Portal de Periódicos da CAPES

Absorption in X-ray spectra of high-redshift quasars

1994; IOP Publishing; Volume: 422; Linguagem: Inglês

10.1086/173703

1538-4357

M. Elvis, F. Fiore, B. J. Wilkes, Jonathan McDowell, Jill Bechtold,

Astronomical Observations and Instrumentation

view Abstract Citations (125) References (90) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Absorption in X-Ray Spectra of High-Redshift Quasars Elvis, Martin ; Fiore, Fabrizio ; Wilkes, Belinda ; McDowell, Jonathan ; Bechtold, Jill Abstract We present evidence that X-ray absorption is common in high-redshift quasars. We have studied six high-redshift (z~3) quasars with the ROSAT PSPC of which four are in directions of low Galactic N_H_. Three out of these four show excess absorption, while only three in ~50 z <~ 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 > 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_H_ = [0.86(+0.49 -0.28)] x 10^22^ atoms cm^-2^ for PKS 0438-436, and N_H_ = [1.45(+1.20, -0.64)] x 10^22^ atoms cm^-2^ 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 Lyα 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 Lyα systems at z = 3.08. The limit on the X-ray column density implies a low ionization fraction, N(H I)/N(H) ~> 4 x 10^-3^(3σ), 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 ~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}α_E_ > 0.3(99% confidence) with either redshift or luminosity, for radio-loud quasars. Publication: The Astrophysical Journal Pub Date: February 1994 DOI: 10.1086/173703 Bibcode: 1994ApJ...422...60E Keywords: Absorption Spectra; Active Galactic Nuclei; Galaxies; Quasars; Red Shift; Spectral Energy Distribution; X Ray Astronomy; X Ray Spectra; Lyman Alpha Radiation; Position Sensing; Proportional Counters; Rosat Mission; Astrophysics; GALAXIES: QUASARS: ABSORPTION LINES; X-RAYS: GALAXIES full text sources ADS | data products NED (6) SIMBAD (5)