Taysun Kimm

In this paper, we explore the significant, non-linear impact that stellar winds have on H ii regions. We perform a parameter study using three-dimensional radiative magnetohydrodynamic simulations of wind and ultraviolet radiation feedback from a 35 M⊙ star formed self-consistently in a turbulent, self-gravitating cloud, similar to the Orion Nebula (M42) and its main ionizing source θ1 Ori C. Stellar winds suppress early radiative feedback by trapping ionizing radiation in the shell around the wind bubble. Rapid breakouts of warm photoionized gas (‘champagne flows’) still occur if the star forms close to the edge of the cloud. The impact of wind bubbles can be enhanced if we detect and remove numerical overcooling caused by shocks crossing grid cells. However, the majority of the energy in the wind bubble is still lost to turbulent mixing between the wind bubble and the gas around it. These results begin to converge if the spatial resolution at the wind bubble interface is increased by refining the grid on pressure gradients. Wind bubbles form a thin chimney close to the star, which then expands outwards as an extended plume once the wind bubble breaks out of the dense core the star formed in, allowing them to expand faster than a spherical wind bubble. We also find wind bubbles mixing completely with the photoionized gas when the H ii region breaks out of the cloud as a champagne flow, a process we term ‘hot champagne’.

The Ly α line is a powerful probe of distant galaxies, which contains information about inflowing/outflowing gas through which Ly α photons scatter. To develop our understanding of this probe, we post-process a zoom-in radiation-hydrodynamics simulation of a low-mass (Mstar ∼ 109 M⊙) galaxy to construct 22 500 mock spectra in 300 directions from z = 3 to 4. Remarkably, we show that one galaxy can reproduce the variety of a large sample of spectroscopically observed Ly α line profiles. While most mock spectra exhibit double-peak profiles with a dominant red peak, their shapes cover a large parameter space in terms of peak velocities, peak separation, and flux ratio. This diversity originates from radiative transfer effects at interstellar medium and circum-galactic medium (CGM) scales, and depends on galaxy inclination and evolutionary phase. Red-dominated lines preferentially arise in face-on directions during post-starburst outflows and are bright. Conversely, accretion phases usually yield symmetric double peaks in the edge-on direction and are fainter. While resonant scattering effects at <0.2 × Rvir are responsible for the broadening and velocity shift of the red peak, the extended CGM acts as a screen and impacts the observed peak separation. The ability of simulations to reproduce observed Ly α profiles and link their properties with galaxy physical parameters offers new perspectives to use Ly α to constrain the mechanisms that regulate galaxy formation and evolution. Notably, our study implies that deeper Ly α surveys may unveil a new population of blue-dominated lines tracing inflowing gas.

The detection of Lyα nebulae around z ≳ 6 quasars reveals extended gas reservoirs around the first rapidly growing supermassive black holes. Observations of z > 6 quasars can be explained by cosmological models provided that the black holes by which they are powered evolve in rare, massive dark matter haloes. Whether these models also explain the observed extended Lyα emission remains an open question. We post-process a suite of cosmological, radiation-hydrodynamic simulations, targeting a quasar host halo at z > 6 with the Lyα radiative transfer code Rascas. A combination of recombination radiation from photo-ionized hydrogen and emission from collisionally excited gas powers Lyα nebulae with a surface brightness profile in a close agreement with observations. We also find that, even on its own, resonant scattering of the Lyα line associated to the quasar’s broad-line region can also generate Lyα emission on $\sim 100 \, \rm kpc$ scales, resulting in comparable agreement with observed surface brightness profiles. Even if powered by a broad quasar Lyα line, Lyα nebulae have narrow line-widths $\lesssim 1000 \, \rm km \, s^{-1}$, consistent with observational constraints. Even if there is no quasar, we find that halo gas cooling produces a faint, extended Lyα glow. However, to explain the brightest Lyα nebulae, our simulations unambiguously require quasar-powered outflows to clear out the galactic nucleus and allow the Lyα flux to escape and still remain resonant with halo gas. The close match between observations and simulations with quasar outflows suggest that AGN feedback already operates before $z \, = \, 6$ and confirms that high-z quasars reside in massive haloes tracing overdensities.