First insights into the ISM at z > 8 with JWST : possible physical implications of a high [O iii ] λ4363/[O iii ] λ5007
Two modes of LyC escape from bursty star formation: implications for [C II] deficits and the sources of reionization
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 fesc>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 M1500Å 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 fesc>20 per cent dominate the ionizing photon budget at z ≳ 7.5 but the contribution from galaxies with fesc<5 per cent becomes significant at the tail-end of reionization.
Strong C iv emission from star-forming galaxies: a case for high Lyman continuum photon escape
Impact of radiation feedback on the formation of globular cluster candidates during cloud–cloud collisions
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 MGC ∼ 105 M⊙ forms within ≈3 Myr when two GMCs with mass MGMC = 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.