H II/H I Comparisons: A Preview

The above pictures show a small (about 10 degree by 10 degree) region of the sky that has been mapped in the 21-cm emission (left) and H-Alpha line (right). These two lines trace neutral and ionized hydrogen, respectively. Since ionized hydrogen eventually recombines to form neutral hydrogen, the presence of ionized hydrogen requires an active source of ionization. Along with mapping out where the ionized hydrogen is in the galaxy, we also hope to help figure out what keeps it ionized.

The WHAM spectrometer will produce a maps like these of the ionized hydrogen everywhere in the Galaxy visible from the northern hemisphere. The 50-100 fold increase in sensitivity of WHAM over the technique used to produce the small map above has allowed us to survey the whole sky in a little over a year!