Imaging the Forest of Lyman Limit Systems
Imaging the Forest of Lyman Limit Systems
复制标题
莱曼极限系统森林的成像
DOI：
10.1086/177707
复制
发表时间：
1996
期刊：
影响因子：
--
通讯作者：
D. Weinberg
中科院分区：
文献类型：
--
作者：
A. Gould;D. Weinberg
我们表明，它现在是可能的图像光学厚$\lya$云荧光$\lya$发射与一个相对较长的（$\sim 20 $hr）的大型（$\sim 10 $m）望远镜的整合。对于一个宽范围的柱密度（$N\gsim 10^{18.5} \cm^{-2}$），从复合级联的$\lya$光子的通量等于$\sim 0.6$倍的电离光子的通量，独立于云的几何形状。当碰撞激发是云的主要冷却机制时，会产生额外的光子。对于光学厚云中预期的典型物理条件，这些机制共同导致$\lya$发射通量是电离光子通量的$\sim（2/3）\VEV{\nu}/\nu_0$倍，其中$\VEV{\nu}$是电离背景光子的平均频率，$\nu_0$是莱曼极限频率。因此，从光学厚云（已知存在，例如，从类星体吸收线）给出了电离辐射背景能量的直接测量。此外，在同样的长狭缝光谱中，人们可以希望探测到来自其他$\sim 200$\lya$系统的辐射。这样的探测将允许人们制作一个二维的$\lya$森林地图。通过获取一系列这样的光谱，人们可以在三维空间中绘制森林，揭示高红移宇宙的结构。
We show that it is now possible to image optically thick $\lya$ clouds in fluorescent $\lya$ emission with a relatively long ($\sim 20 $hr) integration on a large ($\sim 10 $m) telescope. For a broad range of column densities ($N\gsim 10^{18.5} \cm^{-2}$), the flux of $\lya$ photons from recombination cascades is equal to $\sim 0.6$ times the flux of ionizing photons, independent of the geometry of the cloud. Additional $\lya$ photons are produced by collisional excitations when these are the cloud's primary cooling mechanism. For typical physical conditions expected in optically thick clouds, these mechanisms together lead to a $\lya$ emission flux that is $\sim (2/3) \VEV{\nu}/\nu_0$ times the flux of ionizing photons, where $\VEV{\nu}$ is the mean frequency of ionizing background photons and $\nu_0$ is the Lyman limit frequency. Hence, measurement of the surface brightness from an optically thick cloud (known to exist, e.g., from a quasar absorption line) gives a direct measure of the energy in the ionizing radiation background. Moreover, in the same long slit spectrum one could hope to detect emission from $\sim 200$ other $\lya$ systems. Such detections would allow one to make a 2-dimensional map of the $\lya$ forest. By taking a series of such spectra, one could map the forest in three dimensions, revealing structure in the high-redshift universe.