Letters of Intent received in 2017

LoI 2019-1988
Outside-in and Inside-out: The IGM around galaxies and quasars

Date: 17 June 2019 to 21 June 2019
Location: Abbazia di Spineto, Italy
Contact: Avery Meiksin (meiksin@staffmail.ed.ac.uk)
Coordinating division: Division J Galaxies and Cosmology
Co-Chairs of SOC: Avery Meiksin (University of Edinburgh)
Joseph Hennawi (UC Santa Barbara)
Valentina D'Odorico (INAF)
Jason X. Prochaska (Lick Obs/ UC Santa Cruz)
Co-Chairs of LOC: Avery Meiksin (University of Edinburgh)
Valentina D'Odorico (INAF)



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 ionization
b. Sources of helium ionization
c. The thermal history of the IGM
d. Spectral shape of the ionizing background and the nature of the sources

4. New IGM experiments with future facilities



The study of the Intergalactic Medium has expanded rapidly over the past several years. It has most recently been forging increasingly strong links with galaxy formation, the interstellar medium of galaxies and the reionization of the IGM. Major new facilities like DESI and JWST will soon come online and together with MUSE and KCWI will enable detailed probing of the IGM in both absorption and emission, especially of the gas in and around galaxies. Numerical simulations of the IGM and of galactic and AGN feedback on the IGM are reaching unprecedented levels of detail and accuracy. The timing of summer 2019 is just right for conveying first results from facilities that will have just come on line, and for discussing plans for new major facilities that will soon be delivered.

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 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 launch date for JWST is October 2018.

Recent IGM meetings have been held in Cambridge (2011), Edinburgh (2013), Heidelberg (2014), Berlin (2016), and a meeting on galaxies and the CGM in Durham (2017), each of which had 100-200 participants. The only previous IAU Symposium on the IGM was IAUS 217 "Recycling Intergalactic and Interstellar Matter" in 2004.

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.