The quasar main sequence of highly accreting NLSy1 galaxies

Abstract

The quasar main sequence, or Eigenvector 1 (EV1), describes the optical diversity of active galactic nuclei, with Narrow-Line Seyfert 1 (NLSy1) galaxies anchoring the high-accretion end. Recent discoveries of overly massive black holes in the early Universe highlight the need to study low-redshift low-mass super-Eddington accretors as analogs for rapid black hole seed growth. We mapped a newly discovered large population of 18,749 NLSy1 galaxies identified in the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1) onto the EV1 plane and compared them with the SDSS-DR17 NLSy1 population analyzed in a homogeneous way. We compared the spectral properties of the DESI-DR1 NLSy1 sample with the SDSS-DR17 NLSy1 catalog. We extracted the key parameters, including the broad Hβ full width at half maximum and Fe II strength (R_4570). To evaluate their accretion states, we derived single-epoch virial black hole masses using two approaches: an Fe II strength-dependent scaling relation and a recently established Eddington ratio-dependent fundamental plane. We further assessed how strongly the inferred accretion states depend on this choice by repeating the analysis with a conventional Fe II-independent calibration. The DESI-DR1 NLSy1 population occupies the extreme end of the EV1 parameter space, possessing strong Fe II emission (median R_ 4570 = 0.96 > 0); this fraction drops to sim8-9% with the Fe II-independent calibration and is therefore strongly calibration dependent. similar to that of the SDSS sample (0.96 /M_⊙ ≈ 6.81-6.85), and sim50% formally exceed the Eddington limit (łog λ_ Under both calibrations the two samples harbor low-mass black holes (median łog M_ BH ̊m Edd The unprecedented sensitivity of DESI has unveiled a large population of low-mass highly accreting NLSy1 galaxies. Under the high-accretion interpretation, the inner disk is expected to become geometrically thick and to shield the outer broad-line region, naturally producing the observed strong Fe II emission. This sample provides a rich statistical dataset of low-redshift candidate super-Eddington accretors, which can serve as laboratories for understanding early-Universe black hole growth.