Where Tsky is noise generated  by all things above antenna, such as atmospheric temp, temp of background sources that you don't want to detect. Trx is the thermal noise of electrical components in the receiver. 
erg is unit of energy and work = \(10^{-7}\) J
 1 Jansky (Jy), unit of spectral flux density = \(10^{-26}\ \frac{W}{m^2\cdot Hz}\) 
Gain describes how well an antenna converts input power into radio waves headed in a specific direction. 
\(\int_a^bFdV\) =~ HI Mass
v=~ distance 
Width=~ Mass
4500-5500 km/s ~ velocity range for PPS, this is where we are finding most of our detections which makes sense. (Xiao et. al, 2014)