Chandra observations of radio-loud quasars at z>4: x-rays from the radio beacons of the early universe.
BASSETT L.C., BRANDT W.N., SCHNEIDER D.P., VIGNALI C., CHARTAS G. and GARMIRE G.P.
Abstract (from CDS):
We present the results of Chandra observations of six radio-loud quasars (RLQs) and one optically bright radio-quiet quasar (RQQ) at z~4.1-4.4. These observations cover a representative sample of RLQs with moderate radio loudness (R~40-400), filling the X-ray observational gap between optically selected RQQs (predominantly R≲2-10) and the five known blazars at z>4 (R~800-27,000), where R=f5GHz/f4400Å(rest frame). We study the relationship between X-ray luminosity and radio loudness for quasars at high redshift and constrain RLQ X-ray continuum emission and absorption. From a joint spectral fit of nine moderate-R RLQs observed by Chandra, we find tentative evidence for absorption above the Galactic NH, with a best-fit neutral intrinsic column density of NH=2.4+2.0–1.8x1022/cm2, consistent with earlier claims of increased absorption toward high-redshift RLQs. We also search for evidence of an enhanced jet-linked component in the X-ray emission due to the increased energy density of the cosmic microwave background at high redshift, but we find neither spatial detections of X-ray jets nor a significant enhancement in the X-ray emission relative to comparable RLQs at low to moderate redshifts. Overall, the z~4-5 RLQs have basic X-ray properties consistent with comparable RLQs in the local universe, suggesting that the accretion/jet mechanisms of these objects are similar as well.
Galaxies: Active - Galaxies: High-Redshift - Galaxies: Jets - Galaxies: Nuclei - Galaxies: Quasars: General