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ABSTRACT Atomic hydrogen (H i) serves a crucial role in connecting galactic-scale properties such as star formation with the large-scale structure of the Universe. While recent numerical simulations have successfully matched the observed covering fraction of H i near Lyman Break Galaxies (LBGs) and in the foreground of luminous quasars at redshifts $$z \lesssim 3$$, the low-mass end remains as-of-yet unexplored in observational and computational surveys. We employ a cosmological, hydrodynamical simulation (FIREbox) supplemented with zoom-in simulations (MassiveFIRE) from the Feedback In Realistic Environments (FIRE) project to investigate the H i covering fraction of Lyman Limit Systems ($$N_{{\text{H}}\, \rm{{\small I}}} \gtrsim 10^{17.2}$$ cm$$^{-2}$$) across a wide range of redshifts ($z=0-6$) and halo masses ($$10^8-10^{13} \, \,\mathrm{ M}_{\odot }$$ at $z=0$, $$10^8-10^{11}\, \,\mathrm{ M}_{\odot }$$ at $z=6$) in the absence of feedback from active galactic nuclei. We find that the covering fraction inside haloes exhibits a strong increase with redshift, with only a weak dependence on halo mass for higher mass haloes. For massive haloes ($$M_{\mathrm{vir}} \sim 10^{11}-10^{12} \,\mathrm{ M}_{\odot }$$), the radial profiles showcase scale-invariance and remain independent of mass. The radial dependence is well captured by a fitting function. The covering fractions in our simulations are in good agreement with measurements of the covering fraction in LBGs. Our comprehensive analysis unveils a complex dependence with redshift and halo mass for haloes with $$M_{\mathrm{vir}} \lesssim 10^{10} \,\mathrm{ M}_{\odot }$$ that future observations aim to constrain, providing key insights into the physics of structure formation and gas assembly.
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The ASTRID simulation: galaxy formation and reionization
ABSTRACT We introduce the Astrid simulation, a large-scale cosmological hydrodynamic simulation in a $$250 \, h^{-1}\mathrm{Mpc}$$ box with 2 × 55003 particles. Astrid contains a large number of high redshift galaxies, which can be compared to future survey data, and resolves galaxies in haloes more massive than $$2\times 10^9 \, \mathrm{M}_{\odot }$$. Astrid has been run from z = 99 to 3. As a particular focus is modelling the high redshift Universe, it contains models for inhomogeneous hydrogen and helium reionization, baryon relative velocities and massive neutrinos, as well as supernova and AGN feedback. The black hole model includes mergers driven by dynamical friction rather than repositioning. We briefly summarize the implemented models, and the technical choices we took when developing the simulation code. We validate the model, showing good agreement with observed ultraviolet luminosity functions, galaxy stellar mass functions and specific star formation rates (SFRs). We show that the redshift at which a given galaxy underwent hydrogen reionization has a large effect on the halo gas fraction. Finally, at z = 6, haloes with $$M \sim 2\times 10^9 \, \mathrm{M}_{\odot }$$ which have been reionized have an SFR 1.5 times greater than those which have not yet been reionized.
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- Award ID(s):
- 1817256
- PAR ID:
- 10365881
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 512
- Issue:
- 3
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 3703-3716
- Size(s):
- p. 3703-3716
- Sponsoring Org:
- National Science Foundation
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