Letters of Intent received in 2017

LoI 2019-1986
Connecting galaxy scaling relations

Date: 24 June 2019 to 28 June 2019
Location: Copenhagen, Denmark
Contact: Palle Moller (pmoller@eso.org)
Coordinating division: Division J Galaxies and Cosmology
Chair of SOC: Palle Moller (ESO, Garching)
Chair of LOC: Lise Christensen (Dark Cosmology Center)



The topics are effectively all galaxy scaling relations, but notably seen from the angle of "connecting relations observed via very different techniques" as described in the rationale below. In the rationale we also list the relevant groupings of those relations into our proposed "sessions", repeated here:
1) Relations involving metallicity, M*, gas kinematics, metallicity gradients
2) Relations involving molecular gas, SFR, M*
3) A_V, metallicity/dust, molecular gas
4) Kennicutt–Schmidt law, HI column density, SFR



Within the past decade galaxy scaling relations have evolved
from being mostly descriptive to become important tools in our
understanding of galaxy formation and evolution. All galaxies across the universe, and throughout its entire evolution, occupy only a tiny fraction of the full parameter space available, leading us to search for the underlying rules of physics which cause precisely this part of parameter space to be allowed. Classically those scaling relations have only been found and considered for emission selected (i.e. flux limited) galaxy samples, with the inherent limits on the tested parameter space. The flux limit effectively translates into a stellar mass lower limit which becomes increasingly severe at higher redshifts.

Within recent years similar, and apparently related, scaling elations have also been observed in absorption selected galaxy samples. Due to the selection via absorption those samples are not restricted to high galaxy masses, luminous galaxies or low redshifts. Absorption selected samples cover all galaxy masses at all redshifts. Being able to combine emission selected and absorption selected samples therefore holds a great discovery potential, allowing us to trace the evolution of scaling relations over many orders of magnitude in stellar mass, luminosity, star formation rates and metallicity, and throughout effectively the entire history of the universe back to at least a redshift of 6.

The task to connect those samples is not a simple one though. The
observable parameters in emission and absorption are not identical
and it is far from self evident how one may combine them. One clue
comes from the host galaxies of Gamma Ray Bursts (GRBs). Those
galaxies are often seen in both emission and absorption, and GRB
host samples may therefore provide important information on how
one may combine those samples. Detailed numerical simulations
tracing star formation, metal production, galaxy mass growth and
dynamical state of the gas, are also important keys to the process
of correctly connecting the scaling relations from the two vastly
different observational regimes. Conversely the combined scaling
relations will set boundaries which will help improve future

A first few attempts have been made to connect the stellar mass
metallicity (MZ) relation of absorption selected galaxies to
emission selected samples providing a relation covering some
5 orders of magnitude in stellar mass, and in the redshift range
from z = 5 to the present. The goal of this symposium is to
facilitate further connections. We aim to provide an environment
of interaction where observers of emission selected samples,
absorption selected samples, and GRB selected samples can
present their results, and discuss how those samples may best
be compared to, and connected with, each other. Further, in the
same sessions theoretical work and simulations will be presented
which will describe the relations from a modeling standpoint.

The main focus from the organizing team will be to foster and
encourage discussion and collaboration across some long standing barriers. This will be done by defining sessions by "type of relations" and then interleave emission, absorption and theory
presentations. We have formed a "core team" of experts of the
four individual themes:

Roberto Maiolino, Cambridge - emission selected studies
Joop, Schaye, Leiden - theory, simulations
Lise Christensen, Dark Cosmology Centre, Copenhagen - GRB hosts
Palle Møller, ESO Garching - DLA galaxies

We will expand this team, keeping in mind the rules and
recommendations of the IAU, as the preparations of the meeting
move forward.

The exact coverage of individual sessions will be defined when we
have the final team assembled, but our current draft contains four

1) Relations involving metallicity, M*, gas kinematics, metallicity gradients
2) Relations involving molecular gas, SFR, M*
3) A_V, metallicity/dust, molecular gas
4) Kennicutt–Schmidt law, HI column density, SFR

Ample time will be set aside for discussions in each session.