Imaging the Lyman-alpha Forest
Imaging the Lyman-alpha Forest
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莱曼阿尔法森林成像
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
D. Weinberg
中科院分区：
文献类型：
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作者：
A. Gould;D. Weinberg
We show that it is now possible to image optically thick Ly(cid:11) clouds in (cid:13)uores-cent Ly(cid:11) emission with a relatively long ((cid:24) 20hr) integration on a large ((cid:24) 10m) telescope. For a broad range of column densities (N > (cid:24) 10 18:5 cm (cid:0)2 ), the (cid:13)ux of Ly(cid:11) photons from recombination cascades is equal to (cid:24) 0:6 times the (cid:13)ux of ionizing photons, independent of the geometry of the cloud. Additional Ly(cid:11) 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 Ly(cid:11) emission (cid:13)ux that is (cid:24) (2=3)h(cid:23)i =(cid:23)0 times the (cid:13)ux of ionizing photons, where h(cid:23)i is the mean frequency of ionizing background photons and (cid:23)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 (cid:24) 200 other Ly(cid:11) systems. Such detections would allow one to make a 2-dimensional map of the Ly(cid:11) forest. By taking a series of such spectra, one could map the forest in three dimensions, revealing structure in the high-redshift universe. cloudlets) on the form of the 5, we the excitation Ly(cid:11) photon production, which depends primarily on total energy of the ionizing photons. We show that, for optically thick total Ly(cid:11) is to the total energy of the ionizing in x 6, we present a signal-to-noise estimate for a (cid:12)ducial
