Small Scale Structure in the Universe and the Distribution of Baryons at High Redshift

Details Small Scale Structure in the Universe and the Distribution of Baryons at High Redshift Small Scale Structure in the Universe and the Distribution of Baryons at High Redshift

1997-09-14

arxiv.org/abs/astro-ph/9709129v1

Astronomy and Astrophysics

Astrophysics

9 pages LATEX, with 8 PostScript figures, using conf_iap.sty. To appear in the Proceedings of the 13th IAP (Paris) Colloquium,

Scientific paper

We briefly discuss the relevance of Lyman alpha forest observations for measuring cosmological parameters, comparing the properties of high z QSO spectra with those of artifical spectra from hydrodynamic simulations, based on hierarchical cosmologies. In particular, we describe a measurement of the baryon content of the universe obtained by matching the average opacity of the Lyman alpha forest from simulations to the observed one from a new dataset observed with the Keck telescope. We then report on a search for possible small scale structure in the intergalactic medium which could be unresolved by current cosmological simulations. Observing column density gradients in the spectra of lensed QSOs we find the typical intergalactic gas cloud to be structureless down to at least the 4 % level, on scales of 0.1 kpc. Extending the study of lensed absorption to higher column densities we begin to sample the velocity field internal to high redshift galaxies. Remarkable differences in column density (of order 50 %) and projected velocity (tens of km/s) between lines of sight separated by only a few hundred parsecs are found, and we may be observing structure in the early interstellar medium.

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