Framing the Big Picture of Galaxy Star Formation Quenching with JWST & Euclid


30 September - 4 October 2024


Most star-forming galaxies grow in mass along the so-called star formation (SF) main sequence (Brinchmann et al. 2004; Noeske et al. 2007, Elbaz et al. 2007) where their star formation rate (SFR) is proportional to their stellar mass (M). Some galaxies deviate from the SF main sequence, e.g. during a starburst episode (when the SFR can increase by several orders of magnitude) or, on the contrary, when the star formation slows down or stops, temporarily or permanently. Well documented over more than 12 billion years, the continuous increase of the fraction of quiescent galaxies (where star formation has stopped) is the statistical expression of the so-called quenching, i.e. the lasting —if not permanent— shutdown of galaxy star formation. Such quenching of the star formation requires, however, mechanisms able to suppress and prevent cold-gas infall, which we may expect to vary depending on galaxies life experience. The diversity of quiescent galaxies that is observed since cosmic noon (e.g. in terms of stellar mass and morphology) argues indeed for the coexistence of different quenching channels (Faber et al. 2007, Peng et al. 2010, Schawinski et al. 2014, Moutard et al. 2016b).

To trace those different quenching channels and track associated physical processes since cosmic dawn, one needs to probe all kinds of galaxies (in terms of star formation rate, stellar mass, morphology, environments, AGN activity, etc.) back to the time when the first galaxies formed. From an observational point of view, the solution consists in combining surveys of decreasing area and increasing depth, following a wedding-cake approach. While the Euclid Deep Fields and Calibration Fields are ideally designed to probe galaxy evolution from cosmic noon, large JWST surveys like COSMOS-Web, PRIMER, JADES, or MIDIS are ideal to probe galaxies in the deep Universe, from cosmic dawn. In that respect, recent debate about the nature of JADES-GS-z7-01-QU —a z ~ 7 Lyman-break galaxy with apparent lack of emission lines (Looser et al. 2023, Faisst et al. 2024)— has stressed the need to properly (re)define what a quiescent galaxy is and what we do mean by quenching.

In this light, the present workshop is dedicated to framing the big picture of galaxy star formation quenching, by assembling both renowned and emerging experts whose record demonstrates an original approach and/or a long-lasting effort to tackle the question, from various perspectives: quiescent/green-valley galaxy identification, galaxy star formation histories, galaxy morphological evolution, galaxy-LSS interactions and galaxy-SMBH co-evolution, from either an observational or a theoretical point of view. The workshop is not specifically meant to showcase new results but rather to foster discussions aiming in particular at 1. proposing unambiguous definitions of the terms quiescent and quenching, 2. reviewing the different quenching channels and their mechanisms and 3. determining the best strategy to leverage the combination of JWST and Euclid surveys.