D. A. A. Lee | Searcharxiv

arXiv2026

The Neutral Hydrogen Gas Content of Star-forming and Quiescent S0 Galaxies

Lenticular (or S0) galaxies that remain actively star-forming (SFS0s) are a unique transition population among galaxies. We investigated the HI (21cm) neutral hydrogen content of a sample of lenticular galaxies identified from within the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey and which have been classified as star-forming or quiescent (qS0s). We compared these populations to each other and to a sample of star-forming spiral galaxies in MaNGA. We found that the HI Mass fraction and HI Deficiency of the SFS0s were intermediate between the quiescent S0s and the star-forming spirals, but most similar to the spirals. The HI depletion times of the quiescent S0's is very much longer than that of the SFS0 and spirals, which have roughly similar times. We also compared the molecular gas fractions of the three groups which shows that the lowest fraction of the three populations, followed by the star-forming S0s and then the star-forming spirals. A comparison of total baryonic mass comparisons indicates that the star-forming S0s have significantly lower masses than the qS0s in the sample. This suggests that the star-forming S0s must form from lower-mass progenitors (unobserved by MaNGA) which either accrete external gas, or loose spiral arms. The more massive quiescent S0s are a completely separate population, most likely to be formed either from fading star-forming spirals or from medium- to high-mass spirals undergoing mergers. The SFS0s in this sample cannot form from the quiescent S0s in this sample that receive in-falling gas, nor can they fade to create these qS0s.

astro-ph.GA↗

arXiv2025

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

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 $N_{\mathrm{H}} \geq 1.5 \times 10^{24} \ \mathrm{cm}^{-2}$, 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 $\textit{Swift}$/BAT catalog and other X-ray surveys. Integrated intensity maps (moment 0) reveal dense gas concentrated around the nucleus. Assuming a constant CO-to-$\mathrm{H_2}$ conversion factor, $X_{\mathrm{CO}} = 2.2 \times 10^{20} \ \mathrm{cm}^{-2} \ (\mathrm{K\ km\ s}^{-1})^{-1}$, we find that molecular hydrogen column densities ($N_{\mathrm{H_2}}$) are generally lower than X-ray-derived total hydrogen column densities ($N_{\mathrm{H}}$). However, $N_{\mathrm{H_2}}$ values in this work are slightly higher than in previous studies due to the adopted conversion factor. The discrepancy between $N_{\mathrm{H}}$ and $N_{\mathrm{H_2}}$ aligns with prior findings that X-ray-derived values tend to be higher, except for non-CTAGN, where $N_{\mathrm{H_2}}$ can exceed $N_{\mathrm{H}}$. 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-$\mathrm{H_2}$ 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.

astro-ph.GA↗