HI and OH absorption in the lensing galaxy of MG J0414+0534

TL;DR

This study reports the detection of HI 21-cm absorption in a lensing galaxy at redshift 0.96, revealing details about the gas composition and suggesting the dust extinction occurs mainly in the quasar host galaxy.

Contribution

First detection of HI absorption in the lensing galaxy of MG J0414+0534, with analysis of molecular gas deficiency and implications for dust extinction origin.

Findings

Detected HI 21-cm absorption with two components separated by 0.4 arcsec.

Found a very low OH to HI column density ratio, indicating molecular gas underabundance.

Suggests optical-near-IR extinction is primarily in the quasar host galaxy, not the lens.

Abstract

We report the detection of \HI 21-cm absorption in the $z=0.96$ early-type lensing galaxy towards MG J0414+0534 with the Green Bank Telescope. The absorption, with total $N_{\rm HI}=1.6 \times 10^{18} (T_{\rm s}/f) {\rm cm}^{-2}$, is resolved into two strong components, probably due to the two strongest lens components, which are separated by 0.4\arcsec. Unlike the other three lenses which have been detected in \HI, J0414+0534 does not exhibit strong OH absorption, giving a OH/\HI column density ratio of $N_{\rm OH}/N_{\rm HI}\lapp10^{-6}$ (for $T_{\rm s}=100$ K, $T_{\rm x}=10$ K and $f_{\rm HI}=f_{\rm OH}=1$). This underabundance of molecular gas may indicate that the extreme optical--near-IR colour ($V-K=10.26$) along the line-of-sight is not due to the lens. We therefore suggest that despite the strong upper limits on molecular absorption at the quasar redshift, as traced by millimetre lines, the extinction occurs primarily in the quasar host galaxy.