COSMOS-3D: Black Hole Mass Estimators and Luminosity Functions of Paschen-line AGNs
June 2026 • 2026ApJ..1004...92J
Abstract • Near-IR Paschen lines are potentially excellent tracers of Type 1 active galactic nuclei (AGNs) that is hardly affected by dust extinction. JWST allows us, for the first time, to explore Paschen-line objects at redshift z > 1. Here we present a study of 62 AGNs with broad Paα and Paβ lines at 1 < z < 3 using data from the JWST COSMOS-3D program. These AGNs are efficiently selected and identified using NIRCam imaging and grism slitless spectroscopic data. We separate the AGN-host emission with image decomposition and quantify dust attenuation with multiband data. We construct a calibration sample with optical spectroscopy and use single-epoch, Mg II-based black hole masses (MBH) as an anchor to derive new, Paschen-based MBH estimators. We obtain three sets of MBH estimators based on Paschen line luminosities and AGN continuum luminosities at 1 and 2 μm, respectively. After dust corrections, they are well consistent with each other, and also broadly agree with previous results. With this AGN sample, we further construct the first Paα and Paβ luminosity functions (LFs) of Type 1 AGNs. The derived LFs are 3─5 times higher than those of UV/optical-selected AGNs, indicating that Paschen-selected Type 1 AGNs are more complete. In addition, the intrinsic properties of our AGNs show no dependence on dust reddening, suggesting that the observed reddening is unrelated to the central engine and is thus likely caused by line-of-sight obscuration.
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