Research

ΛCDM is the leading cosmological model and accurately describes many observed phenomena in the universe, including the large-scale distribution of galaxies, fluctuations in the cosmic microwave background (CMB), and the universe's accelerated expansion. In this six-parameter model, initial fluctuations in the dark matter density collapse gravitationally into dark matter halos, in which galaxies form. Though this picture is largely successful at describing our observed universe, there are many open questions, including the formation of the earliest galaxies, the nature of dark matter, what structure looks like on small scales, and the origin of the tension of cosmological parameters between late and early measurements.

l model structure formation in the Universe — from galaxy surveys that trace the large-scale structure at the Epoch of Reionization (e.g., Drakos et al., 2022b) to small satellite galaxies that are sensitive to the nature of dark matter (e.g., Drakos et al., 2017, 2020, 2022a, 2023), to galaxy clusters that carry imprints of the growth history of the Universe (e.g., Drakos et al., 2019a,b; Amoura et al., 2021, 2023) — to address key questions about galaxy formation, the nature of dark matter, and cosmology.

  • The High-Redshift Universe

    The Epoch of Reionization (EoR; 6 < z < 10) is one of the least constrained periods in the Universe’s history, and there are many open questions about the timeline, sources, and topology of the EoR. Thanks to new surveys such JWST’s COSMOS-Web Survey (Casey et al., 2023) and deep fields with Roman Space Telescope, we will soon understand much more about this epoch.

    Mock galaxy catalogs are important for designing surveys, analyzing data, and scientific interpretation. I created the Deep Realistic Extragalactic Model (DREaM) to create synthetic galaxy catalogs for deep and wide galaxy surveys. I used this model to explore the scientific returns of an ultra-deep field with Roman (Drakos et al., 2022), and also to for COSMOS-Web (Drakos et al. in prep).

  • Substructure Evolution

    Dark matter substructure may be one of the best places to test for the nature of dark matter. Since the dense centres of subhalos are difficult to resolve in simulations, a theoretical understanding of subhalo evolution is required.

    I developed the energy-truncation model to predict the evolution of dwarf galaxies beyond the regimes resolved in simulations (Drakos et al. 2017, 2020, 2022). This work implies that model assumption can make an order-of-magnitude difference in the predicted dark matter annihilation rate (Drakos et al., 2023).

  • Cosmological Parameters

    The growing tension between cosmological parameters H0 and σ8 inferred from large-scale-structure (LSS) measurements and the CMB may indicate there needs to be serious revisions to the concordance cosmological model. However, to determine whether these tensions are real and not due to unknown systematics, we need independent tests for measuring H0 and σ8.

    Many local probes of H0 are dominated by errors in model-dependent peculiar velocity measurements. I am currently eploring how model assumptions affect these measurements.

    Further, since galaxy clusters form within the largest dark matter halos, galaxy cluster properties can be used as a tracer of assembly time and thus to constrain σ8. I am working with a team of researchers on how to use cluster assembly times as a cosmological test ( Drakos et al. 2019a, 2019b, Amoura et al. 2021, 2022)