It is also most intense at low frequencies. Hence, we find that the emitted matter moves outward, cools down, expands and emits radio radiation. This radiation is black body radiation and indicates the temperature of the surrounding inter-stellar gas. Using Hubble's law, their distances are measured out to be 100s to 1000s of Mpc away. Since, we can measure their apparent brightness and we know how far they are, we can estimate their intrinsic luminosity and they turn out to be 1000 times brighter than any object ever known.
Some quasars show emission jets and extended emission features.
A lower red-shift indicates that the object is between us and the quasar and the absorption lines give us information about the object's chemical composition, temperature, etc. This is how the spectra of some quasars can be used to probe the space between us and them.