Deuterium Nucleosynthesis in AGN: Is D Cosmological? Original Research Article

Although deuterium is predicted to be primarily cosmological, D can also be produced by cosmic-ray or γ-ray spallation reactions - possibly between high energy jets and the surrounding gas in AGN. We used the Nobeyama mm array with a 3" resolution (200 pc) in April 2003 to search for any enhanced D from the DCN J = 2 – 1 line in the 45"×45" (3 kpc) circumnuclear region of the Seyfert galaxy NGC 1068. NGC 1068 is an optimal target because it has jets, starburst activity, a circumuclear molecular ring and molecular disk, dense optically thick concentrations of HCN, and a low-energy X-ray flux of 1042 erg/s (the highest X-ray flux of any galaxy in which HCN has been detected and the flux required to produce high D abundances). Although DCN is detected in most Galactic or LMC molecular clouds with optically thick HCN, we did not detect DCN with Srms = 11 mJy/beam or Trms = 35.6 mK. Thus our 3σ upper limits are S⩽ 33 mJy/beam or Tmb ⩽ 106.7 mK and DCN/HCN⩽ 0.0044. Using our 5260 reaction chemical network we estimate the underlying D/H⩽ 1.5×10−5 – less than or equal to but not greater than the local Galactic ISM D/H = 1.5 × 10−5. Thus there is no significant D production in the nuclear region of NGC 1068 and NGC 1068 has probably not had a recent period of activity with a γ-ray or cosmic-ray luminosity > 1042 erg/s. If jet-cloud nucleosynthesis produces significant amounts of D, then the D is either produced inside a very small nuclear region or transported outside the nuclear region whereby subsequent infall may continuously supply galactic nuclei with D. However, any enhanced D produced via spallation reactions would have been destroyed via astration due to the large AGN star formation rate. Our results are additional evidence that D is primarily cosmological and that AGN do not produce D.