HALOGAS：盘星系面外HI的性质
HALOGAS: the properties of extraplanar HI in disc galaxies
摘要：
我们提出了一个系统的研究面外气体（EPG）的样本中的15个附近的晚型星系在中间倾角使用公开的，深干涉HI数据的HALOGAS调查。对于每一个系统，我们掩盖了HI发射来自定期旋转的磁盘，并使用合成数据立方体来模拟剩余的“异常”HI通量。我们的模型由一个光滑的，轴对称的厚组件描述的3个结构和4运动学参数，这是适合通过贝叶斯MCMC方法的数据。我们发现，面外HI是几乎无处不在的盘星系，因为我们没有检测到它只有两个系统的空间分辨率最差。EPG组件包含总HI质量的~5-25%，平均值为14%，并且具有几kpc的典型厚度，与基于流体静力平衡模型的预期不一致。EPG运动学在整个样本中非常相似，包括典型垂直梯度约为-10 km/s/kpc的滞后旋转，15-30 km/s的速度色散，以及对于大多数星系，垂直和径向方向的速度为20-30 km/s的全球流入。EPG HI质量与由恒星反馈提供动力的银河喷泉的简单模型的预测非常一致。光电离和相互作用的喷泉材料与环星系介质的组合效应可以定性地解释EPG的运动学，但需要银河喷泉的动力学模型来充分测试这个框架。
英文摘要：
We present a systematic study of the extraplanar gas (EPG) in a sample of 15 nearby late-type galaxies at intermediate inclinations using publicly available, deep interferometric HI data from the HALOGAS survey. For each system we mask the HI emission coming from the regularly rotating disc and use synthetic datacubes to model the leftover "anomalous" HI flux. Our model consists of a smooth, axisymmetric thick component described by 3 structural and 4 kinematical parameters, which are fit to the data via a Bayesian MCMC approach. We find that extraplanar HI is nearly ubiquitous in disc galaxies, as we fail to detect it in only two of the systems with the poorest spatial resolution. The EPG component encloses ~5-25% of the total HI mass, with a mean value of 14%, and has a typical thickness of a few kpc, incompatible with expectations based on hydrostatic equilibrium models. The EPG kinematics is remarkably similar throughout the sample, and consists of a lagging rotation with typical vertical gradients of about -10 km/s/kpc, a velocity dispersion of 15-30 km/s and, for most galaxies, a global inflow in both the vertical and radial directions with speeds of 20-30 km/s. The EPG HI masses are in excellent agreement with predictions from simple models of the galactic fountain powered by stellar feedback. The combined effect of photo-ionisation and interaction of the fountain material with the circumgalactic medium can qualitatively explain the kinematics of the EPG, but dynamical models of the galactic fountain are required to fully test this framework.
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