EVIDENCE FOR THE INTERMEDIATE BROAD-LINE REGION OF REVERBERATION-MAPPED ACTIVE GALACTIC NUCLEUS PG 0052+251

We study the properties of the broad-line region (BLR) of a well-known reverberation-mapped active galactic nucleus (AGN) in order to find reliable evidence for the intermediate BLR. We first check properties of the mapped AGN collected from the literature in the plane of σ2Hβ/σHα2 versus R HαBLR/RBLRHβ. Commonly, virial black hole masses based on observed broad Hα and Hβ should be coincidental. However, among the mapped objects, PG 0052 and NGC 4253 are two apparent outliers in the plane of σ2Hβ/σHα2 versus R HαBLR/RBLRHβ, which indicates that BLRs of PG 0052 and NGC 4253 have some special characters. Based on the 55 public spectra of PG 0052, the BLR of PG 0052 has been carefully studied in detail. We find that the line width ratio of the total observed broad Hα to the total observed broad Hβ is ∼0.7, which is much smaller than the theoretical/observational value of ∼0.9. Furthermore, the flux ratio of the total broad Hα to the total broad Hβ is about 6.8 (Balmer decrement), which is not a reasonable value for the blue quasar PG 0052+251. Moreover, properties of line cores based on the principal component analysis technique confirm that there is one inner broad component and one seriously obscured intermediate broad component in the BLR of PG 0052. If the seriously obscured intermediate BLR was accepted, properties of PG 0052 in the plane of σ2Hβ/σHα2 versus R HαBLR/RBLRHβ could be reproduced, which indicates that the intermediate BLR actually is appropriate for the mapped quasar PG 0052+251. Finally, the large distance between the inner and the intermediate components of the BLR based on the results of the cross-correlation function rejects the possibility that the intermediate component is probably an extended part of the inner component of the BLR.