论文标题
Radyhift Active Garactic核中HI检测率的红移演变
Redshift evolution of the HI detection rate in radio-loud active galactic nuclei
论文作者
论文摘要
我们在29个无线电大通银河核（AGN）的样品中搜索相关的HI 21 cm吸收，价格为0.7 <Z <1 $，并使用升级的巨型Metrewave Radio Telescope进行。我们检测到HI 21厘米的吸收均未针对我们的目标AGN，获得了$3σ$上限的$ \ lyssim的光学深度$ \ lyssim $ 1％每50 km S $^{ - 1} $ CHANNEL。我们来源的无线电发光度低于大多数AGN在文献中类似的红移中搜索21 cm吸收的AGN，并且对于除两个目标以外的所有目标，紫外线的发光度低于阈值$ 10^{23} $ w hz $^hz $^{ - 1} $，上面是AGN环境中的HI，已完全建议使用。我们堆叠了HI光谱，以获得$ \ $ \ $ \ 0.17 $％的更严格限制，每50 km s $^{ - 1} $通道在样品的平均21 cm光学深度上。该样品以扩展的无线电来源为主，其中24个是在数十千座的尺度上扩展的。包括类似的扩展来源，$ 0.7 <z <z <1.0 $从文献中，与低点$ z $相比，我们发现在统计学上有意义（$ \ \ \3σ$）的证据表明，HI 21 cm吸收的强度在$ 0.7 <z <z <z <0.25 $ <0.25 $ <0.25 $ <0.25 $ <0.25 $ <0.25 $ <0.25 $ <0.25 $ <0.25 $ <0.25 $ < 1.0 $。 HI物理条件下的红移演变可能是由于高圆柱密度或高$ z $ agn环境中的高柱密度或高旋转温度，因此在高红移处较弱相关的HI 21 cm吸收。
We present a search for associated HI 21 cm absorption in a sample of 29 radio-loud active galactic nuclei (AGNs) at $0.7 < z < 1$, carried out with the upgraded Giant Metrewave Radio Telescope. We detect HI 21 cm absorption against none of our target AGNs, obtaining $3σ$ upper limits to the optical depth of $\lesssim$ 1% per 50 km s$^{-1}$ channel. The radio luminosity of our sources is lower than that of most AGNs searched for HI 21 cm absorption at similar redshifts in the literature, and, for all targets except two, the UV luminosity is below the threshold $10^{23}$ W Hz$^{-1}$, above which the HI in the AGN environment has been suggested to be completely ionised. We stacked the HI spectra to obtain a more stringent limit of $\approx 0.17$% per 50 km s$^{-1}$ channel on the average HI 21 cm optical depth of the sample. The sample is dominated by extended radio sources, 24 of which are extended on scales of tens of kiloparsecs. Including similar extended sources at $0.7 < z < 1.0$ from the literature, and comparing with a low-$z$ sample of extended radio sources, we find statistically significant ($\approx 3σ$) evidence that the strength of HI 21 cm absorption towards extended radio sources is weaker at $0.7<z<1.0$ than at $z < 0.25$, with a lower detection rate of HI 21 cm absorption at $0.7 < z < 1.0$. Redshift evolution in the physical conditions of HI is the likely cause of the weaker associated HI 21 cm absorption at high redshifts, due to either a low HI column density or a high spin temperature in high-$z$ AGN environments.
