标题： 高分辨率的致密高运动速度云成像 显示英文标题

标题： High-resolution imaging of compact high-velocity clouds

摘要： Braun和Burton（1999）识别出的紧凑孤立高亮度HI云团（CHVCs）中有六个例子被WSRT成像观测。 这65个确认的天体构成了一个动力学冷系统，在本星系群标准参考框架下速度弥散度的全局最小值仅为70 km/s，而同时以100 km/s的速度向本星系群质心方向下落。 这些天体具有特征性形态，其中几个致密的核心嵌入在一个弥散的晕中。 致密核心通常占HI线总流量的40%，覆盖源面积的大约15%。 这些核心是HI的冷凝聚相，即CNM，温度接近100 K，而晕则似乎是一层屏蔽柱状的温弥漫HI，即WNM，温度接近8000 K。 我们检测到一个具有迄今观测到最窄HI发射线之一的核心，其固有FWHM为2 km/s，亮度为75 K。 通过柱密度和体积密度的比较，我们得出的距离范围为0.5到1 Mpc。 对于同一个天体，我们确定其金属丰度为太阳的0.04至0.07倍。 通过要求具有多个核心的天体稳定性，可以推导出类似的高度距离，这些天体在30弧分尺度上显示出高达70 km/s的相对速度。 许多致密核心沿其椭圆扩展的主要轴显示出系统性的速度梯度，与圆周旋转一致。 几条推导出的旋转曲线可以用Navarro、Frenk和White（1997）提出的冷暗物质分布很好地拟合。 这些运动学特征表明，对于D=0.7Mpc的情况，暗物质与可见物质的质量比为10-50，并且该比例随距离D的倒数变化。 暗示的暗物质晕在每个源的中心2 kpc（10弧分）范围内主导了质量体积密度，提供了足够的静水压力以允许局部CNM凝聚。 （摘要） 显示英文摘要

摘要： Six examples of the compact, isolated high-velocity HI clouds (CHVCs) identified by Braun and Burton (1999) have been imaged with the WSRT. The 65 confirmed objects in this class define a dynamically cold system, with a global minimum for the velocity dispersion of only 70 km/s, found in the Local Group Standard of Rest, while in-falling at 100 km/s toward the LG barycenter. These objects have a characteristic morphology, in which several compact cores are embedded in a diffuse halo. The compact cores typically account for 40% of the HI line flux while covering some 15% of the source area. The cores are the cool condensed phase of HI, the CNM, with temp. near 100 K, while the halos appear to be a shielding column of warm diffuse HI, the WNM, with temp. near 8000 K. We detect a core with one of the narrowest HI emission lines ever observed, with intrinsic FWHM of 2 km/s and 75 K brightness. From a comparison of column and volume densities we derive a distance in the range 0.5 to 1 Mpc. We determine a metallicity for this same object of 0.04 to 0.07 solar. Comparably high distances are implied by demanding the stability of objects with multiple cores, which show relative velocities as large as 70 km/s on 30 arcmin scales. Many compact cores show systematic velocity gradients along the major axis of their elliptical extent which are consistent with circular rotation. Several of the derived rotation curves are well-fit by Navarro, Frenk, and White (1997) cold dark matter profiles. These kinematic signatures imply a high dark-to-visible mass ratio of 10-50, for D=0.7Mpc, which scales as 1/D. The implied dark matter halos dominate the mass volume density within the central 2 kpc (10 arcmin) of each source, providing a sufficent hydrostatic pressure to allow local CNM condensation. (abridged)