Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...417..528j&link_type=abstract
Astrophysical Journal v.417, p.528
Astronomy and Astrophysics
Astronomy
12
Galaxies: Intergalactic Medium, Galaxies: Quasars: General, Surveys, Ultraviolet: Galaxies
Scientific paper
We present the first results of an exploratory objective prism survey of the far-ultraviolet (λλ1200-1800) spectra of high-redshift quasars obtained with the Faint Object Camera on-board the Hubble Space Telescope. The prime objective of this survey is to identify one or more candidates among the known quasars at Ζem > 3 with sufficient flux at far-ultraviolet wavelengths to enable detailed follow-up observations of redshifted intergalactic He II λ304 absorption using the HST grating spectrographs FOC prism observations of 12 prime candidates selected for redshift (Ζem ≃ 3.03-3.66), brightness (V ≲ 18.5) and the appearance of their optical absorption spectra are presented and discussed. As anticipated beforehand, cumulative neutral hydrogen Lyman continuum absorption from the various classes of intervening absorption systems presents a serious obstacle for observing high redshift quasars at extreme ultraviolet rest energies. At our limiting sensitivity of Fλ ≃ 2-4 × 10-16 ergs s-1 cm-2 Å-1, 10 of the 12 objects observed show no far-UV flux shortward of λ1800 observed wavelength. Two objects, Q0114-089 (UM 670; Ζem ≃ 3.16) and Q1442+102 (OQ 172; Ζem = 3.53) are detected, but only down to 330 Å and 345 Å rest wavelength. No object is reliably detected at emitted He II λ304. The severity of the cumulative Lyman continuum absorption is, however, such that these preliminary findings are still statistically consistent with the hypothesis that luminous quasars are intrinsically bright at extreme ultraviolet energies at flux levels comparable to those suggested by extrapolation of the power law continua seen at longer wavelengths. A larger number of high-redshift quasars need to be observed in the far-UV before the prospects for observing intergalactic He II λ304 absorption with HST can be fully appraised.
Albrecht Roland
Barbieri Carlo
Baxter D.
Blades Chris J.
Boksenberg Alec
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