vice.toolkit.J21_sf_law¶
The default star formation law of the milkyway
object. This is a
callable object, accepting simulation time and either star formation rate
or gas supply as second arguments. By default, it implements the star
formation law adopted in Johnson et al. (2021, in prep) 1.
Signature: vice.toolkit.J21_sf_law(area, **kwargs)
New in version 1.2.0.
Warning
In a milkyway
object, every zone has an instance of this
class as its tau_star
attribute. Any modifications to the attributes
of this class should be made for every zone; if this is not
ensured, the star formation law will not be consistent across all
zones.
Parameters¶
- areareal number
The value of the attribute
area
. See below.- **kwargsvarying types
Other attributes can have their values set via keyword. See below.
Attributes¶
- areareal number
The surface area in \(kpc^2\) of the corresponding annulus in a
milkyway
model.- present_day_molecularreal number [default2.0]
The depletion time of molecular gas at the present day in Gyr. Positive definite.
- molecular_indexreal number [default0.5]
The power-law index on the time-dependence.
- Sigma_g1real number [default5.0e+06]
The smaller of the two surface densities of gas at which there is a break in the Kennicutt-Schmidt relation. Assumes units of \(M_\odot kpc^{-2}\).
- Sigma_g2real number [default2.0e+07]
The larger of the two surface densities of gas at which there is a break in the Kennicutt-Schmidt relation. Assumes units of \(M_\odot kpc^{-2}\).
- index1real number [default1.7]
The index of the power-law at gas surface densities below
Sigma_g1
.- index2real number [default3.6]
The index of the power-law at gas surface densities between
Sigma_g1
andSigma_g2
, above which it is assumed to be linear.- modestr [“sfr”, “ifr”, or “gas”] [default“ifr”]
The mode of the
milkyway
object.
Calling¶
Calling this object will calculate the star formation efficiency timescale
\(\tau_\star\) according to the parameters of the star formation law
entered as attributes of this object. As in the singlezone
object, this
timescale is the gas supply per unit star formation in Gyr.
Parameters:
- timereal number
Simulation time in Gyr. Postive definite.
- arg2real number
Either the gas supply in \(M_\odot\) or the star formation rate in \(M_\odot Gyr^{-1}\). Will be called by VICE directly. With the attribute
area
, the surface density of the corresponding quantity is known. Positive definite.
Returns:
- tau_starreal number
The star formation efficiency timescale given that simulation time and star formation rate/gas supply, in Gyr (as necessary).
See also
vice.milkyway
Notes¶
This object encodes the parameters of the desired Kennicutt-Schmidt relation
into the milkyway
object. This is the relationship relating the surface
densities of star formation \(\dot{\Sigma}_\star\) and gas
\(\Sigma_\text{gas}\).
This object implements a star formation law in the milkyway
object
defined according to:
The value of the power-law index \(N\) has two breaks, at \(\Sigma_{\text{gas},1}\) and \(\Sigma_{\text{gas},2}\).
The values \(\gamma_1\) and \(\gamma_2\) correspond to the
attributes index1
and index2
, respectively. As their names would
suggest, \(\Sigma_{\text{gas},1}\) and \(\Sigma_{\text{gas},2}\)
correspond to Sigma_g1
and Sigma_g2
.
The depletion time of molecular gas due to star formation \(\tau_\text{mol}\) is defined according to the following scaling:
where \(t_0\) is the age of the universe today, \(t\) is the age of
the universe at some simulation time, and \(\tau_{\text{mol},0}\) is
\(\tau_\text{mol}\) at the present day. Because the milkyway
model
only supports lookback times up to 13.2 Gyr, the relation between age of
the universe and simulation time is a simple linear translation:
with the assumption that \(t_0\) = 13.7 Gyr is the age of the universe at the present day.
- 1
Johnson et al. (2021, in prep)