paper

X-ray and CO-Derived Column Densities in AGN: A Study of Obscuration Properties in CTAGN and Non-CTAGN

arXiv:2502.19059 · doi:10.1017/pasa.2025.22

Abstract

Obscuration in active galactic nuclei (AGN) provides insights into the material surrounding the central engine. Compton-thick AGN (CTAGN), characterized by a column density of , are heavily obscured by dust and gas. While X-ray observations primarily determine this column density, the sub-mm obscuration properties of CTAGN remain less explored. We analyze archival ALMA CO(3-2) data for CTAGN and non-CTAGN from the 70-month /BAT catalog and other X-ray surveys. Integrated intensity maps (moment 0) reveal dense gas concentrated around the nucleus. Assuming a constant CO-to- conversion factor, , we find that molecular hydrogen column densities () are generally lower than X-ray-derived total hydrogen column densities (). However, values in this work are slightly higher than in previous studies due to the adopted conversion factor. The discrepancy between and aligns with prior findings that X-ray-derived values tend to be higher, except for non-CTAGN, where can exceed . Kendall and Spearman tests indicate a positive monotonic correlation, though not statistically significant, suggesting a complex interplay of factors. The optically thick nature of CO in dense regions may contribute to the observed differences. Our results highlight the need for an accurate CO-to- conversion factor in deriving column densities, potentially offering an alternative method for identifying CTAGN. Future studies with larger datasets and refined methodologies are essential for a deeper understanding of sub-mm and X-ray properties in AGN.

arXiv commentThis paper has been accepted for publication in PASA

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