Evidence for Intermediate BLR of Reverberation-Mapped AGN PG 0052+251

Abstract

In this manuscript, we study properties of BLR of well-known reverberation-mapped AGN, in order to find reliable evidence for intermediate BLR. We firstly check properties of mapped AGN collected from literature in plane of $\sHb^2/\sHa^2$ vs $\RHa/\RHb$. Commonly, virial BH masses based on observed broad H$\alpha$ and H$\beta$ should be coincident. However, among the mapped objects, PG0052 and NGC4253 are two apparent outliers in the plane of $\sHb^2/\sHa^2$ vs $\RHa/\RHb$, which indicate BLRs of PG0052 and NGC4253 have some special characters. Then based on the 55 public spectra of PG0052, BLR of PG0052 is been carefully studied in detail. We find that line width ratio of total observed broad H$\alpha$ to total observed broad H$\beta$ is $\sim$0.7, which is much smaller than theoretical/observational value of $\sim$0.9. Furthermore, flux ratio of total broad H$\alpha$ to total broad H$\beta$ is about 6.8 (Balmer Decrement), which is not one reasonable value for BLUE quasar PG 0052+251. Moreover, properties of line cores based on PCA technique confirm there is one inner broad component and one seriously obscured intermediate broad component in BLR of PG0052. If the seriously obscured intermediate BLR was accepted, properties of PG0052 in the plane of $\sHb^2/\sHa^2$ vs $\RHa/\RHb$ could be well reproduced, which indicates that the intermediate BLR actually is well appropriate to mapped quasar PG 0052+251. Finally, the large distance between inner component of BLR and intermediate component of BLR based on CCF results rejects the possibility that the intermediate component is probably extended part of inner component of BLR.