2017年IOAA理论第4题-21厘米HI星系巡天

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IOAA赛场上通常是使用英文回答问题，所以建议各位用英文回答本题

英文原题

(T4) 21-cm HI galaxy survey [10 marks]

A radio telescope is equipped with a receiver which can observe in a frequency range from 1.32 to 1.52 GHz. Its detection limit is 0.5 mJy per beam for a 1-minute integration time. In a galaxy survey, the luminosity of the HI spectral line of a typical target galaxy is 10²⁸ W with a linewidth of 1 MHz. For a large beam, the HI emitting region from a far-away galaxy can be approximated as a point source. The HI spin-flip spectral line has a rest-frame frequency of 1.42 GHz.

What is the highest redshift, z , of a typical HI galaxy that can be detected by a survey carried out with this radio telescope, using 1-minute integration time? You may assume in your calculation that the redshift is small and the non-relativistic approximation can be used. Note that 1 Jy = 10^-26 W m^-2 Hz^-1. [10]

中文翻译

21厘米HI星系巡天

一台射电望远镜的观测频率为1.32到1.52GHz。它在1分钟的积分时间内的探测极限为每波束0.5mJy。在一次星系巡天中，典型目标星系的HI谱线光度为10²⁸W，谱线宽度为1MHz。对于一个大的波束来说，来自遥远星系的HI辐射区域可以近似为点源。HI自旋翻转谱线具有1.42GHz的静止参考系频率。

使用这台射电望远镜进行星系巡天，可以探测到的典型HI星系的最高红移z是多少？在你的计算中，可以采用低红移情况下的非相对论近似。注意1Jy=10^-26Wm^-2Hz^-1。

（《天文爱好者》上给出的翻译是“星系寻天”，但是通常使用的翻译是“星系巡天”。对翻译有修改，特此标注。）