Letters of Intent received in 2018

LoI 2020-2024
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 -- how can local feedback processes provide constraints on feedback during 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, our understanding of magnetized halos and magnetized outflows has become enriched and
broadened. The 1990s version of the simple disk-halo concept of local stellar venting has now been superseded 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.
Please note that 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 20 to August 14, 2020.