F6 - spectrum of a galaxy

ellipticals

• they are dominated by old stellar populations with negligible gas in the ISM
• G/K stars peak towards red optical with absorption lines from hydrogen and metals
• there is little to no emission

spirals

• they are dominated by young steallar populations with ISM gas
• the composite spectrum is similar to O/B/A stars along with emmision lines from HII
• the peak is in bluer
• old stellar populations contribute, but are outshone by younger, more luminous stars