What are Quasar Absorption Lines?
The QSO Spectrum and Its Redshift The remainder of the above schematic is the spectrum of the QSO. The wavelength scale (in angstroms) is provided across the bottom in blue and the spectrum itself is red. Note the narrow peak at 4862 angstroms that is labeled “Ly alpha (z=3)”. This is due to excited neutral hydrogen surounding the QSO itself. Hydrogen absorbs and emits light with wavelength 1215.67 angstroms. This “emission” feature is observed at 1215.67*(1+z) = 4862.68 angstroms, where z=3 is QSO redshift. There is also a little absorption feature at 4770 angstroms due to cooler hydrogen also very near the QSO (shown as red material in the QSO schematic). Note also that there is another clear emission feature labeled “C IV (z=3)” observed at 6195 angstroms. This is due to ionized carbon around the QSO. Not that it also shows some absorption at 6100 angstroms. These Ly-alpha and C IV features are intrinsic to the QSO and help to both identify the object as a QSO and to provide its red
