Relativistic outflows in two quasars in the Chandra Deep Field South.
ZHENG Z.Y. and WANG J.X.
Abstract (from CDS):
In this paper we provide new 1 Ms Chandra ACIS spectra of two quasars in the Chandra Deep Field South (CDF-S) which had strong and extremely blueshifted X-ray emission/absorption line features in previous 1 Ms spectra, with outflowing bulk velocity v∼0.65-0.84c. In the new 1 Ms spectra, the relativistic blueshifted line feature is solidly confirmed in CXO CDFS J033225.3-274219 (CDFS 46, z=1.617), and marginally visible in CXO CDFS J033260.0-274748 (CDFS 11, z=2.579), probably due to the increased Chandra ACIS background in the new 1 Ms exposure. The new data rule out the possibility (although very tiny already based on the old 1Ms data) that the two sources were selected to be unusual due to noise spikes in the spectra. The only likely interpretation is extremely blueshifted iron absorption/emission lines or an absorption edge due to relativistic outflow. We find that the rest-frame emission line center in CDFS 46 marginally decreased from 16.2 to 15.2 keV after 7 years. The line shift could be due to either a decreasing outflowing velocity or a lower ionization level. Including the two quasars reported in this paper, we collect a total of 7 quasars from the literature showing blueshifted emission or absorption line features with v≥0.4c in X-ray spectra, and discuss their connection to jet and/or BAL (broad absorption line) outflows.