Constraining the Quasar Radio-loud Fraction at z ∼ 6 with Deep Radio Observations

Abstract

We carry out a series of deep Karl G. Jansky Very Large Array (VLA) S-band observations of a sample of 21 quasars at z ∼ 6. The new observations expand the searches of radio continuum emission to the optically faint quasar population at the highest redshift with rest-frame 4400 Å luminosities down to 3 × 10 11 L ⊙ . We report the detections of two new radio-loud quasars: CFHQS J2242+0334 (hereafter J2242+0334) at z = 5.88 and CFHQS J0227−0605 (hereafter J0227−0605) at z = 6.20, detected with 3 GHz flux densities of 87.0 ± 6.3 μ Jy and 55.4 ± 6.7 μ Jy , respectively. Their radio loudnesses are estimated to be 54.9 ± 4.7 and 16.5 ± 3.2, respectively. To better constrain the radio-loud fraction (RLF), we combine the new measurements with the archival VLA L-band data as well as available data from the literature, considering the upper limits for non-detections and possible selection effects. The final derived RLF is 9.4 ± 5.7% for the optically selected quasars at z ∼ 6. We also compare the RLF to that of the quasar samples at low redshift and check the RLF in different quasar luminosity bins. The RLF for the optically faint objects is still poorly constrained due to the limited sample size. Our results show no evidence of significant quasar RLF evolution with redshift. There is also no clear trend of RLF evolution with quasar UV/optical luminosity due to the limited sample size of optically faint objects with deep radio observations.

Jetted radio-quiet quasars at z>5

“…The presence of a relativistic jet is generally associated with strong radio emission, and the radio-loud fraction in a quasar population is commonly used to trace the occurrence of jetted sources. Radio-loud fraction in z ∼ 6 quasars seems consistent with or lower than the same value in the local Universe (Liu et al 2021). However when aligned sources are considered to trace the jetted population, i.e.…”

The radio spectral turnover of radio-loud quasars at $z>5$

“…In summary, we report new results on ten radio-loud quasars at z > 5, which are listed in Table 1 of this work, and among them five have both new VLA and uGMRT observations. Our sample in this work can represent more than 30% of the entire radio-loud quasars at z > 5 identified by now (e.g., Anderson et al 2001;Fan et al 2001;Sharp et al 2001;Romani et al 2004;McGreer et al 2006McGreer et al , 2009Willott et al 2010;Zeimann et al 2011;Yi et al 2014;Bañados et al 2015Bañados et al , 2018Bañados et al , 2021Belladitta et al 2020;Gupta et al 2021;Ighina et al 2021;Khorunzhev et al 2021;Liu et al 2021).…”

The detectability of strong 21 centimetre forest absorbers from the diffuse intergalactic medium in late reionisation models

“…With ∼ 10 radio-loud active galactic nuclei now known at 5.5 < < 6.5 (e.g. Bañados et al 2018b;Liu et al 2021) and the prospect of more radio-loud sources being identified in the next few years, this possibility merits further investigation.…”

“…Approximately ∼ 10 radio-loud active galactic nuclei are now known at 5.5 < < 6.5 (e.g. Bañados et al 2018bBañados et al , 2021Liu et al 2021;Ighina et al 2021), including the = 6.1 blazar PSO J0309+27 with a flux density 147 MHz = 64.2±6.2 mJy (Belladitta et al 2020). The Low Frequency Array (LOFAR) Twometre Sky Survey (LoTSS, Shimwell et al 2017;Kondapally et al 2020), the Giant Metrewave Radio Telescope (GMRT) all sky radio survey at 150 MHz (Intema et al 2017), and the Galactic and Extragalactic All-sky Murchison Widefield Array survey (GLEAM, Wayth et al 2015) are also projected to detect hundreds of bright > 6 radio sources, particularly if coupled with large spectroscopic follow-up programmes such as the William Herschel Telescope Enhanced Area Velocity Explorer (WEAVE)-LOFAR survey (Smith et al 2016).…”