On the implausible physical implications of a claimed lensed neutral hydrogen detection at redshift z = 1.3

arXiv - PHYS - Cosmology and Nongalactic Astrophysics Pub Date : 2024-09-10 DOI:arxiv-2409.06812

Roger P. Deane, Tariq Blecher, Danail Obreschkow, Ian Heywood

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Abstract

The Square Kilometre Array mid-frequency array will enable high-redshift detections of neutral hydrogen (HI) emission in galaxies, providing important constraints on the evolution of cold gas in galaxies over cosmic time. Strong gravitational lensing will push back the HI emission frontier towards cosmic noon ($z\sim2$), as has been done for all prominent spectral lines in the interstellar medium of galaxies. Chakraborty & Roy (2023, MNRAS, 519, 4074) report a $z=1.3$ HI emission detection towards the well-modelled, galaxy-scale gravitational lens, SDSS J0826+5630. We carry out HI source modelling of the system and find that their claimed HI magnification, $\mu_{\rm HI} = 29 \pm 6$, requires an HI disk radius of $\lesssim 1.5$ kpc, which implies an implausible mean HI surface mass density in excess of $\Sigma_{\rm HI} > 2000$ M$_\odot$ pc$^{-2}$. This is several orders of magnitude above the highest measured peak values $(\Sigma_{\rm HI} \sim 10 \, {\rm M}_\odot\,{\rm pc}^{-2})$, above which HI is converted into molecular hydrogen. Our re-analysis requires this to be the highest HI mass galaxy known (M$_{\rm HI}~\sim 10^{11}$M$_\odot$), as well as strongly lensed, the latter having a typical probability of order 1 in 10$^{3-4}$. We conclude that the claimed detection is spurious.

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关于在红移 z = 1.3 处探测到有透镜的中性氢的难以置信的物理意义

平方公里阵列中频阵列将能够对星系中的中性氢（HI）发射进行高红移探测，为星系中的冷气体随宇宙时间的演化提供重要的约束条件。强引力透镜将把中性氢（HI）发射的前沿推向宇宙近期（$z\sim2$），就像星系星际介质中所有突出光谱线一样。Chakraborty & Roy（2023，MNRAS，519，4074）报告了对建模良好的星系尺度引力透镜SDSS J0826+5630的$z=1.3$ HI发射探测。我们对该系统进行了HI源建模，发现他们声称的HI放大率（$\mu_{\rm HI} = 29 \pm 6$）要求HI盘半径为$\lesssim 1.5$ kpc，这就意味着平均HI表面质量密度超过$\Sigma_{\rm HI} 是难以置信的。> 2000$ M$_\odot$pc$^{-2}$。这比测量到的最高峰值$(\Sigma_{rm HI} \sim 10 \, {\rm M}_\odot\,{\rm pc}^{-2})$高出几个数量级，超过这个数量级，HI就会转化为分子氢。我们的重新分析要求它是已知HI质量最高的星系（M$_{\rm HI}~\sim 10^{11}$M$_\odot$），而且是强透镜星系，后者的典型概率为1 in10$^{3-4}$。我们的结论是，声称的探测是虚假的。

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arXiv - PHYS - Cosmology and Nongalactic Astrophysics

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