Kavli Affiliate: Luis Ho
| Summary:
We present a sample of 930 intermediate-mass black hole (IMBH) active galactic nuclei (AGNs) with black hole masses of $M_mathrmBH leqslant 2 times 10^6$ M$_odot$, uniformly selected from the Seventeenth Data Release of the Sloan Digital Sky Survey, based on the detection of broad H$α$ or H$β$ 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 $zleqslant0.57$, significantly improving upon previous studies that where generally limited to $zleqslant0.35$. 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 $λlambda2796,2803$ emission lines, including eight confirmed by independent DESI spectra. A preliminary analysis reveals a marked decline in both the maximum accretion rate ($L/L_mathrmEdd$) and broad H$α$ 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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