Complex Ly α Profiles in Redshift 6.6 Ultraluminous Ly α Emitters
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ABSTRACT Existing ubiquitously in the Universe with the highest luminosity, the Lyman-α (Lyα) emission line encodes abundant physical information about the gaseous medium it interacts with. Nevertheless, the resonant nature of the Lyα line complicates the radiative transfer (RT) modelling of the line profile. We revisit the problem of deciphering the Lyα emission line with RT modelling. We reveal intrinsic parameter degeneracies in the widely used shell model in the optically thick regime for both static and outflowing cases, which suggest the limitations of the model. We also explore the connection between the more physically realistic multiphase, clumpy model, and the shell model. We find that the parameters of a ‘very clumpy’ slab model and the shell model have the following correspondences: (1) the total column density, the effective temperature, and the average radial clump outflow velocity of the clumpy slab model are equal to the H i column density, effective temperature, and expansion velocity of the shell model, respectively; (2) large intrinsic linewidths are required in the shell model to reproduce the wings of the clumpy slab models; (3) adding another phase of hot interclump medium increases peak separation, and the fitted shell expansion velocity lies between the outflow velocities of two phases of gas. Our results provide a viable solution to the major discrepancies associated with Lyα fitting reported in previous literature, and emphasize the importance of utilizing information from additional observations to break the intrinsic degeneracies and interpreting the model parameters in a more physically realistic context.more » « less
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ABSTRACT The discovery of giant quasar Ly α nebulae at z > 2 has opened up the possibility to directly study in emission the Circumgalactic and Intergalactic Medium (CGM/IGM). However, the resonant nature of the Ly α line and its different emission mechanisms hamper the ability to constrain both the kinematics and physical properties of the CGM/IGM. Here, we present results of a pilot project aiming at the detection of CGM H α emission, a line which does not suffer from these limitations. To this end, we first used KCWI to detect Ly α emission around three bright quasars with 2.25 < z < 2.27, a range which is free from bright IR sky lines for H α, and then selected the most extended nebula for H α follow-up with MOSFIRE. Within the MOSFIRE slit, we detected H α emission extending up to 20 physical kpc with a total H α flux of FH α = (9.5 ± 0.9) × 10$^{-18}~\mathrm{erg\, s^{-1}\, cm^{-2}}$. Considering the Ly α flux in the same region, we found FLy α/FH α = 3.7 ± 0.3 consistent with that obtained for the Slug Nebula at z = 2.275 and with recombination radiation. This implies high densities or a very broad density distribution within the CGM of high-redshift quasars. Moreover, the H α line profile suggests the presence of multiple emitting components overlapping along our line of sight and relatively quiescent kinematics, which seems incompatible with either quasar outflows capable of escaping the potential well of the host halo or disc-like rotation in a massive halo (>1012 M⊙).more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-4357/aac021
