Cosmological Radiative Transfer Simulations of Lyman-alpha Emission

class: center, middle

.title[Cosmological Radiative Transfer Simulations of Lyman-alpha Emission]

.author[Chris Byrohl]

.coauthor[*Collaborators*: Christoph Behrens, Shun Saito, Jens Niemeyer]

.institution[
<img style="margin: 0px auto;display:block;width:20%;" src="../figures/MPA-Logo.png"></img>
Max Planck Institute for Astrophysics, Garching]

.date[Aspen, February 05, 2018]

---
# Motivation

* Ly-`$\alpha$`: Prominent emission line for high-`$z$` galaxies

## <span style="color:MediumSeaGreen">Opportunity</span>:

* Low redshifts (2<z<3.5): Cosmology with HETDEX
* High redshift: Complementary reionization probe

## <span style="color:IndianRed">Theoretical Challenge</span>:

* Resonant line and high optical depths

<p style="padding-left:1.5em">→Complex radiative transfer →numerical simulations</p>

.blockquote[Selection Effect Analysis: 
<a href="https://arxiv.org/abs/1710.06171.pdf">arXiv:1710.06171</a> (C. Behrens,
<b>CB</b> et al.)]

---
# Reminder: Redshift Space Distortions

.left-column[
$${\color{red}\vec{s}}={\color{blue}\vec{r}}+\frac{\vec{v}\cdot\hat{z}}{a H(z)}{\color{green}\hat{z}}$$
]
.right-column-definitions[
$$ \begin{align} {\color{red}\vec{s}}&:\text{redshift  space} \\\\ 
{\color{blue}{\vec{r}}}&: \text{real space} \\\\
{\color{green}{\hat{z}}}&: \text{line of sight direction} \end{align} $$
]

<font color=SteelBlue>Fingers-of-God effect</font>: 
<b>Elongation</b> due to random motion on small scales

<font color=ForestGreen>Kaiser effect</font>:
<b>Squashing</b> due to coherent motion on large scales

---
# RT Clustering

## Theory 
 <p style="text-align: justify;">
 → (<a href="https://arxiv.org/pdf/1003.4990v3.pdf">Zheng et al., 2011</a>)
	 find anisotropic clustering due to a <b>Radiative Transfer Effect.</b>
</p>

<div style="clear:both;"></div>
 <figure style="width:32%;float: left;display:block;"><img style="width:100%;" src="../figures/croft_anisotropy.png"></img>
</figure> 
## Observation

<p style="text-align: justify;">
→ (<a href="https://arxiv.org/abs/1504.04088">Croft et al., 2016</a>)
observe clustering consistent with (<a href="https://arxiv.org/pdf/1003.4990v3.pdf">Zheng et al., 2011</a>).
</p>

<p style="text-align: justify;">
 → Problem for HETDEX? </p>

---
# RT Clustering
<figure style="width:45%;float: right;display:block;"><img style="width:115%;" src="../figures/rteffect_presentation.png">
</figure>

<p style="text-align: justify;hyphens: auto;" lang="en">
Radiative Transfer introduces selection effects:
<ul>
<li style="color:SteelBlue">density (isotropic)</li>
<li style="color:ForestGreen">velocity gradient (anisotropic)</li>
</ul>
</p>
<div style="clear:both;"></div>

<figure style="width:30%;float: left;display:block;"><img style="width:100%;" src="../figures/ZZ_anisotropy_explained.png">
	<figcaption>(<a href="https://arxiv.org/pdf/1003.4990v3.pdf">Zheng et al., 2011</a>)</figcaption>
</figure>

<ul style="list-style:none">
<li style="color:SteelBlue; padding-left:4em;">⬊ Bias</li>
<li style="color:ForestGreen">⬊Clustering along the line of sight</li>
</ul>

---
# Methodology

.left-column[
<figure style="width:65%;float: left;display:block;">
    <img style="width:100%;margin:0px auto;display:block"  src="../figures_aspen/illustris_box_dmdens_gasvel.png">
    <figcaption>Illustris Project.</figcaption>
</figure>

# +
]
.right-column[
<figure style="width:90%;float: right;display:block;">
    <img style="width:100%;margin:0px auto;display:block"  src="../figures/physRT_peelingOff_new.png">
    <figcaption>Radiative Transfer.</figcaption>
</figure>
]

<div style="clear:both;width:100%"></div>
<table style="font-size:130%">
  <tr>
    <th></th>
    <th style="padding:0 2em 0 15px;">Zheng et al. 2011<br></th>
    <th style="padding:0 2em 0 15px;">Behrens et al. 2017<br></th>
  </tr>
  <tr>
    <td style="font-weight: bold;">Resolution<br></td>
    <td style="padding:0.5em 2em 0.5em 15px;">30.4 pkpc</td>
    <td style="padding:0.5em 2em 0.5em 15px;">0.5 pkpc</td>
  </tr>
  <tr>
    <td style="font-weight: bold;">Redshifts<br></td>
    <td style="padding:0 2em 0.5em 15px;">z=5.7 only</td>
    <td style="padding:0 2em 0.5em 15px;">z=2.01,3.01,4.01,5.85</td>
  </tr>
</table>

---
# Results: Some Impressions

---
# Results: Clustering

* Can reproduce RT effect for artificially lowered resolution.
* **IGM** interaction crucially depends on **CGM** processes.

---
# Conclusions/Future Prospects

.finalslide[
- High resolution **numerical simulations** necessary to understand 
**Ly`$\alpha$` complex radiative transfer**.

- Prior publication **overestimated Selection Effects**.

- **Tool for further studies**, 
 - e.g. Redshift space, Intensity mapping.
]