FAST-ASKAP 协同：量化 NGC 4636 群共存的潮汐剥离与冲压剥离
FAST-ASKAP Synergy: Quantifying Coexistent Tidal and Ram Pressure Strippings in the NGC 4636 Group
AI总结：
结合 FAST、ASKAP 和 ALFALFA 的 HI 数据，本研究开发了量化星系气体潮汐剥离与冲压剥离的参数，发现剥离现象在 NGC 4636 群中普遍存在，并提出了描述星系下落时 HI 丰度下降的经验模型与时标。
摘要：
结合来自 ASKAP WALLABY 和 FAST 协同巡天的新 HI 数据以及 ALFALFA 数据，我们研究了 NGC 4636 群中冲压剥离和潮汐相互作用的影响。我们开发了两个参数来量化和区分这两种效应对含 HI 星系气体剥离的影响：光学盘边缘的外力强度，以及 HI 盘剥离的由外向内程度。我们发现气体剥离在该群中很普遍，影响了 80% 的探测到 HI 的非并合星系，其中 41% 正在经历这两种类型的剥离。在同时经历这两种效应的星系中，这两种强度是独立的，而两种 HI 剥离程度之间呈现中等程度的负相关。两种强度均与 HI 盘收缩相关。当潮汐剥离起主导作用时，潮汐强度与低质量星系（$M_*<10^9\\,\text{M}_\odot$）相当均匀的变红有关。相比之下，冲压剥离与该群中星系颜色变化模式没有明确联系。结合这两种剥离程度，我们估算了总剥离程度，并提出一个经验模型，可以描述星系向群中心下落时 HI 丰度的下降。我们得出的剥离时标随距中心距离的增加而减小，从 $R_{200}$ 之外的 $\mathord{\sim}1\\,\text{Gyr}$ 到接近中心的 $\mathord{\lesssim}10\\,\text{Myr}$。对于富含 HI 的星系，自穿过 $2R_{200}$ 起约 $\mathord{\sim}3\\,\text{Gyr}$ 后发生气体耗尽，但对于贫 HI 星系则快得多。我们的结果以物理驱动的方式量化了环境效应驱动的星系演化的细节和过程，并可能有助于以观测方式分析流体动力学模拟。
英文摘要：
Combining new HI data from a synergetic survey of ASKAP WALLABY and FAST with the ALFALFA data, we study the effect of ram pressure and tidal interactions in the NGC 4636 group. We develop two parameters to quantify and disentangle these two effects on gas stripping in HI-bearing galaxies: the strength of external forces at the optical-disk edge, and the outside-in extents of HI-disk stripping. We find that gas stripping is widespread in this group, affecting 80% of HI-detected non-merging galaxies, and that 41% are experiencing both types of stripping. Among the galaxies experiencing both effects, the two types of strengths are independent, while two HI-stripping extents moderately anticorrelate with each other. Both strengths are correlated with HI-disk shrinkage. The tidal strength is related to a rather uniform reddening of low-mass galaxies ($M_*<10^9\,\text{M}_\odot$) when tidal stripping is the dominating effect. In contrast, ram pressure is not clearly linked to the color-changing patterns of galaxies in the group. Combining these two stripping extents, we estimate the total stripping extent, and put forward an empirical model that can describe the decrease of HI richness as galaxies fall toward the group center. The stripping timescale we derived decreases with distance to the center, from $\mathord{\sim}1\,\text{Gyr}$ beyond $R_{200}$ to $\mathord{\lesssim}10\,\text{Myr}$ near the center. Gas-depletion happens $\mathord{\sim}3\,\text{Gyr}$ since crossing $2R_{200}$ for HI-rich galaxies, but much quicker for HI-poor ones. Our results quantify in a physically motivated way the details and processes of environmental-effects-driven galaxy evolution, and might assist in analyzing hydrodynamic simulations in an observational way.
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