标题： 外部星系中HI 21厘米吸收强度与影响参数之间的相关性 显示英文标题

标题： A correlation between the HI 21-cm absorption strength and impact parameter in external galaxies

摘要： 通过结合附近星系中不同冲击参数下的HI 21厘米吸收的调查数据，我们发现21厘米吸收强度（速度积分光学深度）与冲击参数之间存在反相关关系。 此外，通过将21厘米吸收强度与发射强度相结合，得到中性氢柱密度，我们没有发现气体的自旋温度（与覆盖因子成正比）在盘面上有显著变化的证据。 这与银河盘面上测量到的自旋温度均匀性一致。 此外，与银河分布的比较表明，21厘米吸收更倾向于出现在高倾角（接近正面）的盘面中。 我们还研究了21厘米吸收更有可能在紧凑射电源方向上被探测到的假设。 尽管数据不足以确定在类星体视线还是射电星系视线中检测率更高，但21厘米检测到的对象平均转折频率为5 x 10^8 Hz，而非检测到的对象为1 x 10^8 Hz。 由于转折频率与射电源大小呈反相关，这确实表明检测更倾向于紧凑背景射电源。 所有 XMATHX 相关符号均保持原样。 显示英文摘要

摘要： By combining the data from surveys for HI 21-cm absorption at various impact parameters in near-by galaxies, we report an anti-correlation between the 21-cm absorption strength (velocity integrated optical depth) and the impact parameter. Also, by combining the 21-cm absorption strength with that of the emission, giving the neutral hydrogen column density, we find no evidence that the spin temperature of the gas (degenerate with the covering factor) varies significantly across the disk. This is consistent with the uniformity of spin temperature measured across the Galactic disk. Furthermore, comparison with the Galactic distribution suggests that intervening 21-cm absorption preferentially arises in disks of high inclinations (near face-on). We also investigate the hypothesis that 21-cm absorption is favourably detected towards compact radio sources. Although there is insufficient data to determine whether there is a higher detection rate towards quasar, rather than radio galaxy, sight-lines, the 21-cm detections intervene objects with a mean turnover frequency of 5 x 10^8 Hz, compared to 1 x 10^8 Hz for the non-detections. Since the turnover frequency is anti-correlated with radio source size, this does indicate a preferential bias for detection towards compact background radio sources.