Similarly to Fourier space at nonlinear level, however, one has to take into consideration the correlation between the density and velocity fields as well as the contribution from the one-point PDF, as several authors have recently studied (see e.g., Scoccimarro, 2004 Reid & However, the complexity arises because of a convolution with the pairwise velocity PDF which is weighted by density fields at two points and hence scale-dependent.Īt linear level, the mean of the pairwise velocity PDF is related to coherent infall motion and hence the Kaise factor, while its dispersion is related to the velocity power spectrum (Fisher, 1995). Īn advantage of Eq. ( 15) is that the redshift-space correlation function can be expressed only in terms of quantities in real space. Similarly to the selection effects, this canĬause both isotropic and anisotropic distortions in the two-point statistics. Space when the radiative transfer modifies the spectral features from which the Space signal, there can be additional distortions purely arising in redshift While these real space distortions automatically propagate into the redshift Similarly the detection of emitters might be affectedīy their large-scale environment, which can also give rise to anisotropic An isotropic distortionĮffectively corresponds to changing the bias due to emitters of different mass range being favorably detected. ![]() Modifications to the two-point statistics. Others based on their environment, introducing both isotropic and anisotropic In real space thisĬorresponds to a selection effect favoring certain LAEs to be detected over This can introduce new distortion effects in theĬosmological signal both in real space and redshift space. Scatterings of neutral hydrogen change both frequency and position of photonsīefore escaping towards the observer. 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).Īlthough 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. 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. 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. 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.Īdopting the same simulation framework, we further study the impact of RT on the LAE clustering in redshift space. ![]() Guided by RT simulations, prior studies investigated the impact of RT on the large-scale 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. ![]() 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).
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