Letters of Intent received in 2016

LoI 2018-1885
The Intergalactic Medium: Outside-In and Inside-Out

Topics

1. Tests of cosmological models
a. Results from DESI
b. Modelling
2. The galaxy-IGM connection
a. The CGM in absorption
b. CGM and cosmic web imaging in emission
3. Reionization and the ionizing background
a. Sources of hydrogen and helium ionization
b. The thermal history of the IGM
c. Spectral shape of the ionizing background
4. New IGM experiments with future facilities

Rationale

The past twenty years has witnessed a revolution in our understanding of the physical origin and nature of the IGM. Numerical simulations have shown that its structures are a natural part of cosmological structure formation in a Cold Dark Matter dominated universe with a cosmological constant (LCDM). Advances in IGM observations have allowed the various contributions to the UV metagalactic ionization background to be quantified over a broad range of redshifts, informed our understanding of the process of hydrogen and helium reionization and have become an essential tool for interpreting measurements of the gaseous environment of galaxies, the Circumgalactic Medium (CGM), and its role as both reservoir and arena of galaxy formation and feedback.

Observational studies of the IGM continue to thrive, with sample sizes now pushing the limits of Big Data. The Dark Energy Spectroscopic experiment, DESI, designed to measure the dark energy equation of state by tracking the evolution of the Baryonic Acoustic Oscillation signal, is expected to boost the number of QSOs for studying the statistics of IGM density fluctuations by a factor of ten, to a million. First light for DESI is January 2018, so that the meeting is especially timely for this major experiment. High accuracy spectrographic observations continue to probe the structure of the CGM with increasing precision. Very recently developed 3d integral field spectrographs which aim to detect emission from the IGM, MUSE and CWI, are now delivering the first images of the interface between the cosmic web and galaxies. The next-generation KCWI is scheduled to begin observations in 2017.

Recent IGM meetings have been held in Cambridge (2011), Edinburgh (2013), Heidelberg (2014) and Berlin (2016), which had
100-200 participants. The only previous IAU Symposium on the IGM was IAUS 217 "Recycling Intergalactic and Interstellar
Matter" in 2004. As a newly established Commission (J2), we request the 2018 IAU AGM to host the Commission's first.

While the focus is on the IGM and CGM, there is a natural cross-over with interstellar medium studies in the area of star-formation feedback, especially the driving of metal-enriched winds, and its impact on the CGM/ IGM. Commission J2 is cross-listed with Division H: Interstellar Matter and Local Universe for this reason. We will plan also to feature contributions from members of the ISM community with overlapping interests. The Commission is similarly cross-listed with Division B: Facilities, Technologies and Data Science. We will include not only members of DESI, but invite contributions about facilities that will impact IGM studies in the future, such as JWST, GMT, TMT, E-ELT and LSST, to devote some time for discussion of science goals using these instruments.

We will plan a programme to develop major advances in observations and theory and discuss plans for new programmes to address the key questions in IGM science.

We have made an effort to achieve a balanced composition of the SOC in terms of gender and geographic diversity. We will
seek to do the same in developing the programme and also to include IGM and IGM-related topics of a wide interest well
suited to the environment of an IAU AGM.

SOC Members: Along with SOC chairs, the following individual have agreed to be members of the SOC:

Hsiao-Wen Chen - University of Chicago - USA
Sebastian Lopez - University of Chile - Chile
J. Xavier Prochaska - Lick Observatory - USA
Emma Ryan-Weber - Swinburne University of Technology - Australia
Joop Schaye - Leiden Observatory - The Netherlands
Raghunathan Srianand - IUCAA - India