The HI disc of the Milky Way Galaxy
Joachim Köppen Kiel Nov 2020
This tool computes from a simple model of the gas distribution
of the disc of the Milky Way the expected profile of the signal strength for
any of the relevant parameters:
- the neutral gas is assumed to have an Outer radius of about 25 kpc
- its density falls off with radius exponentially with a Radial scalelength
of about 8 to 10 kpc. Note that the gas is less strongly concentrated to
the centre than the stars, which have a radial scalelength of about 3 kpc.
- below and above the plane, the gas density falls off like a gaussian
function with a Scaleheight of about 140 pc, which is less than
the stars (up to 300 pc).
- the observer's position in the Milky Way we shall assume as being
at the Sun, which is in the Galactic plane (z=0), at y=8.5 kpc radial distance
on the y-axis (i.e. x=0).
- we may take measurements at one or several directions, specified
by the galactic longitude
- we may choose to look at the true distribution or
as smoothed with antenna HPBW:
- the antenna HPBW (half-power beamwidth) is the angular width of
the principal lobe of our antenna, and represents the angular resolution
our telescope is capable of.
- Hitting the Enter key after changing a value will display the new model.
The left panel is a false colour map of the intensity as a function of
galactic longitude and latitude. The right panel is a plot of the intensity profile
in latitude at the specific longitude. For longitudes away from the Galactic Centre
the red curve is the profile normalized to the maximum at the Galactic Centre,
the blue curve is normalized to its peak value.
The resulting FWHM thickness is displayed at lower left.