[Previous] | [Session 35] | [Next]
D. Tytler, J.M. O'Meara, D. Lubin, N. Suzuki (UCSD), S. Burles (UCSD & Fermilab), D. Kirkman (UCSD & Bell Labs. Lucent Technologies)
We review the measurement of D/H using UV spectra of QSOs and Galactic stars. The primordial D/H was determined during big bang nucleosynthesis (BBN). In the standard theory, with a homogeneous universe and three neutrinos, the abundances of the light nuclei depend on only one parameter: the baryon to photon ratio. D/H is the most sensitive measure of this ratio, and also of the cosmological baryon density, because the photon density is well known from the Cosmic Microwave Background temperature. In 1994 our group began a large systematic search for QSOs which show D. We obtain D/H directly from the column densities of the Lyman series lines, where the D lines are 82 km/s to the blue of those of H. We have now measured D/H in three QSOs, while a fourth QSO gives a consistent stringent upper limit. Since the metal abundance in these instances is 0.01 solar and below, it is believed that we are seeing the primordial D/H. High signal to noise spectra (50 per 2 km/s) of many QSOs are needed to show that absorption lines are D and not H, which can often looks similar to D, and could be indistinguishable in some cases. The D/H in the local interstellar medium of our Galaxy is about half of the primordial value, indicating that half of all atoms have not been inside a star, where all of the D would have been destroyed. The FUSE satellite will produce orders of magnitude more data on the distribution of D/H in the ISM. When we divide the FUSE D/H by the primordial D/H, we will know the fraction of all atoms which were not in stars in a wide variety of locations. This ratio depends on the past star formation and the in-fall of less processed gas, and will be a fresh constraint on Galactic chemical evolution. This work is funded in part by G-NASA NAG5-3237, NSF AST-9420443 and AST-9900842.