Unobscured Central Broad-line Regions in Type-1.9 AGN SDSS J1241+2602

Abstract

Strong evidence is reported to support unobscured broad-line regions (BLRs) in Type-1.9 active galactic nucleus (AGN) SDSS J1241+2602 with reliable broad H α but no broad H β . Commonly, the disappearance of broad H β can be explained by the AGN unified model, in which heavily obscured BLRs are expected in Type-1.9 AGNs. Here, based on properties of two kinds of BH masses, the virial BH mass and the BH mass obtained through the M _BH – σ relation, an independent method is proposed to test whether there are unobscured central BLRs in a Type-1.9 AGN. By the reliable measurement of stellar velocity dispersion of about 110 ± 12 km s ^−1 through the host galaxy absorption features in SDSS J1241+2602, the BH mass obtained through the M _BH – σ relation is consistent with the virial BH mass (3.43 ± 1.25) × 10 ^7 M _⊙ determined through properties of the observed broad H α without considering the effects of obscurations in SDSS J1241+2602. Meanwhile, if considering heavily obscured BLRs in SDSS J1241+2602, the reddening-corrected virial BH mass is tens of times larger than the value expected from M _BH – σ , leading SDSS J1241+2602 to be an outlier in the M _BH – σ space with a confidence level higher than 5 σ . Therefore, unobscured BLRs are preferred in the Type-1.9 AGN SDSS J1241+2602. The results indicate that it is necessary to check whether unobscured central BLRs are common in Type-1.9 AGNs when testing the unified model of AGNs through properties of Type-1.9 AGNs.

Keywords

• Active galactic nuclei
• Active galaxies
• Emission line galaxies
• Supermassive black holes