.. _HeII_to_HI_column_density_ratio:

HeII-to-HI column density ratio
===============================

**Field names**: 
"HeII_to_HI_column_density_ratio", "eta"

**Units**: 


**Remarks**: 


**Required fields**: 
"redshift"


    
Data
^^^^

.. note::
    Hover on data points to visualize their coordinates and the source. Click on a legend entry to hide it, double
    click on a legend entry to hide everything else. 

    Circles indicate measurements. Upper-/lower-pointing triangles indicate upper/lower limits.

.. raw:: html
    :file: ../plots/plots/HeII_to_HI_column_density_ratio.html


`[open plot in separate tab]`_
------------------------------

.. _[open plot in separate tab]: ../plots/HeII_to_HI_column_density_ratio.html

Data sources
^^^^^^^^^^^^

.. note::
    
    Cannot find your favorite constraint? Consider :ref:`AddYourConstraint`!

* |Syphers & Shull 2014|

.. |Syphers & Shull 2014| raw:: html

   <a href="https://iopscience.iop.org/article/10.1088/0004-637X/784/1/42" target="_blank">Syphers & Shull 2014</a>