2011/08/31 by Konstantinos Tassis, Nickolay Y. Gnedin, Andrey V. Kravtsov
Physics and Astronomy · #Astronomy and Astrophysical Research #Dwarf galaxy #Dwarf spheroidal galaxy #Electrical and Electromagnetic Research #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy formation and evolution #Metallicity #Population #Star formation #Stars #astro-ph.CO
paper · pdf · doi:10.1088/0004-637x/745/1/68
7 pages, 4 figures, accepted for publication in ApJ
arxiv created 2011/10/22 · openalex publication_date 2011/12/29 · arxiv updated 2015/05/29 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The close relation of star formation with molecular gas indicated by observations and assumed in recent models implies that the efficiency with which galaxies convert their gas into stars depends on gas metallicity. This is because abundance of molecular hydrogen is sensitive to abundance of dust, which catalyzes formation of H 2 and helps to shield it from dissociating radiation. In this study, we point out that in the absence of significant pre-enrichment by Population III stars forming out of zero metallicity gas, such H 2 -based star formation is expected to leave an imprint in the form of bi-modality in the metallicity distribution among dwarf galaxies and in the metallicity distribution of stars within individual galaxies. The bi-modality arises because when gas metallicity (and dust abundance) is low, formation of molecular gas is inefficient, the gas consumption timescale is long, and star formation and metal enrichment proceed slowly. When metallicity reaches a critical threshold value star formation and enrichment accelerate, which leads to rapid increase in both stellar mass and metallicity of galaxies. We demonstrate this process both using a simple analytical model and full cosmological simulations. In contrast, the observed metallicity distributions of dwarf galaxies or stars within them are not bi-modal. We argue that this discrepancy points to substantial early stochastic pre-enrichment by Population III stars to levels Z ∼ 10 −2 Z ☉ in dense, star-forming regions of early galaxies.