2024/04/10 by James Trussler, Christopher J. Conselice, Trussler, James +18 · 5 citations
Social Sciences · #Astrophysics of Galaxies (astro-ph.GA) #Education, Sociology, Communication Studies #FOS: Physical sciences
paper · pdf · doi:10.48550/arxiv.2404.07163
openalex publication_date 2024/04/10 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We develop a photometric search method for identifying smouldering galaxies at 5< z < 8, which are defined to have weak emission lines and thus generally have low specific star formation rates and may even be in a state of (temporary) quiescence. The deep NIRCam imaging (∼29.5 AB mag, 5σ) from the JADES second data release is essential for finding these systems, as they are faint, relatively quiescent dwarf galaxies (M_* ∼ 108-109 M_\odot) in the Epoch of Reionisation (EoR). Moreover, medium-band imaging is key, enabling a clear identification of the lack of emission lines in these galaxies, thus betraying their dormant flame. Owing to the young age of the Universe, combined with the likely bursty star formation in these first dwarf galaxies, conventional colour-selection methods like the UVJ diagram likely miss a large fraction of the quiescent population in the EoR. Indeed, we find that smouldering galaxies constitute a considerable fraction (0.05-0.35) of the EoR dwarf galaxy population (M_* ∼ 108-109 M_\odot). As predicted by simulations, these first dwarf galaxies are fragile, the star formation in their shallow potential wells easily snuffed out by feedback-driven winds triggered by secular or merger-driven starbursts, with the smouldering fraction increasing with decreasing stellar mass. Finally, we provide observational constraints on the smouldering galaxy comoving number density (∼10-4-10-5 dex-1 Mpc-3), which, although hampered by incompleteness, should aid in our understanding of the primordial baryon cycle, as current simulations greatly disagree on whether these systems are rare (∼1%) or common (∼50%) in the EoR.