The Neutral Interstellar Medium in Nearby Dwarf Galaxies. II. NGC 185, NGC 205, and NGC 147
The Neutral Interstellar Medium in Nearby Dwarf Galaxies. II. NGC 185, NGC 205, and NGC 147
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附近矮星系中的中性星际介质。
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发表时间：
1997
期刊：
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通讯作者：
K. Lo
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作者：
L. M. Young;K. Lo
我们对两个矮椭圆星系NGC 185和NGC 205的星际介质（ISM）进行了新的高分辨率观测，并对矮椭圆星系NGC 147的H - I含量给出了新的上限。数据包括~ 80pc分辨率的VLA观测数据（比旧数据提高了3.5倍）、NGC 185和NGC 205 ~ 80pc分辨率的CO光谱、BIMA阵列40 × 20pc分辨率的NGC 205 CO发射图像以及NGC 185和NGC 205的Hα图像。这些观测结果代表了两个独立研究领域的交集：(1)巨椭圆中中性气体的分布、运动学和起源，巨椭圆在结构上与矮椭圆相似，但目前无法以如此高的线性分辨率进行研究；(2)银河系及其邻近星系中ISM的物理性质，可以用非常高的线性分辨率进行研究，但它们的星际介质可能与椭圆星系非常不同。新的H I图像显示NGC 205的中性气体和恒星是两个不同的动力系统，而NGC 185的气体和恒星可能是同一个动力系统的一部分。这些星系中的H I分布比光学发射的延伸要小，并且看起来不是稳定的旋转盘，这与为巨椭圆建立的模式非常不同。ngc185的内部气体起源（演化恒星的质量损失）可能是可信的。在NGC 147中没有探测到任何的氢辐射，其线宽为8 km s-1的未解析源的上限为3 × 103 M☉。此外，NGC 185和NGC 205的H分布在大小和质量尺度上都是非常团块的，小于200pc和~104 M☉，H速度弥散范围从3到15 km s-1。我们提供的证据表明，这些星系中的分子气体与原子气体的单个团块或云有关，类似于许多银河系巨型分子云。然而，矮椭圆中的H柱密度比1021 cm-2要小5-10倍，而1021 cm-2被认为是保护银河系巨分子云免受光解作用的必要条件。NGC 185在Hα + [N II]中的图像显示，在星系中心附近有一个直径为50pc的扩展发射区域和H I柱密度峰值。
We present new, high-resolution observations of the interstellar medium (ISM) in the two dwarf elliptical galaxies NGC 185 and NGC 205, as well as a new upper limit on the H I content of the dwarf elliptical galaxy NGC 147. The data consist of VLA observations of H I emission at ~80 pc resolution (a factor of 3.5 improvement over older data), CO spectra at ~80 pc resolution in NGC 185 and NGC 205, an image of CO emission in NGC 205 at 40 × 20 pc resolution from the BIMA array, and Hα images of NGC 185 and NGC 205. These observations represent the intersection of two separate fields of inquiry: (1) the distribution, kinematics, and origin of neutral gas in giant ellipticals, which are structurally similar to the dwarf ellipticals but cannot currently be studied at such high linear resolution; and (2) the physical properties of the ISM in the Galaxy and its neighbors, which can be studied at very high linear resolution but which might have very different interstellar media than elliptical galaxies. The new H I images show that the neutral gas and stars of NGC 205 are two distinct dynamical systems, whereas in NGC 185 the gas and stars may be parts of the same dynamical system. The H I distributions in these galaxies are less extended than the optical emission and do not appear to be stable rotating disks, a result that is very different from the pattern established for giant ellipticals. An internal gas origin (mass loss from evolved stars) may be plausible for NGC 185. No H I emission is detected in NGC 147 with an upper limit of 3 × 103 M☉ for an unresolved source with a line width of 8 km s-1. Furthermore, the H I distributions in NGC 185 and 205 are extremely clumpy on size and mass scales less than 200 pc and ~104 M☉, with H I velocity dispersions ranging from 3 to 15 km s-1. We present evidence that the molecular gas in these galaxies is associated with individual clumps or clouds of atomic gas, similar to many Galactic giant molecular clouds. However, the H I column densities in the dwarf ellipticals are factors of 5-10 less than the 1021 cm-2 thought to be necessary to shield Galactic giant molecular clouds against photodissociation. Images of NGC 185 in Hα + [N II] show an extended region of emission 50 pc in diameter near the center of the galaxy and the H I column density peak.