NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Absorption in X-ray spectra of high-redshift quasarsWe present evidence that X-ray absorption is common in high-redshift quasars. We have studied six high-redshift (z approximately 3) quasars with the ROSAT Position Sensitive Proportional Counter (PSPC) of which four are in directions of low Galactic N(sub H). Three out of these four show excess absorption, while only three in approximately 50 z approximately less than 0.4 quasars do, indicating that such absorption must be common, but not ubiquitous, at high redshifts, and that the absorbers must lie at z greater than 0.4. The six quasars were: S5 0014+81, Q0420-388, PKS 0438-436, S4 0636+680. PKS 2000-330, PKS 2126-158, which have redshifts between 2.85 and 3.78. PKS 0438-436 and PKS 2126-158 show evidence for absorption above the local Galactic value at better than 99.999% confidence level. If the absorber is at the redshift of the quasar, then values of N(sub H) = (0.86(+0.49, -0.28)) x 10(exp 22) atoms/sq cm for PKS 0438-436, and N(sub H) = (1.45(+1.20, -0.64)) x 10(exp 22) atoms/ sq cm for PKS 2126-158, are implied, assuming solar abundances. The spectrum of S4 0636+680 also suggests the presence of a similarly large absorption column density at the 98% confidence level. This absorption reverses the trend for the most luminous active galactic nuclei (AGN) to have the least X-ray absorption, so a new mechanism is likely to be responsible. Intervening absorption due to damped Lyman(alpha) systems is a plausible cause. We also suggest, as an intrinsic model, that intracluster material, e.g., a cooling flow, around the quasar could account for both the X-ray spectrum and other properties of these quasars. All the quasars are radio-loud and three are gigahertz peaked (two of the three showing absorption). No excess absorption above the Galactic value is seen toward Q0420-388. This quasar has two damped Lyman(alpha) systems at z = 3.08. The limit on the X-ray column density implies a low ionization fraction, N(H I)/N(H) approximately greater than 4 x 10(exp -3) (3 (sigma)), for solar abundances, for these systems, and can set a weak limit on the size of the absorber. In the emitted frame these PSPC spectra cover the band approximately 0.5-10 keV, which has been well observed for low-redshift quasars and AGN. Comparison of high and low-redshift spectra in this emitted band shows no change of mean spectral index greater than Delta alpha(sub E) greater than 0.3 (99% confidence) with either redshift or luminosity, for radio-loud quasars.
Document ID
19950037251
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Elvis, Martin
(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA United States)
Fiore, Fabrizio
(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA United States)
Wilkes, Belinda
(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA United States)
Mcdowell, Jonathan
(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA United States)
Bechtold, Jill
(Univ. of Arizona, Tucson, AZ United States)
Date Acquired
August 16, 2013
Publication Date
February 10, 1994
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 422
Issue: 1
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A68850
Funding Number(s)
CONTRACT_GRANT: NAS8-39073
CONTRACT_GRANT: NAG5-1872
CONTRACT_GRANT: NAG5-1536
CONTRACT_GRANT: NAS5-30934
CONTRACT_GRANT: NAS5-30751
CONTRACT_GRANT: NAGW-2201
Distribution Limits
Public
Copyright
Other

Available Downloads

There are no available downloads for this record.
No Preview Available