Abstract
Context. Resonant lines are powerful probes of the interstellar and circumgalactic medium of galaxies. Their transfer in gas being a complex process, the interpretation of their observational signatures, either in absorption or in emission, is often not straightforward. Numerical radiative transfer simulations are needed to accurately describe the travel of resonant line photons in real and in frequency space, and to produce realistic mock observations. Aims. This paper introduces RASCAS, a new public 3D radiative transfer code developed to perform the propagation of any resonant line in numerical simulations of astrophysical objects. RASCAS was designed to be easily customisable and to process simulations of arbitrarily large sizes on large supercomputers. Methods. RASCAS performs radiative transfer on an adaptive mesh with an octree structure using the Monte Carlo technique. RASCAS features full MPI parallelisation, domain decomposition, adaptive load-balancing, and a standard peeling algorithm to construct mock observations. The radiative transport of resonant line photons through different mixes of species (e.g. H I, Si II, Mg II, Fe II), including their interaction with dust, is implemented in a modular fashion to allow new transitions to be easily added to the code. Results. RASCAS is very accurate and efficient. It shows perfect scaling up to a minimum of a thousand cores. It has been fully tested against radiative transfer problems with analytic solutions and against various test cases proposed in the literature. Although it was designed to describe accurately the many scatterings of line photons, RASCAS may also be used to propagate photons at any wavelength (e.g. stellar continuum or fluorescent lines), or to cast millions of rays to integrate the optical depths of ionising photons, making it highly versatile.
Highlights
Resonant lines are very powerful tracers of the interstellar medium (ISM) and the circumgalactic medium (CGM) of galaxies: their spectral and spatial distributions imprint the kinematics and the geometry of the gas in which they scatter
An example here is the interpretation of diffuse Lyman-α emission seen in deep narrow-band stacks (e.g. Steidel et al 2011; Momose et al 2014) or in VLT/MUSE datacubes (Wisotzki et al 2016; Leclercq et al 2017) in relation with the multi-band photometry from Hubble Space Telescope (HST). The interpretation of these phenomena requires selfconsistent multi-wavelength mocks that include the full radiative transfer (RT) effects due to Lyman-α scattering and dust extinction. Another example is the very difficult interpretation of absorption lines in galaxy spectra because observations cannot tell us whether they are due to the ISM or CGM
This paper presents a new 3D RT code, RAdiation SCattering in Astrophysical Simulations (RASCAS), which was designed to construct accurate multi-wavelength mock observations from high-resolution simulations
Summary
Resonant lines are very powerful tracers of the interstellar medium (ISM) and the circumgalactic medium (CGM) of galaxies: their spectral and spatial distributions imprint the kinematics and the geometry of the gas in which they scatter. The interpretation of these phenomena requires selfconsistent multi-wavelength mocks that include the full radiative transfer (RT) effects due to Lyman-α scattering and dust extinction Another example is the very difficult interpretation of absorption lines in galaxy spectra because observations cannot tell us whether they are due to the ISM or CGM. This may be provided by the simulation code, as is the case for H and He with ramses-rt (Rosdahl et al 2013), or it may be necessary to post-process the simulation to estimate the emissivities of the gas This first step is very simulation- and model-dependent, and RASCAS chooses to encapsulate it in a simulation-plugin module and to implement two stand-alone pre-processing codes which generate an adaptive mesh with all the needed physical information about the gaseous medium, and the initial conditions for light emission in the form of lists of photon packets.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
