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

Abstract

We analyze the physical properties of post-starburst AGN SDSS J085338.27+033246.1 according to its optical spectrum and discuss its implications on AGN's evolution. The spectra PCA method is developed to extract emission lines and absorption features from the total light spectrum. The emission-line analysis indicates that the object can be classified as a NLS1 with 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 intermediately strong radio emission. A simple SSP model indicates that the absorption features 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 smaller than the past average SFR$\sim70M_{\odot}\rm{yr^{-1}}$, however. The line ratio diagnosis using the BPT diagrams indicates that the narrow emission lines are almost entirely emitted from HII regions. We further discuss a possible evolutionary path that links AGN and starburst phenomena.