Fit rotation model¶
Here is a little introduction to the process of fitting a rotation model to a velocity field. IFSCube has a program for that called fit_rotation, which takes a velocity field from a FITS file and attempts to fit the disk rotation model described in Bertola 1991.
In the examples directory there is a configuration file for fit_rotation. After installation the program should be available at your path, so that you can call it by entering the following in a terminal, from within the examples directory.
fit_rotation rotation.ini
This command assumes that you have already run the cube fitting example with the data for NGC3081.
Configuration file¶
The parameters in the configuration file are directly translated in to arguments
for the methods of the ifscube.rotation.Rotation class.
general¶
- fit: bool
- If yes fits the data, if no just builds a model with the parameters given in the section model.
loading¶
- input_data: str
- Name of the input FITS file containing the velocity field data.
- extension: str or int
- Name or number of the extension in case of a multi-extension FITS file.
- plane: int
- Plane of the velocity field, in case of data cube.
model¶
The model parameters are equal to those of Bertola et al. 1991, except for x_0 and y_0. All angles should be given in degrees.
- amplitude: float
- Amplitude of the velocity field.
- x_0: float
- Horizontal coordinate of the rotation center.
- y_0: float
- Vertical coordinate of the rotation center.
- phi_0: float
- Angle of the line of nodes.
- c_0: float
- Concentration index.
- p: float
- p parameter.
- theta: float
- Inclination angle of the disk with respect to the plane of the sky.
bounds¶
For each parameter of the last section a pair of bounds can be set in this section, repeating the parameter name and given lower and upper bounds separated by a comma.
[bounds]
theta = 30, 60
fixed¶
Parameters can also be set to be fixed, by writing the parameter name in this section followed by a ‘yes’.
[fixed]
x_0 = 'yes'
y_0 = 'yes'