A protogalaxy is a gas cloud forming a galaxy. They are presumed to have existed and to be potentially observable at high redshifts. Given the theorized history of the universe, they are expected to be frequent over a certain range of redshifts. Their expected spectrum would be similar to a starburst galaxy, with hydrogen, helium, insignificant metallicity, and with electromagnetic radiation from the energy release of gravitational binding energy.
Some candidates have been observed, but they are not yet convincingly identified.