vice.singlezone.tau_star

Type : real number or <function>

Default : 2.0

The star formation rate per unit gas supply in Gyr, defined by

\[\tau_\star \equiv M_\text{g}/\dot{M}_\star\]

where \(M_\text{g}\) is the ISM gas mass and \(\dot{M}_\star\) is the star formation rate. Numbers will be interpreted as a constant value. Functions must accept either one or two parameters, the first of which will always be time in Gyr. In infall and gas modes, the second parameter will always be interpreted as the gas mass in \(M_\odot\), but in star formation mode, it will be interpreted as the star formation rate in \(M_\odot/yr\). This approach allows this attribute to vary with either the gas mass or the star formation rate in simulation (depending on which mode the model is ran in).

New in version 1.2.0: Prior to version 1.2.0, a functional form for this attribute had to accept only one numerical parameter, always interpreted as time in Gyr.

Tip

In infall and gas modes, this parameter can be set to infinity to forcibly shut off star formation.

Tip

When adopting a functional form for this attribute which depends on the gas supply itself via a pure power-law, we recommend users make use of the attributes schmidt, schmidt_index, and MgSchmidt. These control the parameters of the power-law and allow VICE to calculate the values internally, resulting in shorter integration times.

Note

When the attribute schmidt == True, this is interpreted as the prefactor on gas-dependent star formation efficiency:

\[\tau_\star^{-1} = \tau_{*,\text{specified}}^{-1} \left( \frac{M_\text{g}}{M_\text{g,Schmidt}} \right)^{\alpha}\]

where \(\alpha\) is the power-law index on gas-dependent star formation efficiency, set by the attribute schmidt_index, and \(\tau_{*,\text{specified}}\) is the value of this attribute.

Note

Saving functional attributes with VICE outputs requires the package dill, an extension to pickle in the Python standard library. It is recommended that VICE user’s install dill >= 0.2.0.

Note

In the interstellar medium and star formation literature, this parameter is often referred to as the depletion timescale. In this documentation and in much of the galactic chemical evolution literature, it is often referred to as the “star formation efficiency timescale.”

Note

If the user assigns this attribute a function which is ran through a Cython compiler, the corresponding Cython source code must be compiled with the binding = True directive. This allows VICE to inspect the signature of the compiled function; otherwise, assigning the function to this attribute will raise a ValueError.

Example Code

>>> import vice
>>> sz = vice.singlezone(name = "example")
>>> sz.tau_star = 1
>>> def f(t):
        if 5 <= t <= 6:
                return 1
        else:
                return 2
>>> sz.tau_star = f