Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. IX 10 New Observations of Reverberation Mapping and Shortened H$\beta$ Lags

TL;DR

This study presents new reverberation mapping observations of supermassive black holes with high accretion rates, revealing shorter Hβ lags than predicted and highlighting the influence of accretion rate and black hole spin on emission line relations.

Contribution

It provides new measurements of Hβ lags in 10 SEAMBHs, demonstrating the dependence of lag shortening on accretion rate and proposing revisions to the canonical R_Hβ-L_5100 relation for high accretion rate AGNs.

Findings

Hβ lags are shorter than predicted by standard relations in high accretion rate AGNs.

Fe II strength and Hβ profile serve as proxies for accretion rate.

Shortened Hβ lags support the presence of retrograde accretion onto black holes.

Abstract

As one of the series of papers reporting on a large reverberation mapping campaign of super-Eddington accreting massive black holes (SEAMBHs) in active galactic nuclei (AGNs), we present the results of 10 SEAMBHs monitored spectroscopically during 2015-2017. Six of them are observed for the first time, and have generally higher 5100 \AA\ luminosities than the SEAMBHs monitored in our campaign from 2012 to 2015; the remaining four are repeat observations to check if their previous lags change. Similar to the previous SEAMBHs, the H$\beta$ time lags of the newly observed objects are shorter than the values predicted by the canonical $R_{\mathrm{H\beta}}$-$L_{5100}$ relation of sub-Eddington AGNs, by factors of $\sim2-6$, depending on the accretion rate. The four previously observed objects have lags consistent with previous measurements. We provide linear regressions for the $R_{\mathrm{H\beta}}$-$L_{5100}$ relation, solely for the SEAMBH sample and for low-accretion AGNs. We find that the relative strength of Fe II and the profile of the H$\beta$ emission line can be used as proxies of accretion rate, showing that the shortening of H$\beta$ lags depends on accretion rates. The recent SDSS-RM discovery of shortened H$\beta$ lags in AGNs with low accretion rates provides compelling evidence for retrograde accretion onto the black hole. These evidences show that the canonical $R_{\mathrm{H\beta}}$-$L_{5100}$ relation holds only in AGNs with moderate accretion rates. At low accretion rates, it should be revised to include the effects of black hole spin, whereas the accretion rate itself becomes a key factor in the regime of high accretion rates.