Letters of Intent received in 2017

LoI 2019-2013
Magnetized Galactic Halos and Feedback

Topics

1. Local environments of galaxies
2. The disk-halo connection -- new observations and theory
3. Halo Kinematics and lagging halos (e.g. HALOGAS, IMAGINE, MaNGA)
4. Magnetized halos -- importance of magnetic fields (e.g. CHANG-ES)
5. Inflow versus Outflow -- observational & theoretical arguments
6. Feedback -- AGNs versus starbursts
7. The connection between local galaxies and distant universe -- what can local feedback tell us about galaxy formation?

Rationale

It has been several decades since there has been an IAU Symposium related to the disk-halo connection in galaxies (IAU Symp. 144, Leiden, the Netherlands, 1990). Over those years, an abundance of information, both observational and theoretical, has been brought to bear on the problem of disk-halo dynamics and the time is ripe for a new look at this important aspect of galaxy structure and evolution.

We now see that the `disk-halo connection' should not be seen in isolation, but rather as a key element of galaxy formation and evolution. The magnetic field, for example, can no longer be seen as a small perturbation on halo dynamics. New observational and theoretical evidence are not only revealing magnetic fields in galaxy halos, but linking these fields to galactic dynamos. For example, the CHANG-ES (Continuum Halos in Nearby Galaxies -- an EVLA Survey, Irwin et al. 2012, AJ, 144, 43 and subsequent papers) survey is revealing never-before-seen magnetic structures in galaxy halos that beg further active and informed discussion. Such discussion is not restricted only to edge-on galaxies but is more widely applicable to systems with other orientations.

At the same time, halo lags have also become accessible observationally and appear to be present in many spiral galaxies, as revealed by surveys such as HALOGAS and IMAGINE for HI as well as the MaNGA survey for ionized gas (e.g. Bizyaev et al. 2017, ApJ, 839, 87). Still a young science due to observational challenges, the study of halo kinematics is now maturing with many new and surprising results. Original explanations via gaseous fountains were unable to adequately explain the observed kinematics; galaxy dynamos (Henriksen & Irwin, 2016, MNRAS, 458, 4210) and possibly infalling gas (above Bizyaev reference) both of which are related to nearby environments, have now been proposed.

The issue of `feedback' from galaxies is an outstanding and necessary step in galaxy formation scenarios. Yet, local galaxies show feedback at spectacular resolution in comparison to distant galaxies. Such feedback is related to active galactic nuclei (AGNs) and/or starbursts and/or disk-halo outflows. If we understand the processes that we see in nearby galaxies, the important link to distant forming galaxies can be strengthened. Some of the most dramatic examples of feedback are clearly seen in nearby systems. By the time of the proposed meeting, there should also be significant HST spectroscopic observations of quasar absorption lines which will provide a crucial link between local and distant systems.

The timing is right for such an IAU Symposium. Aside from the fact that many years have passed since a related IAU symposium, the emergence of our understanding of magnetized halos and magnetized outflows has become enriched and broadened. The 1990s verison of simple disk-halo concept of local stellar venting has now been superceded by global and fundamental approaches. In this pre-SKA era, it is time for a focused effort which will bring together experts in fields of related interest. More than local stellar venting is at stake.

Please note that the venue and exact dates have yet to be determined. However, given restrictions on the scientists who should be at the meeting, our window is between approximately July 22 to August 16, 2019.