Discovery of 21cm absorption in a $z_{\mathrm{abs}}=2.289$ DLA towards TXS 0311+430: The first low spin temperature absorber at z > 1

Abstract

We report the detection of HI 21 cm absorption from the $z=2.289$ damped Lyman-$\alpha$ system (DLA) towards TXS 0311+430, with the Green Bank Telescope. The 21 cm absorption has a velocity spread (between nulls) of $\sim 110$ km s${}^{-1}$ and an integrated optical depth of $\int \tau \mathrm{d}V=(0.818\pm 0.085)$ km s${}^{-1}$. We also present new Giant Metrewave Radio Telescope 602 MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA HI column density of \nhi = $(2\pm 0.5)\times 10^{20}$ \cm, yields a spin temperature of $T_s=(138\pm 36)$ K, assuming a covering factor of unity. This is the first case of a low spin temperature ($<350$ K) in a $z>1$ DLA and is among the lowest ever measured in any DLA. Indeed, the $T_s$ measured for this DLA is similar to values measured in the Milky Way and local disk galaxies. We also determine a lower limit (Si/H) $\gtrsim 1/3$ solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low redshift correlations, the low $T_s$, large 21 cm absorption width and high metallicity all suggest that the $z\sim 2.289$ DLA is likely to arise in a massive, luminous disk galaxy.

5 pages, 3 figures. Accepted for publication in MNRAS (Letters)

References in corpus (5)

• The Ucsd/Keck Damped Lya Abundance Database: A Decade of High Resolution Spectroscopy
• The Metal-Strong Damped Lyman-alpha Systems
• HI 21cm Absorption at $z\sim 2.347$ towards PKS B0438-436
• HI 21cm absorption at $z\sim 3.39$ towards PKS 0201+113
• Detection of broad 21-cm absorption at z = 0.656 in the complex sight-line towards 3C336

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• Giant Metrewave Radio Telescope detection of two new HI 21cm absorbers at $z\approx 2$
• A statistical measurement of the HI spin temperature in DLAs at cosmological distances
• The evolution of cold neutral gas and the star formation history
• A search for H$\alpha$ emission in high-metallicity damped Lyman-$\alpha$ systems at $z\sim 2.4$
• The potential of tracing the star formation history with HI 21-cm in intervening absorption systems
• The Energetics of Launching the Most Powerful Jets in Quasars: A Study of 3C82
• The curious case of J113924.74+164144.0: a possible new group of galaxies at z = 0.0693