The physical origins and dominant emission mechanisms of Lyman alpha haloes: results from the TNG50 simulation in comparison to MUSE observations

Abstract

Extended Lyman-alpha emission is now commonly detected around high redshift galaxies through stacking and even on individual basis. Despite recent observational advances, the physical origin of these Lyman-alpha halos (LAHs), as well as their relationships to galaxies, quasars, circumgalactic gas, and other environmental factors remains unclear. We present results from our new Lyman-alpha full radiative transfer code voroILTIS which runs directly on the unstructured Voronoi tessellation of cosmological hydrodynamical simulations. We make use of the TNG50 simulation and simulate LAHs from redshift z = 2 to z = 5, focusing on star-forming galaxies with $8.0 < \log _{10}{(M_\star /\rm {M}_\odot )} < 10.5$. While TNG50 does not directly follow ionizing radiation, it includes an on-the-fly treatment for active galactic nuclei and ultraviolet background radiation with self-shielding, which are important processes impacting the cooling and ionization of the gas. Based on this model, we present the predictions for the stacked radial surface brightness profiles of Lyα as a function of galaxy mass and redshift. Comparison with data from the MUSE UDF at z > 3 reveals a promising level of agreement. We measure the correlations of LAH size and central brightness with galaxy properties, finding that at the masses of $8.5 \le \log _{10} \left(M_\star /\rm {M}_\odot \right) \le 9.5$, physical LAH sizes roughly double from z = 2 to z = 5. Finally, we decompose the profiles into contributions from diffuse emission and scattered photons from star-forming regions. In our simulations, we find rescattered photons from star-forming regions to be the major source in observed LAHs. Unexpectedly, we find that the flattening of LAH profiles at large radii becomes dominated by photons originating from other nearby halos rather than diffuse emission itself.

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

“…Another way uses hydrodynamical simulations that resolve the gas around galaxies, which can be postprocessed with a Monte Carlo radiative transfer calculation to predict the shape of Lyα emission around galaxies (e.g., Lake et al 2015;Kimock et al 2021;Mitchell et al 2021). 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).…”

“…Comparisons of predictions with measurements draw different conclusions. While Steidel et al (2011), Gronke &Bird (2017), andByrohl et al (2021) find that most of the extended Lyα emission can be explained by scattering of Lyα photons from the central galaxy or nearby galaxies, Lake et al (2015) stressed the importance of cooling radiation in producing Lyα halos when they compared their simulation with observations from Momose et al (2014). Mitchell et al (2021) report that satellite galaxies are the predominant source of Lyα photons at 10-40 kpc, while cooling radiation also plays a relevant role.…”

“…Because the dominant origin of the Lyα halo photons depends on, among other things, the distance to the galaxies (Byrohl et al 2021;Mitchell et al 2021), observations of Lyα profiles out to larger distances will be helpful. An ideal data set for this is provided by the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX; Hill et al 2008;Gebhardt et al 2021;Hill et al 2021), which is designed to detect more than one million LAEs at redshifts 1.9 < z < 3.5 in a 10.9 Gpc 3 volume to measure their clustering and thereby constrain cosmological parameters.…”

Cool circumgalactic gas in galaxy clusters: connecting the DESI legacy imaging survey and SDSS DR16 MgII absorbers

“…The complex interplay between gas inflows and outflows powered by supernova explosions or accreting black holes is known as the cosmic baryon cycle, and is a key ingredient to understanding galaxy formation and evolution (see Tumlinson et al 2017;Péroux & Howk 2020, for reviews). Both observations (Stocke et al 2013;Zhu et al 2014;Lan & Mo 2018;Zahedy et al 2019;Tchernyshyov et al 2021) and simulations (Oppenheimer et al 2018;Peeples et al 2019;Fielding et al 2020;Nelson et al 2020;Byrohl et al 2021) have revealed that the CGM is multi-phase and hosts gas with a wide range of temperatures and densities.…”

AGN-driven outflows and the formation of Ly$α$ nebulae around high-z quasars

“…While multiple cosmological simulations have by now succeeded in reproducing the estimated masses of supermassive black holes at 𝑧 > 6, no attempt has been made to predict their associated extended Ly𝛼 emission with such simulations. Studies have begun to employ cosmological simulations to pin down the origin of extended Ly𝛼 emission, but these have mostly concentrated on massive haloes at 𝑧 ≈ 2 (Rosdahl & Blaizot 2012;Cantalupo et al 2014;Gronke & Bird 2017) or lower mass haloes (Smith et al 2019;Mitchell et al 2021;Byrohl et al 2021), in all cases without an on-the-fly treatment of quasar radiation.…”