[论文解读] Kinematics and physical conditions of HI in nearby radio sources. The last survey of the old Westerbork Synthesis Radio Telescope

F. M. Maccagni, R. Morganti+3 more|arXiv (Cornell University)|May 1, 2017

Astrophysics and Cosmic Phenomena被引用 31

一句话总结

本研究利用Westerbork综合孔径射电望远镜的最终调查数据，分析了248个附近射电源的中性氢（H I）速度场和物理条件。研究发现27%的源检测到H I吸收，其中特别是蓝移、不对称的轮廓在高射电功率和中红外明亮源中占主导，表明由年轻射电活动驱动的外流存在。

ABSTRACT

We present an analysis of the properties of neutral hydrogen (HI) in 248 nearby (0.0230$ mJy and for which optical spectroscopy is available. The observations were carried out with the Westerbork Synthesis Radio Telescope as the last large project before the upgrade of the telescope with phased array feed receivers (Apertif). The sample covers almost four orders of magnitude in radio power from $\log\,P_{ m 1.4 \,GHz}=22.5$ W Hz$^{-1}$ and $26.2$ W Hz$^{-1}$. We detect HI in absorption in $27\% \pm 5.5\%$ of the objects. The distribution and kinematics of the absorbing HI gas appear to depend on radio power, the properties of the radio continuum emission, and the dust content of the sources. Among the sources where HI is detected, gas with kinematics deviating from regular rotation is more likely found as the radio power increases. In these cases, the HI profile is often asymmetric with a significant blue-shifted component. This is particularly common for sources with $\log\,P_{ m 1.4 \, GHz}>24$ W Hz$^{-1}$, where the radio emission is small, possibly because these radio sources are young. The same is found for sources that are bright in the mid-infrared, i.e. sources rich in heated dust. In these sources, the HI is outflowing likely under the effect of the interaction with the radio emission. Conversely, in dust-poor galaxies, and in sources with extended radio emission, at all radio powers we only detect HI distributed in a rotating disk. Stacking experiments show that in sources for which we do not detect HI in absorption directly, the HI has a column density that is lower than $3.5 imes 10^{17} (T_{ m spin}/c_f)$ cm$^{-2}$. We use our results to predict the number and type of HI absorption lines that will be detected by the upcoming surveys of the Square Kilometre Array precursors and pathfinders (Apertif, MeerKAT, and ASKAP).

研究动机与目标

• 研究附近射电 loud AGN 中中性氢（H I）的运动学和物理条件，以理解反馈机制。
• 确定H I吸收特性与射电功率、射电形态及尘埃含量的相关性。
• 通过运动学分析评估H I在燃料供给或被活动核驱逐中的作用。
• 利用堆叠技术探测未检测到H I的源，设定低柱密度气体的上限。
• 预测未来SKA路径探测器调查（Apertif、MeerKAT、ASKAP）中H I吸收的检测率。

提出的方法

• 利用Westerbork综合孔径射电望远镜（WSRT）对248个射电源（S1.4GHz > 30 mJy，z < 0.25）开展大规模H I吸收调查。
• 分析H I吸收轮廓的运动学结构，包括不对称性、蓝移或红移的翼部以及线宽。
• 根据射电功率（log P1.4GHz = 22.5–26.2 W Hz⁻¹）、射电形态（紧凑型与扩展型）以及中红外亮度（MIR明亮型与尘埃贫乏型）对源进行分类。
• 对未检测到H I的源进行堆叠，假设自旋温度和光学厚度模型，设定H I柱密度的上限。
• 将结果与光学光谱及多波段数据（如SDSS、WISE）进行比较，评估尘埃含量和AGN活动。
• 以ATLAS3D样本的堆叠结果为参考，推断早期型星系中H I分布可能具有双峰性。

实验结果

研究问题

• RQ1 在涵盖广泛射电功率范围的附近射电源中，H I吸收的检测率是多少？
• RQ2 H I吸收线的运动学特征如何与射电功率、射电形态及尘埃含量相关？
• RQ3 H I轮廓中的蓝移或红移翼是否指示外流或预先存在的内流？
• RQ4 在未直接检测到吸收的源中，H I柱密度的上限是多少？
• RQ5 未来SKA路径探测器调查（Apertif、MeerKAT、ASKAP）在不同红移和射电功率范围内将如何检测H I吸收？

主要发现

• 在248个源中，H I吸收的检测率为27% ± 5.5%，检测范围覆盖从log P1.4GHz = 22.5到26.2 W Hz⁻¹的全部射电功率区间。
• 在log P1.4GHz > 24 W Hz⁻¹且具有紧凑射电形态的源中，检测到更多不对称、蓝移或红移的H I吸收线，表明其运动学状态受到扰动。
• 在MIR明亮源中，具有强蓝移翼的宽H I吸收线（FWHM > 300 km s⁻¹）较为常见，表明中性气体外流由年轻射电喷流驱动。
• 在宽H I吸收线中未检测到红移翼，支持外流而非预先存在的内流的解释。
• 对未检测到H I的源进行堆叠实验，设定H I柱密度上限为3.5 × 10¹⁷ (Tspin/cf) cm⁻²，暗示未检测源中气体含量极低或自旋温度较高。
• ATLAS3D堆叠参考结果显示出一个3σ的H I发射线，NH I ≈ 2.1 × 10¹⁹ cm⁻²，表明H I分布可能具有双峰性：要么可被吸收探测到，要么仅以极低柱密度气体形式存在。