Catastrophysics

Longitude-velocity and Latitude-velocity plots Observing velocity profiles of the HI lines at different longitudes, we can derive a diagram in which the intensity distribution is mapped in the position-velocity space, namely in the l-vr plane. This is called a longitude-velocity diagram. The LV diagram is used for studying the rotation characteristics of the galactic disk as well as to derive the spiral structure.[ Y.Sofue, Galactic Radio Astronomy ]. The HI spectrums that I observed give us the information needed to construct the l-v diagrams. Data I'll write more about the "observation" part in a later post. But for now, just take it that we get the velocities and the corresponding latitudes from this data. Longitude-velocity plots l-v plot at latitude b=0 l-v plot using data at b=0 latitude In the longitude-velocity plot above you can see that the gas isn't spread everywhere i.e not randomly scattered across the velocity space but instead it forms these "str...

Using a radio telescope we can detect the H 21 cm line which is produced by the spin-flip transition in atomic hydrogen. As this line is not attenuated by interstellar dust or by the earth's atmosphere, we can detect it using ground-based telescopes.   The probability of the spin-flip transition is low (lifetime of an excited state t~ 3.5 x 10^14 seconds), meaning that a single hydrogen atom might undergo this transition only once in 11 million years!  But if we point our radio telescope at the sky we do see this transition. Why? Well, because of the vast abundance of hydrogen in the galaxy. If a chance of transition is 10^(-14) but you got around 10^57 hydrogen atoms, then a simple multiplication might give you an idea of how many HI atoms are emitting this transition. This makes it possible to detect the 1.4 GHz line and use it for astronomy. Scanning the galaxy in steps of 5 degrees of galactic latitude you can see the structure of the galaxy pretty easily. Here I have co...