On the nature of type 1 AGN: emission properties and correlations

We present a study of emission properties and correlations of 3191 type 1 AGN at 0.02 ≤ z ≤ 0.35, selected from Sloan Digital Sky Survey Data Release 12. We supplement the data with photometric measurements from ROSAT, GALEX, 2MASS, and FIRST, UV spectral properties from HST and IUE, along with X-ray properties from CSC and XMM-Newton SSC. We find the following. (1) Low ionization lines, [O II] λ3727, [N II] λ6548, [S II] λλ6717, 6731 luminosities increase with increasing z while intermediate ionization lines, [O III] λ5007 luminosity does not increase with z consistent with no evolution in AGN SED. We suggest the increasing luminosity of [O II] is caused by host galaxy contribution. The star formation rates that estimated from [O II] luminosities show a flatter increase with z than non-AGN galaxies which indicates lower star formation activity across z in type 1 AGN host galaxies. (2) The luminosities of all measured narrow lines, [O II], [O III], Hβ, Hα, [N II], and [S II], show a Baldwin effect relative to broad Hβ luminosity with slopes in the range of −0.33 to −0.53. We did not find any correlation between Baldwin slopes with ionization potential or critical density of the lines. (3) The observed spectral diversity of type 1 AGN can be unified by Eddington ratio and orientation. Objects with higher Eddington ratio tend to have narrower broad Hβ component, strong Fe II emission, systematic blueshift of C IV λ1549, soft X-ray excess, and lower ionization parameter. In contrast, objects with lower Eddington ratio tend to have broader broad Hβ component, weak Fe II emission, almost absence of systematic blueshift of C IV λ1549 or soft X-ray excess, and higher ionization parameter. Key words: galaxies: active – quasars: emission lines