Levels Of Metal Enrichment Research Articles

Metal and dust evolution in ALMA REBELS galaxies: insights for future JWST observations

ABSTRACT Atacama Large Millimeter/submillimeter Array (ALMA) observations revealed the presence of significant amounts of dust in the first Gyr of Cosmic time. However, the metal and dust build-up picture remains very uncertain due to the lack of constraints on metallicity. JWST has started to reveal the metal content of high-redshift targets, which may lead to firmer constraints on high-redshift dusty galaxies evolution. In this work, we use detailed chemical and dust evolution models to explore the evolution of galaxies within the ALMA Reionization Era Bright Emission Line Survey (REBELS) survey, testing different metallicity scenarios that could be inferred from JWST observations. In the models, we track the build-up of stellar mass using non-parametric star formation histories for REBELS galaxies. Different scenarios for metal and dust evolution are simulated by allowing different prescriptions for gas flows and dust processes. The model outputs are compared with measured dust scaling relations, by employing metallicity-dependent calibrations for the gas mass based on the [C ii] 158 μm line. Independently of the galaxies metal content, we found no need for extreme dust prescriptions to explain the dust masses revealed by ALMA. However, different levels of metal enrichment will lead to different dominant dust production mechanisms, with stardust production dominant over other interstellar medium dust processes only in the metal-poor case. This points out how metallicity measurements from JWST will significantly improve our understanding of the dust build-up in high-redshift galaxies. We also show that models struggle to reproduce observables such as dust-to-gas and dust-to-stellar ratios simultaneously, possibly indicating an overestimation of the gas mass through current calibrations, especially at high metallicities.

Prospects of the “WSO-UV” Project for Star Formation Study in Nearby Dwarf Galaxies

In the present work we consider the questions of star formation and evolution of nearby dwarf galaxies. We describe the method of star formation history determination based on multicolor photometry of resolved stars and models of color-magnitude diagrams of the galaxies. We present the results of star formation rate determination and its dependence on age and metallicity for dwarf irregular and dwarf spheroidal galaxies in the two nearby galaxy groups M81 and Cen A. Similar age of the last episode of star formation in the central part of the M81 group and also unusually high level of metal enrichment in the several galaxies of the Cen A group are mentioned. We pay special attention to the consideration of perspectives of star formation study in nearby dwarf galaxies with he new WSO-UV observatory.

Star Formation at Very Low Metallicity. II. On the Insignificance of Metal‐Line Cooling During the Early Stages of Gravitational Collapse

We study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in small protogalactic halos using three-dimensional, smoothed particle hydrodynamics simulations. Our initial conditions represent protogalaxies forming within a "fossil" H II region, a previously ionized H II region which has not yet had time to cool and recombine. Prior to cosmological reionization, such regions should be relatively common, since the characteristic lifetimes of the likely ionizing sources are significantly shorter than a Hubble time. We show that in these regions, H2 is the dominant and most effective coolant, and that it is the amount of H2 formed that determines whether or not the gas can collapse and form stars. At the low metallicities (Z < 10-3 Z☉) thought to be associated with the transition from Population III to early Population II star formation, metal-line cooling has an almost negligible effect on the evolution of low-density gas, altering the density and temperature evolution of the gas by less than 1% compared to the metal-free case at densities below 1 cm-3 and temperatures above 2000 K. Although there is evidence that metal-line cooling becomes more effective at higher density, we find no significant differences in behavior from the metal-free case at any density below our sink particle creation threshold at n = 500 cm-3. Increasing the metallicity also increases the importance of metal-line cooling, but it does not significantly affect the dynamical evolution of the low-density gas until Z ~ 0.1 Z☉. This result holds regardless of whether or not an ultraviolet background is present.

Application of Ultraclean Sampling and Analytical Techniques to an Investigation of the Impact of Power-Plant Derived Heavy Metals on Groundwater, Riverwater, Bottom Sediments and Benthic Organisms

As utility companies refit their oil-fired power stations for use with coal, they are attracting the attention of a concerned public. It becomes especially important, when operating under such close scrutiny, to conduct thoughtful environmental investigations with accurate analytic techniques. In one case, at a Massachusetts, U.S.A., power station, the routine trace metal analyses provided by private water-quality laboratories gave the impression that metal levels in stream and groundwaters adjacent to the plant were alarmingly high. This data, released by the utility company itself, resulted in extensive public criticism and costly effort for the utility and State of Massachusetts regulatory agencies. The problem, however, was more perceived than real, as the present study, conducted later, showed. This investigation brought together ultra-clean sampling and handling techniques (borrowed from geochemical oceanographic practices) and interpretive concepts from aquatic geochemistry. Levels of metal enrichment in stream waters were revealed to be in fact much lower (eg. Cu, 2 µg/l) than implied by the evidently investigator-contaminated samples (eg. Cu, 20 µg/l) from previous work, underlining the importance of employing difficult but uncompromising procedures when dealing with metals in the aquatic environment. Furthermore, with accurate analyses at hand, the geochemist's “mixing diagram” concept allowed interpretation of the fate of the power-plant derived excess metals in the cooling-water discharge; excess dissolved copper, for instance, disappeared not due to reactions with particles, but rather due to simple and rapid dilution in the effluent-river mixing zone. Examination of the relationships between various trace metal concentrations and parameters reflecting major processes controlling metal distributions (sediment grain size, labile iron and manganese concentrations) for bottom sediments from the adjacent Connecticut River revealed that natural processes largely explained the distribution of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn associated with the acid leachable fraction of the sediments in all locations. While no anomalous metal concentrations were recognized amongst sediments, oligochaete worms living in the sediments beneath the cooling-water plume appeared to have accumulated more metal than those elsewhere. Because tissue metal levels were unrelated to sediment metal levels, it seems that the worms may respond more to the dissolved metal load than to the sediment burden. Tight correlations are evident between metal concentrations determined by the author's techniques and a measure of the redox poise (COD) in groundwaters near fly ash settling ponds. Relationships between parameters determined by the routine water-qua1ity laboratories on duplicate samples, on the other hand, are characterized by the lack of correlations, suggesting that in the latter case sample handling methods were inappropriate, leading to unrepresentative concentration estimates. The correlations that appeared with the author's data, however, indicate that metal levels in the groundwater are controlled more by spatial variations in the redox poise than by pollutant (leachate) source strength.