首页> 外文期刊>The Astrophysical journal >The Neutral Interstellar Medium in Nearby Dwarf Galaxies. II. NGC 185, NGC 205, and NGC 147
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The Neutral Interstellar Medium in Nearby Dwarf Galaxies. II. NGC 185, NGC 205, and NGC 147

机译:附近矮星系中的中立星际介质。二。 NGC 185,NGC 205和NGC 147

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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.
机译:我们提供了两个矮椭圆形星系NGC 185和NGC 205中星际介质(ISM)的新的高分辨率观测结果,以及矮椭圆形星系NGC 147 HI含量的新上限。数据包括VLA观察到〜80 pc分辨率下的HI排放(比旧数据提高了3.5倍),NGC 185和NGC 205中〜80 pc分辨率下的CO光谱,NGC 205中40×20 pc分辨率的CO排放的图像BIMA阵列以及NGC 185和NGC 205的Hα图像。这些观察结果代表了两个独立的研究领域的交集:(1)巨型椭圆形中性气体的分布,运动学和起源,其结构与侏儒相似。椭圆形,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的物理特性,可以以很高的线性分辨率进行研究,但其星际介质可能与椭圆星系截然不同。新的H I图像显示NGC 205的中性气体和恒星是两个截然不同的动力学系统,而在NGC 185中,气体和恒星可能是同一动力学系统的一部分。这些星系中的H I分布比光学发射的扩展性小,并且似乎不是稳定的旋转圆盘,其结果与为巨型椭圆形建立的模式非常不同。对于NGC 185,内部气体起源(来自演化恒星的质量损失)可能是合理的。对于NGC 147,对于线宽为8 km s-1的未解析源,未检测到HI发射,上限为3×103M☉。 。此外,NGC 185和205中的H I分布在尺寸和质量尺度上都非常笨拙,小于200 pc和〜104M☉,H I速度分散范围为3至15 km s-1。我们提供的证据表明,这些星系中的分子气体与单个团块或原子气体云有关,类似于许多银河系巨分子云。但是,矮椭圆形中的H I列密度要比认为对银河系巨分子云屏蔽光解作用所必需的1021 cm-2小5-10倍。 Hα+ [N II]中NGC 185的图像显示了在银河系中心附近的直径50 pc的扩展发射区域和H I列密度峰值。

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