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.
Complex radiative transfer (RT) of the Lyman-α photons poses a theoretical challenge to galaxy surveys which infer the large-scale structure with Lyman-α emitters (LAEs). Guided by RT simulations, prior studies investigated the impact of RT on the largescale LAE clustering, and claimed that RT induces a selection effect which results in an anisotropic distortion even in real space but in an otherwise negligible effect in redshift space. However, our previous study, which relies on a full radiative transfer code run on the Illustris simulations, shows that the anisotropic selection effect was drastically reduced with higher spatial resolution. Adopting the same simulation framework, we further study the impact of RT on the LAE clustering in redshift space. Since we measure LAE's radial position through a spectral peak of a Lyman-α emission, the frequency shift due to RT contaminates the redshift measurement and hence the inferred radial position in redshift space. We demonstrate that this additional RT offset suppresses the LAE clustering along the line of sight, which can be interpreted as a novel Fingers-of-God (FoG) effect. To assess the FoG effect, we develop a theoretical framework with particular emphasis on its connection with the underlying one-point velocity distribution which simultaneously takes into account the RT offset as well as the peculiar velocity that is commonly studied in the context of the Redshift Space Distortion (RSD). Although our findings strongly encourage a more careful RSD modeling in LAE surveys, we also seek a method to mitigate the additional FoG effect due to RT by making use of other information in a Lyman-α spectrum.
Recent Suzaku X-ray spectra of SNR 3C 397 indicate enhanced stable iron-group element abundances of Ni, Mn, Cr, and Fe. Seeking to address key questions about the progenitor and explosion mechanism of 3C 397, we compute nucleosynthetic yields from a suite of multidimensional hydrodynamics models in the near-Chandrasekhar mass, single-degenerate paradigm for supernova Type Ia. Varying the progenitor white dwarf internal structure, composition, ignition, and explosion mechanism, we find the best match to the observed iron-peak elements of 3C 397 are dense (central density ≥ 6×10 9 g cm −3 ), low-carbon white dwarfs that undergo a weak, centrally-ignited deflagration, followed by a subsequent detonation. The amount of 56 Ni produced is consistent with a normal or bright normal supernova Type Ia. A pure deflagration of a centrally-ignited, low central density ( 2×10 9 g cm −3 ) progenitor white dwarf, frequently considered in the literature, is also found to produce good agreement with 3C 397 nucleosynthetic yields, but leads to a subluminous SN Ia event, in conflict with X-ray linewidth data. Additionally, in contrast to prior work which suggested a large super-solar metallicity for the white dwarf progenitor for SNR 3C 397, we find satisfactory agreement for solar and sub-solar metallicity progenitors. We discuss a range of implications our results have for the single-degenerate channel.
We outline theoretical predictions for extended emission from MgII, tracing cool ∼104 K gas in the circumgalactic medium (CGM) of star-forming galaxies in the high-resolution TNG50 cosmological magnetohydrodynamical simulation. We synthesize surface brightness maps of this strong rest-frame ultraviolet metal emission doublet (λλ2796, 2803), adopting the assumption that the resonant scattering of MgII can be neglected and connecting to recent and upcoming observations with the Keck/KCWI, VLT/MUSE, and BlueMUSE optical integral field unit spectrographs. Studying galaxies with stellar masses 7.5 < log (M⋆/M⊙) < 11 at redshifts z = 0.3, 0.7, 1 and 2 we find that extended MgII haloes in emission, similar to their Lyα counterparts, are ubiquitous across the galaxy population. Median surface brightness profiles exceed 10−19 erg s−1 cm−2 arcsec−2 in the central ∼ 10s of kpc, and total halo MgII luminosity increases with mass for star-forming galaxies, reaching 1040 erg s−1 for M⋆ ∼ 109.5 M⊙. MgII halo sizes increase from a few kpc to ≳ 20 kpc at the highest masses, and sizes are larger for haloes in denser environments. MgII haloes are highly structured, clumpy, and asymmetric, with isophotal axial ratio increasing with galaxy mass. Similarly, the amount and distribution of MgII emission depends on the star formation activity of the central galaxy. Kinematically, inflowing versus outflowing gas dominates the MgII luminosity at high and low galaxy masses, respectively, although the majority of MgII halo emission at z ∼ 0.7 traces near-equilibrium fountain flows and gas with non-negligible rotational support, rather than rapidly outflowing galactic winds.
Context. Lyman-α emitters (LAEs) are a promising probe of the large-scale structure at high redshift, z 2. In particular, the Hobby-Eberly Telescope Dark Energy Experiment aims at observing LAEs at 1.9 < z < 3.5 to measure the baryon acoustic oscillation (BAO) scale and the redshift-space distortion (RSD). However, it has been pointed out that the complicated radiative transfer (RT) of the resonant Lyman-α emission line generates an anisotropic selection bias in the LAE clustering on large scales, s 10 Mpc. This effect could potentially induce a systematic error in the BAO and RSD measurements. Also, there exists a recent claim to have observational evidence of the effect in the Lyman-α intensity map, albeit statistically insignificant. Aims. We aim at quantifying the impact of the Lyman-α RT on the large-scale galaxy clustering in detail. For this purpose, we study the correlations between the large-scale environment and the ratio of an apparent Lyman-α luminosity to an intrinsic one, which we call the 'observed fraction', at 2 < z < 6. Methods. We apply our Lyman-α RT code by post-processing the full Illustris simulations. We simply assume that the intrinsic luminosity of the Lyman-α emission is proportional to the star formation rate (SFR) of galaxies in Illustris, yielding a sufficiently large sample of LAEs to measure the anisotropic selection bias. Results. We find little correlation between large-scale environment and the observed fraction induced by the RT, and hence a smaller anisotropic selection bias than has previously been claimed. We argue that the anisotropy was overestimated in previous work due to insufficient spatial resolution; it is important to keep the resolution such that it resolves the high-density region down to the scale of the interstellar medium, that is, ∼ 1 physical kpc. We also find that the correlation can be further enhanced by assumptions in modeling intrinsic Lyman-α emission.
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