揭示侧视盘星系中复杂速度分布的起源
Uncovering the origin of complex velocity distributions in edge-on disc galaxies
AI总结：
本研究揭示侧视盘星系中多峰恒星视线方向速度分布源于旋臂，发现负$h_4$可示踪旋臂，指出高分辨率摄谱仪有望用于表征这类星系的旋臂。
摘要：
恒星视线方向速度分布（LOSVD）是研究星系运动学和形成历史的有力工具，多峰LOSVD通常表明存在复杂的运动学成分。我们提取了一个侧视模拟旋涡星系盘上的恒星LOSVD，研究多峰LOSVD出现的频率及原因。我们发现多峰LOSVD主要出现在银盘 midplane（ midplane 译为“银道面”）附近，因为它们由旋臂的存在导致；这并非因为旋臂与银盘有显著不同的运动学特性，而是因为旋臂对应着密度过高的区域。视线方向上旋臂数量的变化会导致LOSVD峰数的变化，这可用于量化银道面上方旋臂的强度，以及旋臂厚度在银盘上的变化情况。我们发现常用的四阶高斯-厄米特矩$h_4$在多峰LOSVD所在区域为负值，因此可用于示踪旋臂。最后，我们讨论了当前积分场摄谱仪对多峰区域及其相关$h_4$测量的可观测性：我们发现MUSE的光谱分辨率可能不足以揭示旋臂导致的LOSVD多峰，但应能识别负$h_4$区域；另一方面，KOALA和WEAVE等更高分辨率的摄谱仪或许能恢复LOSVD的多峰，这为表征侧视盘星系的旋臂提供了有前景的途径。
英文摘要：
Stellar line-of-sight velocity distributions are a powerful tool for studying galaxy kinematics and formation history, with multiple-peaked LOSVDs often indicating the presence of complex kinematic components. We extract stellar LOSVDs across the disc of a simulated spiral galaxy viewed edge-on, and study how often and why we see multiple-peaked LOSVDs. We find that the multiple-peaked LOSVDs are mainly found close to the midplane because they result from the presence of spiral arms. This is not because the spiral arms have significantly different kinematics to the disc, but because they correspond to over-densities. Variations in the number of arms present along a line-of-sight create variations in the number of peaks in LOSVDs. This can be used to quantify the strength of the spiral arms above the midplane, and how the thickness of spiral arms vary across the disc. We find that the commonly used fourth order Gauss-Hermite moment, $h_4$, is negative in the regions where there are multiple-peaked LOSVDs, and hence traces spiral arms. Finally, we discuss the observability of the multiple-peaked regions and their associated $h_4$ measurements with current integral field spectrographs. We find that the spectral resolution of MUSE might not be high enough to uncover multiple peaks in LOSVDs when they result from spiral arms, but should allow for identification of the regions of negative $h_4$. On the other hand, higher resolution spectrographs like KOALA and WEAVE may be able to recover multiple peaks in LOSVDs, representing a promising avenue for characterising spiral arms in edge-on disc galaxies.
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