Adrianne Slyz

Abstract:

We use the SPHINX²⁰ cosmological radiation hydrodynamics simulation to study how Lyman continuum (LyC) photons escape from galaxies and the observational signatures of this escape. We define two classes of LyC leaker: Bursty Leakers and Remnant Leakers, based on their star formation rates (SFRs) that are averaged over 10 Myr (SFR₁₀) or 100 Myr (SFR₁₀₀). Both have f_esc>20 per cent and experienced an extreme burst of star formation, but Bursty Leakers have SFR₁₀ > SFR₁₀₀, while Remnant Leakers have SFR₁₀ < SFR₁₀₀. The maximum SFRs in these bursts were typically ∼100 times greater than the SFR of the galaxy prior to the burst, a rare 2σ outlier among the general high-redshift galaxy population. Bursty Leakers are qualitatively similar to ionization-bounded nebulae with holes, exhibiting high ionization parameters and typical H II region gas densities. Remnant Leakers show properties of density-bounded nebulae, having normal ionization parameters but much lower H II region densities. Both types of leaker exhibit [C II]_158μm deficits on the [C II]–SFR₁₀₀ relation, while only Bursty Leakers show deficits when ₁₀ is used. We predict that [C II] luminosity and SFR indicators such as Hα and M_1500Å can be combined to identify both types of LyC leaker and the mode by which photons are escaping. These predictions can be tested with [C II] observations of known z = 3–4 LyC leakers. Finally, we show that leakers with f_esc>20 per cent dominate the ionizing photon budget at z ≳ 7.5 but the contribution from galaxies with f_esc<5 per cent becomes significant at the tail-end of reionization.

Abstract:

Cosmological N-body simulations of the dark matter component of the universe typically use initial conditions with a fixed power spectrum and random phases of the density field, leading to structure consistent with the local distribution of galaxies only in a statistical sense. It is, however, possible to infer the initial phases which lead to the configuration of galaxies and clusters that we see around us. We analyse the CSiBORG suite of 101 simulations, formed by constraining the density field within 155 Mpc h⁻¹ with dark matter particle mass 4.38 × 10⁹ M_⊙, to quantify the degree to which constraints imposed on 2.65 Mpc h⁻¹ scales reduce variance in the halo mass function and halo–halo cross-correlation function on a range of scales. This is achieved by contrasting CSiBORG with a subset of the unconstrained Quijote simulations and expectations for the ΛCDM average. Using the FOF, PHEW, and HOP halofinders, we show that the CSiBORG suite beats cosmic variance at large mass scales (≳10¹⁴ M_⊙ h⁻¹), which are most strongly constrained by the initial conditions, and exhibits a significant halo–halo cross-correlation out to ∼30 Mpc h⁻¹. Moreover, the effect of the constraints percolates down to lower mass objects and to scales below those on which they are imposed. Finally, we develop an algorithm to ‘twin’ haloes between realizations and show that approximately 50 per cent of haloes with mass greater than 10¹⁵ M_⊙ h⁻¹ can be identified in all realizations of the CSiBORG suite. We make the CSiBORG halo catalogues publicly available for future applications requiring knowledge of the local halo field.

Abstract:

To understand the impact of radiation feedback during the formation of a globular cluster (GC), we simulate a head-on collision of two turbulent giant molecular clouds (GMCs). A series of idealized radiation-hydrodynamic simulations is performed, with and without stellar radiation or Type II supernovae. We find that a gravitationally bound, compact star cluster of mass M_GC ∼ 10⁵ M_⊙ forms within ≈3 Myr when two GMCs with mass M_GMC = 3.6 × 10⁵ M⊙ collide. The GC candidate does not form during a single collapsing event but emerges due to the mergers of local dense gas clumps and gas accretion. The momentum transfer due to the absorption of the ionizing radiation is the dominant feedback process that suppresses the gas collapse, and photoionization becomes efficient once a sufficient number of stars form. The cluster mass is larger by a factor of ∼2 when the radiation feedback is neglected, and the difference is slightly more pronounced (16%) when extreme Lyα feedback is considered in the fiducial run. In the simulations with radiation feedback, supernovae explode after the star-forming clouds are dispersed, and their metal ejecta are not instantaneously recycled to form stars.