vice.toolkit.J21_sf_law.molecular
=================================

Calculate the star formation efficiency timescale of molecular gas at
a given simulation time.

**Signature**: x.molecular(time)

Parameters
----------
x : ``J21_sf_law``
	An instance of this class.
time : ``float``
	The simulation time in Gyr.

Returns
-------
tau_star_mol : float
	The star formation efficiency timescale :math:`\tau_\star` for
	molecular gas only (:math:`\tau_\text{mol}`), defined accordingly:

	.. math:: \tau_\text{mol} = \tau_{\text{mol},0}
		\left(\frac{0.5 + t}{t_0}\right)^\gamma

	where :math:`\tau_{\text{mol},0}` is the value of
	:math:`\tau_\text{mol}` at the present day, :math:`t_0` is the
	present-day age of the universe (assumed to be 13.7 Gyr),
	:math:`\gamma` is the power-law index, and :math:`t` is the
	parameter ``time`` passed to this function. A value of 0.5 is added,
	beacuse the onset of star formation is assumed to occur 0.5 Gyr
	following the big bang in the Johnson et al. (2021) models [1]_.

	The values of :math:`\tau_{\text{mol},0}` and :math:`\gamma` are
	controlled by the attributes ``present_day_molecular`` and
	``molecular_index``, respectively.

Example Code
------------
>>> import vice
>>> mw = vice.milkyway(name = "example")
>>> mw.zones[0].tau_star.molecular(0)
0.6617825960083583
>>> mw.zones[0].tau_star.molecular(5)
1.3776103291490314
>>> mw.zones[0].tau_star.molecular(13.2)
2.0

.. [1] Johnson et al. (2021), MNRAS, 508, 4484