The Compton-thick AGN Population and the $N_{\rm H}$ Distribution of Low-mass AGN in our Cosmic Backyard
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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| author | Annuar, A. Alexander, D. M. Gandhi, P. Lansbury, G. B. Rosli, M. N. Stern, D. Asmus, D. Ballantyne, D. R. Baloković, M. Bauer, F. E. Boorman, P. G. Brandt, W. N. Brightman, M. Chen, C. T. J. Del Moro, A. Farrah, D. Harrison, F. A. Koss, M. J. Lanz, L. Marchesi, S. Mohanadas, P. Nardini, E. Ricci, C. Zappacosta, L. |
| author_facet | Annuar, A. Alexander, D. M. Gandhi, P. Lansbury, G. B. Rosli, M. N. Stern, D. Asmus, D. Ballantyne, D. R. Baloković, M. Bauer, F. E. Boorman, P. G. Brandt, W. N. Brightman, M. Chen, C. T. J. Del Moro, A. Farrah, D. Harrison, F. A. Koss, M. J. Lanz, L. Marchesi, S. Mohanadas, P. Nardini, E. Ricci, C. Zappacosta, L. |
| contents | We present a census of the Compton-thick (CT) active galactic nucleus (AGN) population and the column density ($N_{\rm{H}}$) distribution of AGN in our cosmic backyard using a mid-infrared selected AGN sample within 15 Mpc. The column densities are measured from broadband X-ray spectral analysis, mainly using data from $\textit{Chandra}$ and $\textit{NuSTAR}$. Our sample probes AGN with intrinsic 2-10 keV luminosities of $L_{\rm 2-10, int} = 10^{37}$-$10^{43}$ erg s$^{-1}$, reaching a parameter space inaccessible to more distant samples. We directly measure a 32$^{+30}_{-18}\%$ CT AGN fraction and obtain an $N_{\rm{H}}$ distribution that agrees with that inferred by the $\textit{Swift}$-BAT survey. Restricting the sample to the largely unexplored domain of low-luminosity AGN with $L_{\rm 2-10, int}$ $\leq$ $10^{42}$ erg s$^{-1}$, we found a CT fraction of 19$^{+30}_{-14}\%$, 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 $\approx 0.3$ dex). In contrast, the two samples have very different black hole mass ($M_{\rm BH}$) distributions, with our sample having $\approx$1.5 dex lower mean mass ($M_{\rm BH}$ $\sim$ 10$^{6}$ $M_\odot$). Additionally, our sample contains a significantly higher number of LINERs and H$_{\rm{II}}$-type nuclei. The Eddington ratio range probed by our sample, however, is the same as $\textit{Swift}$-BAT, although the latter dominates at higher accretion rates, and our sample is more evenly distributed. The majority of our sample with $λ_{\rm Edd} \ge$ 10$^{-3}$ tend to be CT, while those with $λ_{\rm Edd} <$ 10$^{-3}$ are mostly unobscured or mildly obscured. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2506_08527 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The Compton-thick AGN Population and the $N_{\rm H}$ Distribution of Low-mass AGN in our Cosmic Backyard Annuar, A. Alexander, D. M. Gandhi, P. Lansbury, G. B. Rosli, M. N. Stern, D. Asmus, D. Ballantyne, D. R. Baloković, M. Bauer, F. E. Boorman, P. G. Brandt, W. N. Brightman, M. Chen, C. T. J. Del Moro, A. Farrah, D. Harrison, F. A. Koss, M. J. Lanz, L. Marchesi, S. Mohanadas, P. Nardini, E. Ricci, C. Zappacosta, L. Astrophysics of Galaxies High Energy Astrophysical Phenomena We present a census of the Compton-thick (CT) active galactic nucleus (AGN) population and the column density ($N_{\rm{H}}$) distribution of AGN in our cosmic backyard using a mid-infrared selected AGN sample within 15 Mpc. The column densities are measured from broadband X-ray spectral analysis, mainly using data from $\textit{Chandra}$ and $\textit{NuSTAR}$. Our sample probes AGN with intrinsic 2-10 keV luminosities of $L_{\rm 2-10, int} = 10^{37}$-$10^{43}$ erg s$^{-1}$, reaching a parameter space inaccessible to more distant samples. We directly measure a 32$^{+30}_{-18}\%$ CT AGN fraction and obtain an $N_{\rm{H}}$ distribution that agrees with that inferred by the $\textit{Swift}$-BAT survey. Restricting the sample to the largely unexplored domain of low-luminosity AGN with $L_{\rm 2-10, int}$ $\leq$ $10^{42}$ erg s$^{-1}$, we found a CT fraction of 19$^{+30}_{-14}\%$, 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 $\approx 0.3$ dex). In contrast, the two samples have very different black hole mass ($M_{\rm BH}$) distributions, with our sample having $\approx$1.5 dex lower mean mass ($M_{\rm BH}$ $\sim$ 10$^{6}$ $M_\odot$). Additionally, our sample contains a significantly higher number of LINERs and H$_{\rm{II}}$-type nuclei. The Eddington ratio range probed by our sample, however, is the same as $\textit{Swift}$-BAT, although the latter dominates at higher accretion rates, and our sample is more evenly distributed. The majority of our sample with $λ_{\rm Edd} \ge$ 10$^{-3}$ tend to be CT, while those with $λ_{\rm Edd} <$ 10$^{-3}$ are mostly unobscured or mildly obscured. |
| title | The Compton-thick AGN Population and the $N_{\rm H}$ Distribution of Low-mass AGN in our Cosmic Backyard |
| topic | Astrophysics of Galaxies High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2506.08527 |