Narrow-Line Regions and the Different Classes of Quasar

Astronomy and Astrophysics – Astronomy

Scientific paper

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Quasars, Radio-Emission, Fe Ii Emission, Narrow-Line Seyfert 1, Nls1, Eigenvector 1

Scientific paper

The equivalent width of the [O III] 5007 line and the relative intensity of the Fe II 4570 blend have been studied in a large sample of quasars of all three main radio classes (steep spectrum, flat spectrum, and radio quiet). Confirming earlier work, it is found that most of the flat radio spectrum quasars have strong optical Fe II emission (Fe II 4570/Hbeta > 0.5), but that none of the steep radio spectrum quasars have it. 20% of the radio-quiet quasars have strong optical Fe II. In addition to these differences, the radio-quiet QSOs and the steep radio spectrum QSOs have significantly greater [O III] 5007 equivalent widths than the flat radio spectrum ones. The difference is most pronounced if one divides up the QSOs on the basis of optical Fe II emission. The strong optical Fe II emitters have a median [O III] 5007 equivalent width three times greater than the weak optical Fe II emitting quasars. These differences show that the broad-line region, the narrow-line region, and the radio emission are related. These differences present severe difficulties for models of quasar activity that seek to unify the different kinds of quasar using orientation effects. Instead, the differences favor galactic environment as the factor governing what type of quasar is seen. No luminosity dependence is seen in the equivalent width of [O III[ 5007 within each radio class.

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