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(beta) 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 approximately 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).
Cristiani, S., Giallongo, E., Buson, L.m., Gouiffes, C., LA FRANCA, F. (1993). COORDINATED UV-OPTICAL OBSERVATIONS OF QUASARS - THE EVOLUTION OF THE LYMAN ABSORPTION. ASTRONOMY & ASTROPHYSICS, 268(1), 86-92.
COORDINATED UV-OPTICAL OBSERVATIONS OF QUASARS - THE EVOLUTION OF THE LYMAN ABSORPTION
LA FRANCA, Fabio
1993-01-01
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(beta) 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 approximately 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).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
