Effects of Spatial Discretization in Lyα Line Radiation Transfer Simulations

Camps, Peter; Behrens, Christoph; Baes, M.; Kapoor, Anand Utsav; Grand, Robert J. J.

doi:10.3847/1538-4357/ac06cb

“…- The dust benchmarks were run with forced scattering and the Lyman-α benchmarks without forced scattering. All results are within the uncertainty levels noted in previous work Camps et al 2021). Even if all materials in these benchmark models have non-negative cross sections, we can still conclude that the explicit absorption technique is very robust, at least in this regime.…”

Section: Published Benchmarkssupporting

confidence: 80%

“…In previous work, we employed several benchmark problems that have been published in the literature to test SKIRT with dust media ) and for Lyman-α line transfer (Camps et al 2021). For the current work, to verify our updated implementation, we ran the benchmark problems listed below with explicit absorption enabled.…”

Section: Published Benchmarksmentioning

confidence: 99%

Monte Carlo radiative transfer with explicit absorption to simulate absorption, scattering, and stimulated emission

Baes

¹

,

Camps

²

,

Matsumoto

³

2022

A&A

Self Cite

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Context. The Monte Carlo method is probably the most widely used approach to solve the radiative transfer problem, especially in a general 3D geometry. The physical processes of emission, absorption, and scattering are easily incorporated in the Monte Carlo framework. Net stimulated emission, or absorption with a negative cross section, does not fit this method, however. Aims. We explore alterations to the standard photon packet life cycle in Monte Carlo radiative transfer that allow the treatment of net stimulated emission without loss of generality or efficiency. Methods. We present the explicit absorption technique that allows net stimulated emission to be handled efficiently. It uses the scattering rather than the extinction optical depth along a photon packet's path to randomly select the next interaction location, and offers a separate, deterministic treatment of absorption. We implemented the technique in a special-purpose Monte Carlo code for a two-stream 1D radiative transfer problem and in the fully featured 3D code SKIRT, and we studied its overall performance using quantitative statistical tests. Results. Our special-purpose code is capable of recovering the analytical solutions to the two-stream problem in all regimes, including the one of strong net stimulated emission. The implementation in SKIRT is straightforward, as the explicit absorption technique easily combines with the variance reduction and acceleration techniques already incorporated. In general, explicit absorption tends to improve the efficiency of the Monte Carlo routine in the regime of net absorption. Conclusions. Explicit absorption allows the treatment of net stimulated emission in Monte Carlo radiative transfer, it interfaces smoothly with other variance reduction and acceleration techniques, and it tends to improve the efficiency of the simulations in the net absorption regime. We recommend to always include this new technique in Monte Carlo radiative transfer.

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“…Both the spectral profiles and emergent luminosities are expected to change for a simulation of both lower and higher resolution (e.g. Camps et al 2021). Correctly modelling the ISM is key for accurately modelling emission lines and thus it is important to consider that any issues with the ISM model in SPHINX will lead to systematic biases in our results.…”

Section: Caveatsmentioning

confidence: 99%

Mg ii in the JWST era: a probe of Lyman continuum escape?

Katz

¹

,

Garel

²

,

Rosdahl

³

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Limited constraints on the evolution of the Lyman Continuum (LyC) escape fraction represent one of the primary uncertainties in the theoretical determination of the reionization history. Due to the intervening intergalactic medium (IGM), the possibility of observing LyC photons directly in the epoch of reionization is highly unlikely. For this reason, multiple indirect probes of LyC escape have been identified, some of which are used to identify low-redshift LyC leakers (e.g. O32), while others are primarily useful at z > 6 (e.g. [O III]/[C III] far-infrared emission). The flux ratio of the resonant Mg II doublet emission at 2796Å and 2803Å as well as the Mg II optical depth have recently been proposed as ideal diagnostics of LyC leakage that can be employed at z > 6 with JWST. Using state-of-the-art cosmological radiation hydrodynamics simulations post-processed with CLOUDY and resonant-line radiative transfer, we test whether Mg II is indeed a useful probe of LyC leakage. Our simulations indicate that the majority of bright, star-forming galaxies with high LyC escape fractions are expected to be Mg II emitters rather than absorbers at z = 6. However, we find that the Mg II doublet flux ratio is a more sensitive indicator of dust rather than neutral hydrogen, limiting its use as a LyC leakage indicator to only galaxies in the optically thin regime. Given its resonant nature, we show that Mg II will be an exciting probe of the complex kinematics in high-redshift galaxies in upcoming JWST observations.

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“…Most of these models simulate small numbers of galaxies, while Zheng et al (2011), Gronke &Bird (2017), andByrohl et al (2021) calculate Lyα radiative transfer in cosmological hydrodynamical simulations and offer predictions for large samples of galaxies. While being a promising tool, hydrodynamical simulations of galaxy formation in cosmological volumes with subkiloparsec resolutions (e.g., Nelson et al 2020) possibly suffer from convergence issues both in the physical gas state (e.g., van de Voort et al 2019) and in Lyα radiative transfer (e.g., Camps et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Surface Brightness Profile of Lyman-α Halos out to 320 kpc in HETDEX

Niemeyer

¹

,

Komatsu

²

,

Byrohl

³

et al. 2022

ApJ

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We present the median-stacked Lyman-α (Lyα) surface brightness profiles of 968 spectroscopically selected Lyα emitting galaxies (LAEs) at redshifts 1.9 < z < 3.5 in the early data of the Hobby-Eberly Telescope Dark Energy Experiment. The selected LAEs are high-confidence Lyα detections with high signal-to-noise ratios observed with good seeing conditions (point-spread function FWHM <1.″4), excluding active galactic nuclei. The Lyα luminosities of the LAEs are 1042.4–1043 erg s−1. We detect faint emission in the median-stacked radial profiles at the level of ( 3.6 ± 1.3 ) × 10 − 20 erg s − 1 cm − 2 arcsec − 2 from the surrounding Lyα halos out to r ≃ 160 kpc (physical). The shape of the median-stacked radial profile is consistent at r < 80 kpc with that of much fainter LAEs at 3 < z < 4 observed with the Multi Unit Spectroscopic Explorer (MUSE), indicating that the median-stacked Lyα profiles have similar shapes at redshifts 2 < z < 4 and across a factor of 10 in Lyα luminosity. While we agree with the results from the MUSE sample at r < 80 kpc, we extend the profile over a factor of two in radius. At r > 80 kpc, our profile is flatter than the MUSE model. The measured profile agrees at most radii with that of galaxies in the Byrohl et al. cosmological radiative transfer simulation at z = 3. This suggests that the surface brightness of a Lyα halo at r ≲ 100 kpc is dominated by resonant scattering of Lyα photons from star-forming regions in the central galaxy, whereas at r > 100 kpc, it is dominated by photons from galaxies in surrounding dark matter halos.

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Effects of Spatial Discretization in Lyα Line Radiation Transfer Simulations

Cited by 18 publications

References 82 publications

Monte Carlo radiative transfer with explicit absorption to simulate absorption, scattering, and stimulated emission

Monte Carlo radiative transfer with explicit absorption to simulate absorption, scattering, and stimulated emission

Mg ii in the JWST era: a probe of Lyman continuum escape?

Surface Brightness Profile of Lyman-α Halos out to 320 kpc in HETDEX

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