A Census of Active Galactic Nuclei Identified by the Mid-infrared [Ne v] Line at $\mathbf{z}\le 0.025$

Abstract

We present a census of local active galactic nuclei (AGN) at a redshift of $z\le 0.025$ selected using the high-ionization [Ne v] $\lambda 14.32\mu$m emission line from the Infrared Database of Extragalactic Observables from Spitzer (IDEOS). We identify 103 sources with detected [Ne v] emission, which we regard as AGN within the volume. This sample represents $\sim 18\%$ of the galaxy population within this redshift range, consistent with AGN fractions derived using other selection techniques. We investigate the biases and properties of this [Ne v]-selected AGN sample by comparing it with traditional AGN selection methods based on hard X-ray, optical, and mid-infrared colors. We find that our selection significantly misses AGN with underdeveloped narrow line regions (NLRs), which account for approximately half of the AGN identified by NLR-independent methods. However, approximately $\sim 10\%$ of our sample are undetected in optical diagnostics, while $\sim 40\%$ are missed by hard X-rays and $\sim 70\%$ by infrared continuum. Notably, $\sim 15\%$ of our AGN are missed by all classical methods, constituting a population of previously unidentified AGN revealed solely by the [Ne v] emission line. Based on our analysis, we show that this line can efficiently select heavily Compton-thick and host-dominated AGN systems. Our analysis also yields mean bolometric luminosities of $\log (L_{\mathrm{bol}}/\mathrm{erg}{\mathrm{s}}^{-1})=44.5\pm 0.7$, black hole masses of $\log (M_{\mathrm{BH}}/M_{\odot })=7.3\pm 0.6$, and Eddington ratio of ${\lambda }_{\mathrm{Edd}}=0.15\pm 0.11$. Our sample harbors AGN with comparable luminosities but systematically lower-mass black holes accreting at higher Eddington ratios than those in the hard X-ray-selected sample. This suggests that our AGN may represent local analogs of the rapidly growing SMBH population prevalent at cosmic noon.

24 pages, 8 figures, accepted for publication in ApJ