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

xJ21_sf_law

An instance of this class.

timefloat

The simulation time in Gyr.

Returns

tau_star_molfloat

The star formation efficiency timescale \(\tau_\star\) for molecular gas only (\(\tau_\text{mol}\)), defined accordingly:

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

where \(\tau_{\text{mol},0}\) is the value of \(\tau_\text{mol}\) at the present day, \(t_0\) is the present-day age of the universe (assumed to be 13.7 Gyr), \(\gamma\) is the power-law index, and \(t\) 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 \(\tau_{\text{mol},0}\) and \(\gamma\) 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