The Evolutionary Pathway of Low-mass Supermassive Black Holes at Intermediate Redshift: Insights from the JADES Survey

Understanding the relationship between supermassive black holes (SMBHs) and their host galaxies at different redshifts is crucial for unraveling the processes of SMBH–galaxy coevolution. We present the properties of nine type 1 active galactic nuclei (AGNs) at intermediate redshift (2 < z < 4) using the JWST Advanced Deep Extragalactic Survey. All of them show the significant H α broad line and the AGN contribution in spectral energy distribution. Our sample covers SMBH masses of 10 6.1−8.2 M ⊙ and stellar masses of 10 9.3−11.0 M ⊙ , comparable to those of the AGNs observed in the local Universe. In the low-mass SMBH regime (<10 8 M ⊙ ), the black hole (BH)-to-stellar mass ratios in our sample (0.01%–0.1%) differ from those of the AGNs at z > 4 (1%–10%), suggesting that BHs and galaxies may trace different evolutionary pathways at intermediate and high redshifts. We also perform 2D image decomposition using GALFIT to constrain the bulge mass by evaluating the bulge contribution in the rest-frame near-infrared flux. We identify the AGNs with low BH-to-bulge mass ratios compared to those observed in the nearby bulge-dominant galaxies. This finding suggests the existence of a galaxy-first evolutionary path, in which bulge formation occurs before substantial gas is efficiently accreted onto the central engine.