AI 中文总结
研究不同环境下星系氢原子盘大小，以AMIGA为对照样本，通过拟合椭圆计算氢原子直径，避免传统比值偏差，用基线残差量化截断，发现HCG星系氢原子盘明显小于孤立星系，截断随演化序列增加，与室女座星系团样本类似。
AI 中文摘要
氢原子的21厘米谱线是星系外盘的灵敏示踪剂，环境特征在那里最为明显。氢原子盘与光学盘的相对范围（$D_{\rm HI}$与$D_{25}$）被认为能定量衡量这种印记，但极端环境之间的系统比较仍然很少。我们使用AMIGA样本（一个能在最小外部影响下捕捉长期演化的对照样本）来量化希克森致密星系群（HCGs）中氢原子盘的相对范围。通过直接将椭圆拟合到$1\,M_{\odot}\,{\rm pc}^{-2}$等密度轮廓来计算氢原子直径。由于$D_{\rm HI}$和$D_{25}$是非线性相关的，我们避免使用传统的$D_{\rm HI}/D_{25}$比值（它存在与大小相关的偏差），而是将截断量化为孤立星系$D_{\rm HI}$-$D_{25}$基线的残差，通过贝叶斯分析为AMIGA建立该基线。完整分析以可重现的Python包和Snakemake工作流程提供。在$D_{\rm HI}$-$D_{25}$平面中，HCG星系系统地低于孤立星系基线。当将未检测到氢原子的成员作为上限包括在内时，HCGs的氢原子盘比相同光学直径的孤立星系预期的至少小约71%。截断沿着HCG演化序列从第1阶段到第3阶段单调增加。与文献样本的比较表明，HCGs处于截断最严重的一端，与室女座星系团样本（VIVA）在统计上无法区分。与AMIGA相比，在松散星系群、致密星系群和星系团落入/场环境中，氢原子盘相对于光学盘通常较小，在HCGs和室女座星系团样本中截断最为严重。
英文摘要
The 21 cm line of atomic hydrogen (HI) is a sensitive tracer of the outer disk of galaxies, where environmental signatures are most apparent. The relative extent of HI disks compared to optical disks ($D_{\rm HI}$ vs $D_{25}$) is thought to provide a quantitative measure of such imprint, yet systematic comparisons between extreme environments remain scarce. We quantify the relative extent of HI disks in Hickson Compact Groups (HCGs) and in the Analysis of the interstellar Medium in Isolated GAlaxies (AMIGA) sample, using AMIGA as a control sample that captures secular evolution with minimal external influence. We calculate HI diameters by directly fitting an ellipse to the $1\,M_{\odot}\,{\rm pc}^{-2}$ iso-density contour. Because $D_{\rm HI}$ and $D_{25}$ are nonlinearly related, we avoid the traditional $D_{\rm HI}/D_{25}$ ratio, which carries a size-dependent bias, and instead quantify truncation as the residual from the isolated-galaxy $D_{\rm HI}$-$D_{25}$ baseline, which we establish for AMIGA via Bayesian analysis. The full analysis is provided as a reproducible Python package and Snakemake workflow. HCG galaxies lie systematically below the isolated-galaxy baseline in the $D_{\rm HI}$-$D_{25}$ plane. When members with HI nondetections are included as upper limits, HCGs have HI disks at least ~71% smaller than expected for isolated galaxies of the same optical diameter. The truncation increases monotonically along the HCG evolutionary sequence, from Phase 1 to Phase 3. A comparison with literature samples places HCGs at the most-truncated end, statistically indistinguishable from the Virgo cluster sample (VIVA). Compared to AMIGA, HI disks are typically smaller relative to the optical disk in loose groups, compact groups, and cluster infall/field environments, and are most strongly truncated in HCGs and in the Virgo cluster sample.
Comments21 pages, 8 figures. Accepted for publication in Astronomy & Astrophysics. Analysis code and data: https://github.com/ianjarog/galaxydisksize ; online material: https://doi.org/10.5281/zenodo.21415323
