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No matter how quiet and pristine a cave setting may appear, all speleothems contain assemblages of magnetic minerals. These iron oxide minerals are derived largely from overlying soils, though minor fractions may come from the residuum of dissolved bedrock, reworked sediment carried by episodic floods, geomicrobiological activity, and even windblown dust. Regardless of their origin, these minerals become aligned with Earth’s ambient magnetic field before they are fixed within a speleothem’s growing carbonate matrix. Here, we describe how the magnetism of stalagmites and flowstone can be used to chronicle high-resolution geomagnetic behavior and environmental change.more » « less
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Abstract We investigate the effect of dark stars (DSs) on the reionization history of the universe, and the interplay between them and feedback due to Lyman–Werner (LW) radiation in reducing the cosmic microwave background (CMB) optical depth to a value within the τ = 0.054 ± 0.007 range measured by Planck. We use a semianalytic approach to evaluate reionization histories and CMB optical depths, which includes Population II stars in atomic cooling halos and Population III stars in minihalos with LW feedback, preceded by a DS phase. We show that while LW feedback by itself can reduce the integrated optical depth to the last scattering surface to ∼0.05 only if the Population III star formation efficiency is less than ∼0.2%, the inclusion of a population of DSs can naturally lead to the measured CMB optical depth for much larger Population III star formation efficiencies ≳1%.more » « less
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ABSTRACT Using high-resolution cosmological radiation-hydrodynamic (RHD) simulations (thesan-hr), we explore the impact of alternative dark matter (altDM) models on galaxies during the Epoch of Reionization. The simulations adopt the IllustrisTNG galaxy formation model. We focus on altDM models that exhibit small-scale suppression of the matter power spectrum, namely warm dark matter (WDM), fuzzy dark matter (FDM), and interacting dark matter (IDM) with strong dark acoustic oscillations (sDAO). In altDM scenarios, both the halo mass functions and the ultraviolet luminosity functions at z ≳ 6 are suppressed at the low-mass/faint end, leading to delayed global star formation and reionization histories. However, strong non-linear effects enable altDM models to ‘catch up’ with cold dark matter (CDM) in terms of star formation and reionization. The specific star formation rates are enhanced in halos below the half-power mass in altDM models. This enhancement coincides with increased gas abundance, reduced gas depletion times, more compact galaxy sizes, and steeper metallicity gradients at the outskirts of the galaxies. These changes in galaxy properties can help disentangle altDM signatures from a range of astrophysical uncertainties. Meanwhile, it is the first time that altDM models have been studied in RHD simulations of galaxy formation. We uncover significant systematic uncertainties in reionization assumptions on the faint-end luminosity function. This underscores the necessity of accurately modeling the small-scale morphology of reionization in making predictions for the low-mass galaxy population. Upcoming James Webb Space Telescope imaging surveys of deep lensed fields hold potential for uncovering the faint low-mass galaxy population, which could provide constraints on altDM models.