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Coordinated UV-optical observations of quasars: the evolution of the Lyman absorption | | S. Cristiani
; E. Giallongo
; L. M. Buson
; C. Gouiffes
; F. La Franca
; | | Date: |
14 Oct 1992 | | Subject: | astro-ph | | Abstract: | The average flux decrement shortward the Ly$_{alpha}$ emission, due to the well-known ``forest’’ of absorptions, has been measured in the spectra of 8 quasars. Quasi-simultaneous optical and IUE observations of the two low redshift quasars PKS 0637--75 (z=0.654) and MC 1104+16 (z=0.632) have been carried out, obtaining relatively high S/N, spectrophotometrically calibrated data on their energy distribution from the rest frame H$_{eta}$ to the Lyman continuum. Six more quasars in the redshift range 2.5-3.4 have been observed in the optical domain. For all the quasars the ``intrinsic’’ continuum slope and normalization have been estimated longward the Ly$_{alpha}$ emission and extrapolated towards the Lyman continuum to measure the average depressions, which have been compared with the model statistics of the Ly$_{alpha}$ clouds. When all the known classes of absorbers are taken into account with plausible values for their equivalent width distribution and evolution, a good agreement is obtained with the observations. The results for the observed continuum decrement at $z sim 0.65$ are identical to those predicted by the evolution with redshift of the number of Ly$_{alpha}$ forest systems including the HST data and within $2sigma$ of the predicted value using the ``standard’’ Ly$_{alpha}$ evolution (as determined only at high z). | | Source: | arXiv, astro-ph/9210002 | | Services: | Forum | Review | PDF | Favorites | |
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