A search for HeH+ and CH in a high-redshift QSO
  We performed a search for the HeH+ J=1-0 line (\nu_{rest} = 2010.183873 GHz) and simultaneously for the CH ^2\Pi_{3/2}(F_2)J=3/2 - ^2\Pi_{1/2}(F_2)J=1/2 lines (\nu_{rest}\approx 2006.8 and 2010.8 GHz) toward one of the highest-redshift quasars known, SDSS J114816.64+525150.3 (z= 6.4189). No clearly visible line was detected after obtaining an rms noise level of ~ 0.4 mK (~ 3 mJy) in 16 MHz (18 km s^{-1}) channels. At a level of 2.9sigma, however, there is a tentative emission feature shifted by about 100 km s^{-1} from the expected frequency of the HeH+ line. This shift is well within the width of the line profiles for CO and C+. The putative feature is about four times narrower than the previously detected CO and C+ lines. The difference in velocities as well as in the line widths could be explained by quite different conditions required for formation and excitation of HeH+ with respect to CO and C+. The HeH+ emission, if real, could probably arise in the dense ionized gas of this QSO. The velocity integrated flux in this tentative feature is 0.62 +/- 0.21 Jy km s^{-1} which corresponds to a total luminosity of L(HeH+)\approx 7.1 x 10^8 L_{sun}. As long as there is no independent confirmation, these values should be considered rather as upper limits. 
I. Zinchenko (1 and 2), V. Dubrovich (3) and C. Henkel (4) ((1)   Institute of Applied Physics of the Russian Academy of Sci...
astro-ph.CO