The Resolved Structure and Dynamics of an Isolated Dwarf Galaxy: A VLT and Keck Spectroscopic Survey of WLM
Ryan Leaman, Kim A. Venn, Alyson M. Brooks, Giuseppina Battaglia, Andrew A. Cole, Rodrigo A. Ibata, Mike J. Irwin, Alan W. McConnachie, J. Trevor Mendel, Eline Tolstoy
备注：
14 Pages, 17 figures, 3 tables. Accepted for publication in ApJ
本文给出了孤立矮不规则星系WLM中180颗红巨星分支星的光谱数据。在VLT的FORS 2和凯克II的DEIMOS上观测到了覆盖整个星系的RGB恒星光谱中的钙II三重线，使我们能够推导出恒星的速度、金属丰度和年龄。伴随着光度和无线电数据，我们已经测量了整个星系的恒星和气体种群的结构参数。恒星星族显示出一个固有的厚配置与$0.39 \leq q_{0} \leq 0.57$。WLM中的恒星自转被测量为$17 \pm 1$ km s $^{-1}$，然而恒星的自转与压力支持的比率为$V/σ\sim 1$，与气体的比率相比，气体的比率大7倍。这一点，以及结构数据和运动学和光度轴的对齐，表明我们正在查看WLM作为一个高度倾斜的扁球体。恒星自转曲线，校正不对称漂移，用于计算的动力学质量的$4.3\pm 0.3\times10^{8} $ M $_{\odot}$在半光半径（$r_{h} = 1656 \pm 49$ pc）。恒星的速度色散增加与恒星年龄的方式一致的巨型分子云和子结构的相互作用产生的加热WLM。再加上WLM的隔离，这表明其恒星和气体成分的延伸垂直结构和恒星速度色散随年龄的增加是由于内部反馈，而不是潮汐驱动的演化。这些代表了一些第一个观测结果，从一个孤立的本地集团矮星系，可以提供重要的约束如何强烈的内部反馈和长期的过程调制SF和动力学演化的低质量孤立的对象。
英文摘要：
We present spectroscopic data for 180 red giant branch stars in the isolated dwarf irregular galaxy WLM. Observations of the Calcium II triplet lines in spectra of RGB stars covering the entire galaxy were obtained with FORS2 at the VLT and DEIMOS on Keck II allowing us to derive velocities, metallicities, and ages for the stars. With accompanying photometric and radio data we have measured the structural parameters of the stellar and gaseous populations over the full galaxy. The stellar populations show an intrinsically thick configuration with $0.39 \leq q_{0} \leq 0.57$. The stellar rotation in WLM is measured to be $17 \pm 1$ km s$^{-1}$, however the ratio of rotation to pressure support for the stars is $V/σ\sim 1$, in contrast to the gas whose ratio is seven times larger. This, along with the structural data and alignment of the kinematic and photometric axes, suggests we are viewing WLM as a highly inclined oblate spheroid. Stellar rotation curves, corrected for asymmetric drift, are used to compute a dynamical mass of $4.3\pm 0.3\times10^{8} $M$_{\odot}$ at the half light radius ($r_{h} = 1656 \pm 49$ pc). The stellar velocity dispersion increases with stellar age in a manner consistent with giant molecular cloud and substructure interactions producing the heating in WLM. Coupled with WLM's isolation, this suggests that the extended vertical structure of its stellar and gaseous components and increase in stellar velocity dispersion with age are due to internal feedback, rather than tidally driven evolution. These represent some of the first observational results from an isolated Local Group dwarf galaxy which can offer important constraints on how strongly internal feedback and secular processes modulate SF and dynamical evolution in low mass isolated objects.
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University of California, Berkeley（加州大学伯克利分校）；Gemini Observatory / NSF’s NOIRLab（吉米天文台 / 美国国家光学红外天文研究实验室）；University of San Francisco（旧金山大学）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Institute for Astronomy, University of Hawaii（夏威夷大学天体物理研究所）；University of Pittsburgh（匹兹堡大学）；University of California, Los Angeles（加州大学洛杉矶分校）；Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo（东京大学理化学研究所木下伽利略宇宙物质起源研究机构）
