Understanding the escape of Lyman continuum (LyC) and Lyα photons from giant molecular clouds (GMCs) is crucial if we are to study the reionization of the universe and to interpret spectra of observed galaxies at high redshift. To this end, we perform high-resolution, radiation-magnetohydrodynamic simulations of GMCs with self-consistent star formation and stellar feedback. We find that a significant fraction (15%-70%) of ionizing radiation escapes from the simulated GMCs with different masses (105 and 106 M o˙), as the clouds are dispersed within about 2-5 Myr from the onset of star formation. The fraction of LyC photons leaked is larger when the GMCs are less massive, metal poor, less turbulent, and less dense. The most efficient leakage of LyC radiation occurs when the total star formation efficiency of a GMC is about 20%. The escape of Lyα shows a trend similar to that of LyC photons, except that the fraction of Lyα photons escaping from the GMCs is larger ( fLyα≈f9000.27 ) and that a GMC with strong turbulence shows larger f Lyα . The simulated GMCs show a characteristic velocity separation of Δv ≈ 120 km s-1 in the time-averaged emergent Lyα spectra, suggesting that Lyα could be useful to infer the kinematics of the interstellar and circumgalactic medium. We show that Lyα luminosities are a useful indicator of the LyC escape, provided the number of LyC photons can be deduced through stellar population modeling. Finally, we find that the correlations between the escape fractions of Lyα, ultraviolet photons at 1500 Å, and the Balmer α line are weak.
Bibliographical noteFunding Information:
We thank an anonymous referee for helpful comments on the manuscript. T.K. was supported by the National Research Foundation of Korea (NRF-2019K2A9A1A06091377 and 2020R1C1C1007079). S.G. acknowledges support from a NOVA grant for the theory of massive star formation. T.G. is supported by the ERC Starting grant 757258 “TRIPLE.” This work was supported by the Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES. We additionally acknowledge support and computational resources from the Common Computing Facility (CCF) of the LABEX Lyon Institute of Origins (ANR-10-LABX-66). The supercomputing time for numerical simulations was kindly provided by KISTI (KSC-2019-CRE-0196), and large data transfer was supported by KREONET, which is managed and operated by KISTI. This work also used the DiRAC Complexity system, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility ( www.dirac.ac.uk ). Some of the simulations in this paper were performed on the Dutch National Supercomputing cluster Cartesius at SURFsara and on the Draco cluster hosted by the Max Planck Computing and Data Facility ( http://www.mpcdf.mpg.de/ ). The authors gratefully acknowledge the data storage service SDS@hd supported by the Ministry of Science, Research and the Arts Baden-Württemberg (MWK) and the German Research Foundation (DFG) through grant INST35/1314-1FUGG.
© 2022. The Author(s). Published by the American Astronomical Society.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science