Galaxy Parameters¶
Important
A description of the parameter meaning can be found here
-
class
galpak.GalaxyParameters(x=None, y=None, z=None, flux=None, radius=None, inclination=None, pa=None, turnover_radius=None, maximum_velocity=None, velocity_dispersion=None)[source]¶ A simple wrapper for an array of galaxy parameters. It is basically a flat numpy.ndarray of a bunch of floats with convenience attributes for explicit (and autocompleted!) access and mutation of parameters, and nice casting to string.
Warning
Undefined parameters will be NaN, not None.
Example :
from galpak import GalaxyParameters gp = GalaxyParameters(x=1.618) // Classic numpy.ndarray numeric access assert(gp[0] == 1.618) // Autocompleted and documented property access assert(gp.x == 1.618) // Convenience dictionary access, assert(gp['x'] == 1.618) // ... useful when you're iterating : for (name in GalaxyParameters.names): print gp[name]
- Parameters :
- x (pix)
- y (pix)
- z (pix)
- flux
- radius aka. r½ (pix)
- half-light radius in pixel
- inclination (deg)
- pa (deg)
- position angle from y-axis, anti-clockwise.
- turnover_radius aka. rv (pix)
- turnover radius for arctan, exp, velocity profile [is ignored for mass profile]
- maximum_velocity aka. Vmax (km/s)
- de-projected V_max [forced to be positive, with 180deg added to PA]
- velocity_dispersion aka. s0 (km/s)
Note that all the parameters are lowercase, even if they’re sometimes displayed mixed-case.
- Additional attributes :
- stdev : Optional stdev margin (GalaxyParametersError).
- GalPaK3D fills up this attribute.
-
static
from_ndarray(a)[source]¶ Factory to easily create a GalaxyParameters object from an ordered ndarray whose elements are in the order of GalaxyParameters.names.
Use like this :
from galpak import GalaxyParameters gp = GalaxyParameters.from_ndarray(my_ndarray_of_data)
Return type: GalaxyParameters
Description¶
A GalaxyParameters object gp is merely a glorified numpy.ndarray with convenience accessors and mutators :
| Component | Description |
|---|---|
| gp.x | X coordinates of the center of the galaxy. (in pixels) |
| gp.y | Y coordinates of the center of the galaxy. (in pixels) |
| gp.z | Z coordinates of the center of the peak. (in pixels) |
| gp.flux | Sum of the values of all pixels. (in the unit of the cube) |
| gp.radius | Radius of the galaxy. (in pixels) |
| gp.inclination |br| gp.pitch | Inclination of the galaxy (in degrees), aka. pitch along observation axis. |
| gp.pa |br| gp.roll | Position Angle, clockwise from Y (in degrees), aka. roll along observation axis. |
| gp.rv |br| gp.turnover_radius | Inverse factor rv in expression arctan(r/rv). |
| gp.maximum_velocity | Maximum Velocity. (in km/s) |
| gp.velocity_dispersion |br| gp.sigma0 | Disk Dispersion spatially constant (in km/s) added in addition to kinematics dispersion. |
Warning
the velocity_dispersion parameter is NOT the total dispersion. This parameter is akin to a turbulent term. It is added in quadrature to the dispersions due to the disk model and to the thickness. See Cresci et al. 2009, Genzel et al. 2011, and Bouche et al. 2015
You still can access the parameters like an indexed array
assert gp.x == gp[0] # true
assert gp.y == gp[1] # true
# ...
assert gp.sigma0 == gp[9] # true
You may instantiate a GalaxyParameters object like so
from galpak import GalaxyParameters
gp = GalaxyParameters(z=0.65)
gp.x = 5.
assert gp.z == 0.65 # true
assert gp.x == 5. # true
Warning
An undefined value in GalaxyParameters will be nan, not None
assert math.isnan(gp.pa) # true
assert gp.pa is None # false
Getting the Wavelength¶
The z attribute in a GalaxyParameter is in pixels,
you may want the value in the physical unit specified in your Cube’s header.
To that effect, you may use the wavelength_of method of the HyperspectralCube:
from galpak import GalPaK3D
gk = GalPaK3D('my_muse_cube.fits')
gk.run_mcmc()
wavelength = gk.cube.wavelength_of(gk.galaxy.z)
