A Chandra snapshot survey of representative high-redshift radio-loud quasars from the Parkes-MIT-NRAO sample.
LOPEZ L.A., BRANDT W.N., VIGNALI C., SCHNEIDER D.P., CHARTAS G. and GARMIRE G.P.
Abstract (from CDS):
We present the results of Chandra ACIS-S snapshot observations of six radio-loud quasars (RLQs) at z~3.5-4.7. These observations sample luminous RLQs with moderate to high radio loudness (R~200-9600) and aim to connect the X-ray properties of radio-quiet quasars (R<10) and highly radio-loud blazars (R>1000) at high redshift. This work extends a study by Bassett and coworkers that used similar methods to examine z>4 RLQs with moderate radio loudness (R~40-400). All of our targets are clearly detected. A search for extended X-ray emission associated with kiloparsec-scale radio jets revealed only limited evidence for X-ray extension in our sample: three sources showed no evidence of X-ray extension, and the other three had 3%-30% of their total X-ray fluxes extended >1" away from their X-ray cores. In addition, we do not observe any systematic flattening of the optical-to-X-ray spectral index (αox) compared to low-redshift quasars. These results suggest that kiloparsec-scale X-ray jet emission is not dominated by inverse Compton scattering of cosmic microwave background seed photons off jet electrons. We measured X-ray continuum shapes and performed individual and joint spectral fits of our data combined with eight archival RLQs. A single power-law model acceptably fitted the data, with best-fit photon indices of 1.72+0.11–0.12 for moderate-R sources and 1.47+0.13–0.12for high-R sources. We added an intrinsic absorption component to our model, and neither the moderate-R nor the high-R fits set a lower bound on NH. The upper limits were NH<3.0x1022/cm2 and NH<2.8x1022/cm2, respectively. Our spectral results suggest that intrinsic absorption does not strongly depend on radio loudness, and high-R sources have flatter power laws than moderate-R sources. Overall, our high-redshift RLQs have basic X-ray properties consistent with similar RLQs in the local universe.
Galaxies: Active - Galaxies: High-Redshift - Galaxies: Jets - Galaxies: Nuclei - Galaxies: Quasars: General