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arXiv · 0706.2692

Detection of broad 21-cm absorption at z = 0.656 in the complex sight-line towards 3C336

S. J. Curran·P. Tzanavaris·M. T. Murphy·J. K. Webb·Y. M. Pihlstroem
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Abstract

We report the detection of 21-cm absorption at z = 0.656 towards 1622+238 (3C336). The line is very broad with a Full-Width Half Maximum (FWHM) of 235 km/s, giving a velocity integrated optical depth of 2.2 km/s. The centroid of the line is offset from that of the known damped Lyman-alpha absorption (DLA) system by 50 km/s, and if the Lyman-alpha and 21-cm absorption are due to the same gas, we derive a spin temperature of < 60 K, which would be the lowest yet in a DLA. The wide profile, which is over four times wider than that of any other DLA, supports the hypothesis that the hydrogen absorption is occurring either in the disk of a large underluminous spiral or a group of dim unidentified galaxies, associated with the single object which has been optically identified at this redshift.

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S. J. Curran, P. Tzanavaris, M. T. Murphy, J. K. Webb, Y. M. Pihlstroem. 2007-07-27. Detection of broad 21-cm absorption at z = 0.656 in the complex sight-line towards 3C336. https://doi.org/10.1111/j.1745-3933.2007.00354.x

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