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

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.

5 pages, 3 figures, accepted by MNRAS Letters

References in corpus (5)

• A survey for redshifted molecular and atomic absorption lines I
• Probing variations in fundamental constants with radio and optical quasar absorption-line observations
• HI 21cm Absorption at $z\sim 2.347$ towards PKS B0438-436
• HI 21cm absorption at $z\sim 3.39$ towards PKS 0201+113
• The detectability of HI 21-cm absorption in damped Lyman-alpha systems

Cited by in corpus (5)

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• Relationships between the HI 21-cm line strength, MgII equivalent width and metallicity in damped Lyman-alpha absorption systems
• Incidence of HI 21-cm absorption in strong FeII systems at $0.5<z<1.5$
• The potential of tracing the star formation history with HI 21-cm in intervening absorption systems