Lyman-
α
(Ly
α
) spectra provide insights into the small-scale structure and kinematics of neutral hydrogen (HI) within galaxies as well as the ionization state of the intergalactic medium (IGM). The ...former defines the intrinsic spectrum of a galaxy, which, in turn, is modified by the latter. These two effects are degenerate. Using the IllustrisTNG100 simulation, we studied the impact of the IGM on Ly
α
spectral shapes between
z
∼ 0 and 5. We computed the distribution of the expected Ly
α
peaks and of the peak asymmetry for different intrinsic spectra, redshifts, and large-scale environments. We find that the averaged transmission curves that are commonly applied give a misleading perception of the observed spectral properties. We show that the distributions of peak counts and asymmetry can lift the degeneracy between the intrinsic spectrum and IGM absorption. For example, we expect a significant number of triple-peaked Ly
α
spectra (up to 30% at
z
∼ 3) if the galaxies’ HI distribution become more porous at higher redshift, as predicted by cosmological simulations. We provide a public catalog of transmission curves for simulations and observations to allow for a more realistic IGM treatment in future studies.
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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 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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Abstract
Major mergers are considered to be a significant source of turbulence in clusters. We performed a numerical simulation of a major merger event using nested-grid initial conditions, adaptive ...mesh refinement, radiative cooling of primordial gas and a homogeneous ultraviolet background. By calculating the microscopic viscosity on the basis of various theoretical assumptions and estimating the Kolmogorov length from the turbulent dissipation rate computed with a subgrid-scale model, we are able to demonstrate that most of the warm–hot intergalactic mediums can sustain a fully turbulent state only if the magnetic suppression of the viscosity is considerable. Accepting this as premise, it turns out that ratios of turbulent and thermal quantities change only little in the course of the merger. This confirms the tight correlations between the mean thermal and non-thermal energy content for large samples of clusters in earlier studies, which can be interpreted as second self-similarity on top of the self-similarity for different halo masses. Another long-standing question is how and to which extent turbulence contributes to the support of the gas against gravity. From a global perspective, the ratio of turbulent and thermal pressures is significant for the clusters in our simulation. On the other hand, a local measure is provided by the compression rate, i.e. the growth rate of the divergence of the flow. Particularly for the intracluster medium, we find that the dominant contribution against gravity comes from thermal pressure, while compressible turbulence effectively counteracts the support. For this reason, it appears to be too simplistic to consider turbulence merely as an effective enhancement of thermal energy.
Major mergers are considered to be a significant source of turbulence in clusters. We performed a numerical simulation of a major merger event using nested-grid initial conditions, adaptive mesh ...refinement, radiative cooling of primordial gas, and a homogeneous ultraviolet background. By calculating the microscopic viscosity on the basis of various theoretical assumptions and estimating the Kolmogorov length from the turbulent dissipation rate computed with a subgrid-scale model, we are able to demonstrate that most of the warm-hot intergalactic medium can sustain a fully turbulent state only if the magnetic suppression of the viscosity is considerable. Accepting this as premise, it turns out that ratios of turbulent and thermal quantities change only little in the course of the merger. This confirms the tight correlations between the mean thermal and non-thermal energy content for large samples of clusters in earlier studies, which can be interpreted as second self-similarity on top of the self-similarity for different halo masses. Another long-standing question is how and to which extent turbulence contributes to the support of the gas against gravity. From a global perspective, the ratio of turbulent and thermal pressures is significant for the clusters in our simulation. On the other hand, a local measure is provided by the compression rate, i.e. the growth rate of the divergence of the flow. Particularly for the intracluster medium, we find that the dominant contribution against gravity comes from thermal pressure, while compressible turbulence effectively counteracts the support. For this reason it appears to be too simplistic to consider turbulence merely as an effective enhancement of thermal energy.
A&A 614, A31 (2018) Lyman-$\alpha$ emitters (LAEs) are a promising probe of the large-scale
structure at high redshift, $z\gtrsim 2$. 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, Zheng et al. (2011) pointed out that the complicated
radiative transfer (RT) of the resonant Lyman-$\alpha$ emission line generates
an anisotropic selection bias in the LAE clustering on large scales, $s\gtrsim
10$ Mpc. This effect could potentially induce a systematic error in the BAO and
RSD measurements. Also, Croft et al. (2016) claims an observational evidence of
the effect in the Lyman-$\alpha$ intensity map, albeit statistically
insignificant. We aim at quantifying the impact of the Lyman-$\alpha$ 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-$\alpha$ luminosity to an intrinsic one, which we call the `observed
fraction', at $2<z<6$. We apply our Lyman-$\alpha$ RT code by post-processing
the full Illustris simulations. We simply assume that the intrinsic luminosity
of the Lyman-$\alpha$ emission is proportional to the star formation rate of
galaxies in Illustris, yielding a sufficiently large sample of LAEs to measure
the anisotropic selection bias. We find little correlations between large-scale
environment and the observed fraction induced by the RT, and hence a smaller
anisotropic selection bias than what was claimed by Zheng et al. (2011). We
argue that the anisotropy was overestimated in the previous work due to the
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, $\sim1$ physical kpc. (abridged)
Lyman-\(\alpha\) emitters (LAEs) are a promising probe of the large-scale structure at high redshift, \(z\gtrsim 2\). 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, Zheng et al. (2011) pointed out that the complicated radiative transfer (RT) of the resonant Lyman-\(\alpha\) emission line generates an anisotropic selection bias in the LAE clustering on large scales, \(s\gtrsim 10\) Mpc. This effect could potentially induce a systematic error in the BAO and RSD measurements. Also, Croft et al. (2016) claims an observational evidence of the effect in the Lyman-\(\alpha\) intensity map, albeit statistically insignificant. We aim at quantifying the impact of the Lyman-\(\alpha\) 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-\(\alpha\) luminosity to an intrinsic one, which we call the `observed fraction', at \(2<z<6\). We apply our Lyman-\(\alpha\) RT code by post-processing the full Illustris simulations. We simply assume that the intrinsic luminosity of the Lyman-\(\alpha\) emission is proportional to the star formation rate of galaxies in Illustris, yielding a sufficiently large sample of LAEs to measure the anisotropic selection bias. We find little correlations between large-scale environment and the observed fraction induced by the RT, and hence a smaller anisotropic selection bias than what was claimed by Zheng et al. (2011). We argue that the anisotropy was overestimated in the previous work due to the 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, \(\sim1\) physical kpc. (abridged)
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