Spectral reconstruction for radiation hydrodynamic simulations of galaxy evolution

Abstract

Radiation from stars and AGN plays an important role in galaxy formation and evolution, and profoundly transforms the IGM, CGM & ISM. On-the-fly RT has started being incorporated in cosmological simulations, but the complex, evolving radiation spectra are often crudely approximated with a small number of broad bands with piece-wise constant intensity and a fixed photo-ionisation cross-section. Such a treatment is unable to capture the changes to the spectrum as light is absorbed while it propagates through a medium with non-zero opacity. This can lead to large errors in photo-ionisation and heating rates. We present a novel approach of discretising the radiation field in narrow bands, located at the edges of the typically used bands, in order to capture the power-law slope of the radiation field. In combination with power-law approximations for the photo-ionisation cross-sections, this model allows us to self-consistently combine radiation from sources with different spectra and accurately follow the ionisation states of primordial and metal species through time. The method is implemented in Gasoline2 in connection with Trevr2. We compare our new piece-wise power-law reconstruction to the piece-wise constant method in calculating the primordial chemistry photo-ionisation and heating rates under an evolving UVB and stellar spectrum, and find that our method reduces errors significantly, up to two orders of magnitude in the case of HeII ionisation. We apply our new spectral reconstruction method in RT post-processing of a cosmological zoom-in simulation, including radiation from stars and a live UVB, and find a significant increase in total neutral hydrogen mass in the ISM and the CGM due to shielding of the UVB and a low escape fraction of the stellar radiation. This demonstrates the importance of RT and an accurate spectral approximation in simulating the CGM-galaxy ecosystem.

Submitted for publication to A&A, 17 pages, 15 figures

References in corpus (21)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• The Circumgalactic Medium
• The effect of photo-ionization on the cooling rates of enriched, astrophysical plasmas
• Star Formation and Feedback in Smoothed Particle Hydrodynamic Simulations--I. Isolated Galaxies
• The Effects of Stellar Rotation. II. A Comprehensive Set of Starburst99 Models
• Grackle: a Chemistry and Cooling Library for Astrophysics
• Introducing the THESAN project: radiation-magnetohydrodynamic simulations of the epoch of reionization
• Cosmological Radiative Transfer Codes Comparison Project I: The Static Density Field Tests
• A Superbubble Feedback Model for Galaxy Simulations
• The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming Galaxies
• Cosmic Reionization On Computers I. Design and Calibration of Simulations
• Deep into the structure of the first galaxies: SERRA views
• Galaxies that Shine: radiation-hydrodynamical simulations of disk galaxies
• Tree-based solvers for adaptive mesh refinement code FLASH - I: gravity and optical depths
• The short ionizing photon mean free path at z=6 in Cosmic Dawn III, a new fully-coupled radiation-hydrodynamical simulation of the Epoch of Reionization
• Simulating the diversity of shapes of the Lyman-$\alpha$ line
• RAMSES-RTZ: Non-Equilibrium Metal Chemistry and Cooling Coupled to On-The-Fly Radiation Hydrodynamics
• Star Cluster Formation and Survival in the First Galaxies
• Effect of Cosmic UV Background on Star Formation in High Redshift Galaxies
• TREVR: A general $Nlo{g}^{2}N$ radiative transfer algorithm
• A comparison of numerical methods for computing the reionization of intergalacitc hydrogen and helium by a central radiating source