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arXiv · 0808.0921

Observations of the Gas Reservoir around a Star Forming Galaxy in the Early Universe

Brenda L. Frye·David. V. Bowen·Mairead Hurley·Todd M. Tripp·Xiaohui Fan·Bradley Holden·Puragra Guhathakurta·Dan Coe·Tom Broadhurst·Eiichi Egami·G. Meylan
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Abstract

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, i_850 = 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-alpha emission line at ~7100 Å, while intergalactic H I produces strong absorption shortward of Ly-alpha. Two transmission spikes at ~6800 Angstroms (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 flux source in this star forming galaxy enables a measurement of the H I flux 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.

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Brenda L. Frye, David. V. Bowen, Mairead Hurley, Todd M. Tripp, Xiaohui Fan, Bradley Holden, Puragra Guhathakurta, Dan Coe, Tom Broadhurst, Eiichi Egami, G. Meylan. 2008-08-08. Observations of the Gas Reservoir around a Star Forming Galaxy in the Early Universe. https://doi.org/10.1086/592273

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