Gemini Near-infrared Spectroscopy of High-Redshift Fermi Blazars: Jetted Black Holes in the Early Universe Were Overly Massive

TL;DR

This study uses near-infrared spectroscopy to accurately measure black hole masses in high-redshift Fermi blazars, confirming they host overly massive SMBHs that challenge existing early universe growth models.

Contribution

It provides the first robust virial black hole mass estimates for high-redshift Fermi blazars using near-IR spectroscopy, improving upon previous biased optical-based methods.

Findings

High-redshift Fermi blazars host overly massive SMBHs.

New virial BH mass estimates are consistent with previous suggestions.

Results challenge models of rapid early SMBH growth.

Abstract

Jetted active galactic nuclei (AGNs) are the principal extragalactic $\gamma$-ray sources. Fermi-detected high-redshift ($z>3$) blazars are jetted AGNs thought to be powered by massive, rapidly spinning supermassive black holes (SMBHs) in the early universe ($<2$ Gyr). They provide a laboratory to study early black hole (BH) growth and super-Eddington accretion -- possibly responsible for the more rapid formation of jetted BHs. However, previous virial BH masses of $z>3$ blazars were based on C IV in the observed optical, but C IV is known to be biased by strong outflows. We present new Gemini/GNIRS near-IR spectroscopy for a sample of nine $z>3$ Fermi $\gamma$-ray blazars with available multi-wavelength observations that maximally sample the spectral energy distributions (SEDs). We estimate virial BH masses based on the better calibrated broad H$\beta$ and/or Mg II . We compare the new virial BH masses against independent mass estimates from SED modeling. Our work represents the first step in campaigning for more robust virial BH masses and Eddington ratios for high-redshift Fermi blazars. Our new results confirm that high-redshift Fermi blazars indeed host overly massive SMBHs as suggested by previous work, which may pose a theoretical challenge for models of the rapid early growth of jetted SMBHs.