A spectroscopic study of UM 673 A and B - On the size of Lyman-alpha clouds

in Astrophysical Journal (1992), 389

The Ly-alpha forest spectra obtained for the A and B images of the gravitationally lensed high-redshift quasar UM 673 are investigated, and higher resolution data of the brightest (A) image are presented ... [more ▼]

The Ly-alpha forest spectra obtained for the A and B images of the gravitationally lensed high-redshift quasar UM 673 are investigated, and higher resolution data of the brightest (A) image are presented. In the 2-A resolution spectra, all the absorption lines detected at 5 sigma in the spectrum of the fainter B image are present in the A image, but two anticoincidences, i.e., two lines in A which do not have a counterpart in B at more than a 3-sigma confidence level, are detected. Given the fact that corresponding Ly-alpha lines in the spectra of A and B have their equivalent widths well correlated, this proves that both light beams actually cross the same clouds. Most of the velocity differences between corresponding lines are compatible with 0 km/s within the error bars, with a standard deviation of 17 km/s. For the two major heavy-element systems detected in the spectrum of UM 673, no significant difference between the corresponding lines in the two spectra are found. [less ▲]