Search for LiH in the ISM towards B0218+357

F. Combes and T. Wiklind
DEMIRM, Observatoire de Paris, 61 Av. de l'Observatoire, F-75014 Paris, France
Onsala Space Observatory, S-43992 Onsala, Sweden
Abstract: We report a tentative detection with the IRAM 30-m telescope of the LiH molecule in absorption in front of the lensed quasar B0218+357 (Fig. 3). We have searched for the rotational line of lithium hydride at 444 GHz (redshifted to 263 GHz). The line, if detected, is optically thin, very narrow, and corresponds to a column density of N(LiH) = 1.6 10 cm for an assumed excitation temperature of 15 K, or a relative abundance LiH/H 3 10 . We discuss the implications of this result.

  
Figure: Spectrum of LiH in its fundamental line (1-0) at 444 GHz, redshifted at 263 GHz, in absorption towards B0218+357, compared to the highly optically thick CO(2-1) line previously detected. The tentative LiH line is slightly shifted from the center by about 5km/s, but is still comprised within the CO(2-1) velocity range. Its width is compatible with what is expected from an optically thin line. Spectra have been normalised to the absorbed continuum level and the velocity resolution is 2.3 km/s

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