical predictions that bulges form well after bars and embedded in the long planar bars.
2. The relation of thick discs to thin discs and bar/bulges.
3. The distribution in radius, angular momentum and time of inflalling gas that drives disc and bulge growth.
4. Temporal variation in thickness of star-forming disc.
5. Star formation history and stellar populations in the bar/bulges.
6. Contribution of the bar/bulge to heating and mixing chemically the stellar discs.
7. The role of resonant excitation in structuring disc.

8. Impact of environment, through gas accretion and tidal interaction on the bar/bulge formation.
9. Influence of the dark halo on the bar/bulge growth.
10. The extent to which bar/bulges host “classical” spheroids formed in major mergers.



Scientific Rationale

At least 60% of the disc galaxies that now dominate the cosmic star formation rate are barred. Within the widely accepted LCDM theory, it is now clear that powerful feedback from star formation separated many baryons from their host halo early on. These baryons have since drizzled in to form galaxies like ours by sustaining over many billion years star formation within a centrifugally supported disc. As the disc's contribution to the galaxy’s gravitational field grew, spiral structure strengthened and developed into a bar. By loss of angular momentum, the bar strengthened and in many cases buckled, to form a bar/bulge.

We can now probe this sequence of events by several channels: through near-IR observations of galaxies at z~2, the peak of the cosmic star-formation rate; through detailed three-dimensional observations with integral field units (IFUs) at 0<z<0.5; and through meticulous examination, star by star, of our own prototypical SBc galaxy using astrometry and photometry from Gaia (DR2 April 2018) and a large number of spectroscopic surveys. These surveys together with the astro-seismology from Kepler are enabling the major breakthrough of determining quite precise ages for millions of stars. On the theoretical side, the problem can be attacked with ab-initio zoom-in simulations of structure formation, which are beginning to be able to resolve thin discs and employ sophisticated feedback prescriptions. Good insights have also been gained from suites of carefully controlled N-body experiments. Finally, models of specific bar/bulges have been constructed by the Made to Measure technique. There is a very good timing to hold such a symposium in the GAIA era, while many spectroscopic surveys are becoming available, and to prepare for JWST and LSST.