http://arxiv.org/abs/2006.13762
We present Giant Metrewave Radio Telescope (GMRT) 323 MHz radio continuum observations towards thirteen radio-loud quasars at $z>5$, sampling the low frequency synchrotron emission from these objects. Among the twelve targets observed successfully, ten are detected above $4\sigma$ significance, while two are undetected. All of the detected sources appear as point sources. Combined with previous radio continuum detections from the literature, nine quasars have power-law spectral energy distributions throughout the radio range; for some the flux density drops with increasing frequency while it increases for others. Two of these sources appear to have spectral turnover. For the power-law-like sources, the power-law indices have a positive range between 0.18 and 0.67, and a negative values between $-0.90$ and $-0.27$. For the turnover sources, the radio peaks around $\sim1$ and $\sim10$ GHz in the rest frame, the optical-thin indices are $-0.58$ and $-0.90$, and the optical-thick indices are 0.50 and 1.20. A magnetic field and spectral age analysis of SDSS J114657.59+403708.6 at $z=5.01$ may indicate that the turnover is not caused by synchrotron self-absorption, but rather by free-free absorption by the high density medium in the nuclear region. Alternatively, the apparent turnover may be an artifact of source variability. Finally, we calculate the radio loudness $R_{2500\rm\, \AA}$ for our sample which spans a very wide range from 12$^{+13}{-13}$ to 4982$^{+279}{-254}$.
Y. Shao, J. Wagg, R. Wang, et. al.
Thu, 25 Jun 20
51/78
Comments: 13 pages; Accepted by A&A
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