After the big bang, nucleosynthesis started in the first stellar population formed in the Universe: population III stars (pop. III), and shortly after pop. II stars. When these pop. III stars became supernovae, they expelled metals (elements heavier than Helium) into the interstellar medium of the early Universe. The metals then formed the first dust grains by coalescence of the metals
Dust is a minor component in the Universe. However, it plays a major role: it affects ultraviolet (UV) through dust attenuation and reddening. Morecer, dust IR emission is a major cooling agent. This energy warms dust and is re-emitted at infrared (IR) and sub-millimeter (sub-mm) wavelengths.
Dust also plays a critical role in the formation of low-mass stars by facilitating several key processes in the interstellar medium (ISM). H2 formation is catalyzed on the surfaces of dust grains, making dust indispensable to initiating star formation even at warm temperatures. Furthermore, collisions between gas and dust grains enable efficient gas cooling, particularly at high densities, which promotes fragmentation of the cloud and the formation of low-mass stars. These low-mass stars may represent a transition population between Population III and Population II stars.
D. Burgarella and collaborators are publishing a paper investigating the coevolution of metals and dust for 173 galaxies at 4.0<z<11.4 spectroscopically observed by CEERS with NIRSpec. More specifically, the team have studied and analyzed the properties of a sample of galaxies that show an extremely low dust attenuation and try to understand the possible physical processes at play in these galaxies.
The analysis reveals a population of 49 extremely low dust attenuation galaxies (GELDAs) consistent with low stellar mass and no attenuation. The stacked spectrum of the GELDAs, confirms our finding that they suffer no dust attenuation.
Moreover, the proportion of GELDA is much higher at z ≳ 9 (83 % of the total sample) than at z ≲ 9 (26 % of the total sample). GELDAs become dominant in the early Universe.
The trends observed in the M_dust vs. M_star diagram feature an upper and a lower sequence linked by objects that can be transitional. A comparison with models suggests that we observe a critical transition at M_star ≈ 10^8.5 M_Sun, where we see galaxies dominated by stellar dust production, while other should have a contribution from grain growth through gas–dust accretion in the ISM.
All of our galaxies, including GELDAs at all redshifts, contain a large amount of gas that was not expelled from the galaxies, and a relatively normal star formation efficiency.
The population of high-redshift GELDAs would provide us with a natural and inherent explanation for the origin of the apparent tension between observations and theoretical models in the number density of bright galaxies at z ≳ 9.
The paper « CEERS: Forging the First Dust Grains in the Universe? A Population of Galaxies with spectroscopically-derived Extremely Low Dust Attenuation (GELDA) at 4.0<z<11.4 » is available at this link.
Learn about it in a short video:
Contact: Denis Burgarella
