Very blue-shifted broad H$\alpha$ in a low redshift Type-1.9 AGN: a disk emitter or a recoiling black hole scenario

Abstract

In this manuscript, very blue-shifted broad H$\alpha$ with shifted velocity $\sim$2200km/s is reported in the low redshift Type-1.9 AGN SDSS J1052+1036. Blue-shifted broad emission lines may arise due to the presence of a rotating gas disk around central black hole (BH), but may also be a signature of rare phenomena such as gravitational wave recoil of a supermassive BH (rSMBH) or the presence of a binary BH (BBH) system. Here, due to larger shifted velocity of stronger and wider blue-shifted broad H$\alpha$, the BBH system is disfavoured. Meanwhile, if this object contained a rSMBH, intrinsic obscuration with E(B-V)$\le$0.6 should lead to a detectable broad H$\beta$, indicating the rSMBH scenario not preferred. We find that the blue-shifted broad H$\alpha$ can be well explained by emission from an AGN disk, indicating that SDSS J1052+1036 is likely a disk-emitting AGN. In order to determine which scenario, a rSMBH or a disk emitter, is more preferred, a re-observed spectrum in 2025 can provide robust clues, with a disk emitter probably leading to clear variations of peak positions, peak separations and/or peak intensity ratios in broad H$\alpha$, but with a rSMBH scenario probably leading to no variations of peak separations in broad H$\alpha$.