影响因子：6.2
DOI码：10.1051/0004-6361/202142489
发表刊物：Astronomy & Astrophysics
摘要：We present Karl G. Jansky Very Large Array S- (2-4 GHz), C- (4-8 GHz), and X-band (8-12 GHz) continuum observations toward seven radio-loud quasars at z > 5. This sample has previously been found to exhibit spectral peaks at observed-frame frequencies above ∼1 GHz. We also present upgraded Giant Metrewave Radio Telescope (uGMRT) band-2 (200 MHz), band-3 (400 MHz), and band-4 (650 MHz) radio continuum observations toward eight radio-loud quasars at z > 5, selected from our previous GMRT survey, in order to sample their low-frequency synchrotron emission. Combined with archival radio continuum observations, all ten targets show evidence for spectral turnover. The turnover frequencies are ∼1-50 GHz in the rest frame, making these targets gigahertz-peaked-spectrum or high-frequency-peaker candidates. For the nine well-constrained targets with observations on both sides of the spectral turnover, we fit the entire radio spectrum with absorption models associated with synchrotron self-absorption and free-free absorption (FFA). Our results show that FFA in an external inhomogeneous medium can accurately describe the observed spectra for all nine targets, which may indicate an FFA origin for the radio spectral turnover in our sample. As for the complex spectrum of J114657.79+403708.6 at z = 5.00 with two spectral peaks, it may be caused by multiple components (i.e., core-jet) and FFA by the high-density medium in the nuclear region. However, we cannot rule out the spectral turnover origin of variability. Based on our radio spectral modeling, we calculate the radio loudness R2500 Å for our sample, which ranges from 12−1+1 to 674−51+61.
合写作者：Jeff Wagg, Ran Wang, Emmanuel Momjian, Chris L. Carilli, Fabian Walter, Dominik A. Riechers, Huib T. Intema, Axel Weiss, Andreas Brunthaler and Karl M. Menten
第一作者：Yali Shao
卷号：659
页面范围：A159
是否译文：否
发表时间：2022-03-22
收录刊物：SCI
发布期刊链接：https://www.aanda.org/articles/aa/full_html/2022/03/aa42489-21/aa42489-21.html