Discovery of a quiescent galaxy at z=7.3

Abstract

Local galaxies are known to broadly follow a bimodal distribution: actively star forming and quiescent systems (i.e. galaxies with no or negligible star formation activity at the epoch of observation). Why, when and how such bimodality was established, and whether it has been associated with different processes at different cosmic epochs, is still a key open question in extragalactic astrophysics. Directly observing early quiescent galaxies in the primordial Universe is therefore of utmost importance to constraining models of galaxy formation and transformation [1,2]. Early quiescent galaxies have been identified out to redshift z < 5 [3-9], and these are all found to be massive (M > 10 10 M ). Here we report the discovery of a quiescent galaxy at z=7.3, when the Universe was only 700 Myr old -about 5% of its current age. The JWST /NIRSpec spectrum of this galaxy from our JADES programme exhibits a complete absence of nebular emission lines, while the Balmer break and Lyα drop are unambiguously detected. We infer that this galaxy experienced a short and intense burst of star formation followed by rapid quenching, about 10-20 Myr before the epoch of observation. Particularly interesting is that the mass of this quiescent galaxy is only ∼4-6×10 8 M . This mass range is sensitive to various feedback mechanisms that can result in temporary or permanent quiescence. Therefore this galaxy represents a unique opportunity to learn more about galaxy formation and transformation in the early Universe [2,10].

Quiescent Low-mass Galaxies Observed by JWST in the Epoch of Reionization

“…The average duty cycle of quiescent and active galaxies clearly reflects these trends with stellar mass, slowly increasing from f duty ≈ 0.6 for M å ≈ 10 7.5 M e to ≈0.99 for M å 10 9 M e . Noticeably, the quiescent galaxy Lilium ( M M log 8.7  =  ) has a duty cycle f duty ≈ 0.84, which is consistent with the values obtained for JADES-GS-z7-01-QU using different stellar population synthesis tools by Looser et al (2023). For instance, when considering the values derived with BAGPIPES in Table 1 therein, 7 the time from the first star formation event is t obs − t form ≈ 40 Myr, and the time of active star formation is Δt on ≈ 30 Myr.…”

“…Lilium was selected among SERRA quiescent galaxies due to its similarity with JADES-GS-z7-01-QU in terms of stellar mass, duty cycle (Figure 3), and the time elapsed between SF quenching and observation redshift (Δt quench ∼ 15 Myr for Lilium versus Δt quench ∼ 10-40 Myr for JADES-GS-z7-01-QU). However, the stellar populations of Lilium are more metal-rich (Z å ≈ Z e ) than deduced by Looser et al (2023) for JADES-GS-z7-01-QU, Z å ≈ 0.01 Z e . In spite of these similarities, the SED we predict for Lilium (Figure 4, left panel) is too faint to match the one observed in JADES-GS-z7-01-QU.…”

“…Following this work, we define as quiescent those galaxies with no (or negligible) star formation activity at the epoch of observation. 4 According to Looser et al (2023), the spectral energy distribution (SED) of JADES-GS-z7-01-QU is consistent with a metal-poor M å ≈ 5 × 10 8 M e stellar population formed in a short and intense burst of star formation followed by rapid quenching (star formation rate (SFR) < 10 −2.5 M e yr −1 ), about 10-20 Myr before the epoch of observation. Given the rapidity of the transition from a starforming to a quiescent state for JADES-GS-z7-01-QU, its quenching is expected to have been driven by a fast process.…”

“…Thanks to JWST we can now study them and investigate the role of the various feedback processes in their evolution. Looser et al (2023) recently reported the discovery of a quiescent low-mass galaxy at redshift z = 7.3 (see also Strait et al 2023 for another very low-mass quiescent system at z = 5.2) from the JADES program, JADES-GS-z7-01-QU. Following this work, we define as quiescent those galaxies with no (or negligible) star formation activity at the epoch of observation.…”

An Extremely Compact, Low-mass Galaxy on its Way to Quiescence at z = 5.2

“…These debates have led to great interest in observations of quiescent galaxies increasingly early in the universe. However, possibly due to observational constraints, the majority of the literature about quiescent galaxies has focused on low-redshift, high-mass sources (with some exceptions, e.g., Santini et al 2022;Weaver et al 2022;Looser et al 2023). The highestredshift quiescent/post-starburst galaxies to date are at z = 7. followed then by several quiescent galaxies at z ∼ 2-4 (Glazebrook et al 2017;Schreiber et al 2018;Forrest et al 2020;Valentino et al 2020;Nanayakkara et al 2022;Marchesini et al 2023), most with stellar masses 10 10 M e .…”