What Do the Spectral Line Graphs Show?
For each of three locations within M82, the above three spectral line graphs tell us how much CO gas is present, how fast this gas is moving, and whether the motion is towards or away from us. The graph corresponding to the left side of M82 , as viewed in the top radiomap, shows the CO gas is moving away from us at about 300 km/s (kilometers per second). At the opposite (right) side of the galaxy, CO gas is moving away from us at approximately 100 km/s , as indicated in the bottom graph (D). In between these locations (see middle graph), the gas appears to be moving away from us at a velocity of 200 km/s, i.e. roughly half-way between the other velocities. From this scenario, we can infer that the gas in M82 is rotating clockwise around the center of that galaxy, which, as a whole, is moving away from us at 200 km/s. With respect to the center of the galaxy, the gas at A is moving at a net 300 – 200 = 100 km/s, i.e., here the rotation of the gas causes it to move away from us at an add
