Calculates theta, x and y (image coordinates) for a GALFIT tanh log spiral, as defined in Galfit User’s Manual (Peng 2010), including tilt. :param r_in: Spiral inner radius, in pixels. If this goes extremely negative in fitting, fix to 0.

Corresponds to item R1) in the GALFIT feedme definition.

Parameters¶

r_out: Quantity¶

Spiral outer radius, in pixels. Corresponds to item R2) in the GALFIT feedme definition.

r_ws: Quantity¶

winding scale radius, in pixels. Corresponds to item R4) in the GALFIT feedme definition.

theta_inc: Quantity¶

inclination to line-of-sight, in degrees. Corresponds to item R9) in the GALFIT feedme definition.

theta_pa: Quantity¶

Position angle of the axis about which the galaxy is rotated for inclination. Corresponds to item R10) in the GALFIT feedme definition.

theta_out: Quantity¶

Cumulative rotation to outer radius, in degrees. Corresponds to item R3) in the GALFIT feedme definition.

position_angle: Quantity¶

position angle (PA) of model, in degrees, with up=0 and left=90 Corresponds to item 10) in the GALFIT feedme definition.

x: Quantity¶

x-position of model centre, in pixels. Corresponds to first component of item 1) in the GALFIT feedme definition.

y: Quantity¶

y-position of model centre, in pixels. Corresponds to second component of item 1) in the GALFIT feedme definition.

r: Quantity¶

r coordinate; distance from the centre of the spiral model, in pixels.

tilt: bool = True¶

If True, the spiral is transformed to account for its inclination angle. If False, the output spiral is equivalent to theta_inc == 0 deg.

Returns¶

theta_1, x_1, y_1, theta_2, x_2, y_2, where 1 and 2 refer to each spiral arm.