Detection of the Intergalactic Medium Using Gunn-Peterson HEII304A Absorption in QSOS, and Far UV Spectra (cycle 4, High, GO-5492)

Details Detection of the Intergalactic Medium Using Gunn-Peterson HEII304A Absorption in QSOS, and Far UV Spectra (cycle 4, High, GO-5492) Detection of the Intergalactic Medium Using Gunn-Peterson HEII304A Absorption in QSOS, and Far UV Spectra (cycle 4, High, GO-5492)

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994hst..prop.5492t&link_type=abstract

HST Proposal ID #5492

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Hst Proposal Id #5492 Quasars &Amp, Agn Quasar Absorption

Scientific paper

FOS ultraviolet spectra will be obtained of two high zem QSOs which we have recently detected at 1400A with the FOC. One is the only QSO known which has sufficient ultraviolet flux for FOS spectra at wavelengths below HeII 304. The detection of Gunn-Peterson absorption by the Helium II Lyman-Alpha line at 304A, one of the most exciting prospects of the HST, will provide the first direct detection of the diffuse intergalactic medium (IGM). The absence of Gunn-Peterson H I 1215 absorption shows that the IGM is hot and/or of very low density, thus He I 584 is not seen. He II 304--the most promising line--should be observable from three sources: the diffuse IGM, the discrete Lyman-Alpha clouds, and the much rarer metal line absorption systems. The Gunn-Peterson continuum optical depth is not well constrained by models (range 0.3-3000). The mere detection of this one QSO below 304A would rule out many models, limiting the IGM density, temperature, and ionization mechanisms. The total absence of flux from several targets would rule out other models. The second QSO is the second brightest object known to have flux near 300A. Its redshift is too low to show HeII 304, but it is the only QSO which we know which is bright enough to check the exciting claim by Reimers etal that absorption systems show enhanced O/C abundances.

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