Exploratory Chandra Observations of the Highest-Redshift Quasars

C. Vignali, W. N. Brandt, S. Kaspi, D. P. Schneider (Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802), X. Fan (Institute for Advanced Study, Olden Lane, Princeton, NJ 08540-0631), J. E. Gunn, Michael A. Strauss (Princeton University Observatory, Peyton Hall, Princeton, NJ 08544-1001)

Abstract

We report exploratory Chandra observations of 10 high-redshift (z=4.06-5.27), optically selected quasars. Seven of these quasars are detected, increasing the number of z>4 X-ray detected quasars by 50%. Our detections include four of the five highest-redshift X-ray detected quasars to date, among them SDSSp J021043.17-001818.4, the highest-redshift (z=4.77) radio-loud quasar detected in the X-ray band. The three undetected objects are the Broad Absorption Line quasar SDSSp J112956.10-014212.4, the weak emission-line quasar SDSSp J153259.96-003944.1, and the quasar PSS 1435+3057. A comparison of the quasars' spectral energy distributions (by means of the optical-to-X-ray spectral index, $\alpha_{\rm ox}$) with those of lower-redshift samples indicates that the Chandra quasars are X-ray fainter by a factor $\approx2$. X-ray faintness could be associated with the presence of large amounts of gas in the primeval galaxies harboring these high-redshift quasars. This suggested scenario would be consistent with recent studies conducted on z>4 quasars in other bands. Using the current Chandra data, predictions for the next generation of X-ray observatories, Constellation-X and XEUS, are also provided.

CATEGORY: ACTIVE GALAXIES AND QUASARS