Evolutionary Implications from SDSS J085338.27+033246.1: A Spectacular Narrow‐Line Seyfert 1 Galaxy with Young Poststarburst

We analyze the physical properties of post-starburst AGN SDSSJ085338.27+033246.1 according to its optical spectrum and discuss itsimplications on AGN's evolution. The spectra PCA method is developed to extractemission lines and absorption features from the total light spectrum. Theemission-line analysis indicates that the object can be classified as a NLS1with FeII/H$\beta_{\rm{B}}=2.4\pm0.2$, large Eddington ratio ($\sim0.34$),small black hole mass ($\sim1.1\times10^{7}M_{\odot}$) and intermediatelystrong radio emission. A simple SSP model indicates that the absorptionfeatures are reproduced by a $\sim$100 Myr old starburst with a mass of$\sim7\times10^{9}M_{\odot}$ rather well. The current SFR$\sim3.0M_{\odot}\rm{yr^{-1}}$ inferred from the [OII] emission is much smallerthan the past average SFR$\sim70M_{\odot}\rm{yr^{-1}}$, however. The line ratiodiagnosis using the BPT diagrams indicates that the narrow emission lines arealmost entirely emitted from HII regions. We further discuss a possibleevolutionary path that links AGN and starburst phenomena.Comment: 20 pages, 5 figures, accepted by Ap