The Compton-thick AGN population and the N_H distribution of low-mass AGN in our cosmic backyard

We present a census of the Compton-thick (CT) active galactic nucleus (AGN) population and the column density ( N_H ) distribution of AGN in our cosmic backyard using a mid-infrared selected AGN sample within 15 Mpc. The column densities are measured from broad-band X-ray spectral analysis, mainly using data from Chandra and NuSTAR . Our sample probes AGN with intrinsic 2-10 keV luminosities of L_2-10,int = 10³⁷ -10⁴³ erg s^-1, reaching a parameter space inaccessible to more distant samples. We directly measure a 32⁺³⁰_-18 per cent CT AGN fraction and obtain an N H distribution that agrees with that inferred by the Swift -BAT survey. Restricting the sample to the largely unexplored domain of low-luminosity AGN with L_{2-10, int} ≤ 10⁴² erg s^-1 , we found a CT fraction of 19^{+ 30}_-14 per cent, consistent with those observed at higher luminosities. Comparing the host-galaxy properties between the two samples, we find consistent star formation rates, though the majority of our galaxy have lower stellar masses (by ≈ 0.3 dex). In contrast, the two samples have very different black hole mass ( M_BH ) distributions, with our sample having ≈ 1.5 dex lower mean mass ( M_BH ∼ 10⁶ M⊙). Additionally, our sample contains a significantly higher number of LINERs and H II -type nuclei. The Eddington ratio range probed by our sample, ho we ver, is the same as Swift -BAT, although the latter dominates at higher accretion rates, and our sample is more evenly distributed. The majority of our sample with λ_Edd ≥ 10^-3 tend to be CT, while those with λ_Edd < 10^-3 are mostly unobscured or mildly obscured.