Bipolar Blobs as Evidence of Hidden AGN Activities in the Low-mass Galaxies

Abstract

We report evidence of a hidden black hole (BH) in a low-mass galaxy, MaNGA 9885-9102, and provide a new method to identify active BHs in low-mass galaxies. This galaxy is originally selected from the MaNGA survey with distinctive bipolar Hα blobs at the minor axis. The bipolar feature can be associated with active galactic nuclei (AGN) activity, while the two blobs are classified as the H ii regions on the BPT diagram, making the origins confusing. The Swift UV continuum shows that the two blobs do not have UV counterparts, suggesting that the source of ionization is out of the blobs. Consistent with this, the detailed photoionization models prefer AGN rather than the star-forming origin with a significance of 5.8σ. The estimated BH mass is MBH ∼ 7.2 × 105M⊙ from the MBH–σ* relationship. This work introduces a novel method for detecting the light echo of BHs, potentially extending to intermediate mass, in low-metallicity environments where the traditional BPT diagram fails.