We present a high signal-to-noise spectrum of a bright galaxy at z = 4.9 in 14 h of integration on VLT FORS2. This galaxy is extremely bright, i850 = 23:10 0:01, and is strongly-lensed by the foreground massive galaxy cluster Abell 1689 (z = 0:18). Stellar continuum is seen longward of the Ly emission line at 7100 A, while intergalactic H I produces strong absorption shortward of Ly. Two transmission spikes at 6800 A and 7040 A are also visible, along with other structures at shorter wavelengths. Although fainter than a QSO, the absence of a strong central ultraviolet ux source in this star forming galaxy enables a measurement of the H I ux transmission in the intergalactic medium (IGM) in the vicinity of a high redshift object. We find that the effective H I optical depth of the IGM is remarkably high within a large 14 Mpc (physical) region surrounding the galaxy compared to that seen towards QSOs at similar redshifts. Evidently, this high-redshift galaxy is located in a region of space where the amount of H I is much larger than that seen at similar epochs in the diffuse IGM. We argue that observations of high-redshift galaxies like this one provide unique insights on the nascent stages of baryonic large-scale structures that evolve into the filamentary cosmic web of galaxies and clusters of galaxies observed in the present universe.
Frye, Brenda L.; Bowen, David V.; Hurley, Mairead; Tripp, Todd M.; Fan, Xiaohui; Holden, Bradley; Guhathakurta, Puragra; Coe, Dan; Broadhurst, Tom; Egami, Eiichi; and Meylan, G., "Observations of the Gas Reservoir Around a Star Forming Galaxy In The Early Universe" (2008). Astronomy Department Faculty Publication Series. 22.