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arXiv · 2503.12898

A Sample of Active Galactic Nuclei with Intermediate-mass Black Holes Extended to $z \approx$ 0.6

Wen-Juan Liu·Luis C. Ho·Xiao-Bo Dong·Su Yao·Paulina Lira·Yicheng Guo
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Abstract

We present a sample of 930 intermediate-mass black hole (IMBH) active galactic nuclei (AGNs) with black hole masses of $M_\mathrm{BH} \leqslant 2 \times 10^{6}$ M$_{\odot}$, uniformly selected from the Seventeenth Data Release of the Sloan Digital Sky Survey, based on the detection of broad H$\alpha$ or H$\beta$ emission lines. Taking advantage of the wide wavelength coverage of BOSS/eBOSS spectroscopy, our sample extends the redshift coverage of low-$z$ IMBH AGNs to $z\leqslant0.57$, significantly improving upon previous studies that where generally limited to $z\leqslant0.35$. This sample encompasses black hole masses from $10^{4.0}$ to $10^{6.3}$ M$_{\odot}$, with Eddington ratios ranging from 0.01 to 1.9. Among the $z>0.3$ subset, 24 sources exhibit detectable broad Mg II $\lambda\lambda2796,2803$ emission lines, including eight confirmed by independent DESI spectra. A preliminary analysis reveals a marked decline in both the maximum accretion rate ($L/L_\mathrm{Edd}$) and broad H$\alpha$ luminosity with decreasing redshift, possibly reflecting a cosmic evolution of accretion activity at the low-mass end, akin to the ``downsizing'' evolutionary trend seen in high-mass AGNs.

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Wen-Juan Liu, Luis C. Ho, Xiao-Bo Dong, Su Yao, Paulina Lira, Yicheng Guo. 2025-03-17. A Sample of Active Galactic Nuclei with Intermediate-mass Black Holes Extended to $z \approx$ 0.6. https://doi.org/10.3847/1538-4365%2Fae64eb

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