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Register a new userResolving the Radio Emission from the Quasar P172+18 at $z = 6.82$
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We present high angular resolution imaging of the quasar PSO J172.3556+18.7734 at $z=6.82$ with the Very Long Baseline Array (VLBA). This source currently holds the record of being the highest redshift radio-loud quasar. These observations reveal a dominant radio source with a flux density of $398.4 pm 61.4~mu$Jy at 1.53 GHz, a deconvolved size of $9.9 times 3.5$ mas ($52.5 times 18.6$ pc), and an intrinsic brightness temperature of ($4.7 pm 0.7) times 10^7$ K. A weak unresolved radio extension from the main source is also detected at $sim~3.1sigma$ level. The total flux density recovered with the VLBA at 1.53 GHz is consistent with that measured with the Very Large Array (VLA) at a similar frequency. The quasar is not detected at 4.67 GHz with the VLBA, suggesting a steep spectral index with a limit of $alpha^{1.53}_{4.67} < -$1.55. The quasar is also not detected with the VLBA at 7.67 GHz. The overall characteristics of the quasar suggest that it is a very young radio source similar to lower redshift Gigahertz Peaked Spectrum radio sources, with an estimated kinematic age of $sim~10^3$ years. The VLA observations of this quasar revealed a second radio source in the field $23rlap{.}{}1$ away. This radio source, which does not have an optical or IR counterpart, is not detected with the VLBA at any of the observed frequencies. Its non-detection at the lowest observed VLBA frequency suggests that it is resolved out, implying a size larger than ~$0rlap{.}{}17$. It is thus likely situated at lower redshift than the quasar.
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We present high angular resolution imaging ($23.9 times 11.3$ mas, $138.6 times 65.5$ pc) of the radio-loud quasar PSO~J352.4034$-$15.3373 at $z=5.84$ with the Very Long Baseline Array (VLBA) at 1.54 GHz. This quasar has the highest radio-to-optical flux density ratio at such a redshift, making it the radio-loudest source known to date at $z sim 6$. The VLBA observations presented here resolve this quasar into multiple components with an overall linear extent of 1.62 kpc ($0rlap{.}{}28$) and with a total flux density of $6.57 pm 0.38$ mJy, which is about half of the emission measured at a much lower angular resolution. The morphology of the source is comparable with either a radio core with a one-sided jet, or a compact or a medium-size Symmetric Object (CSO/MSO). If the source is a CSO/MSO, and assuming an advance speed of $0.2c$, then the estimated kinematic age is $sim 10^4$ yr.
Radio sources at the highest redshifts can provide unique information on the first massive galaxies and black holes, the densest primordial environments, and the epoch of reionization. The number of astronomical objects identified at z>6 has increased dramatically over the last few years, but previously only three radio-loud (R2500>10) sources had been reported at z>6, with the most distant being a quasar at z=6.18. Here we present the discovery and characterization of P172+18, a radio-loud quasar at z=6.823. This source has an MgII-based black hole mass of ~3x10^8 Msun and is one of the fastest accreting quasars, consistent with super-Eddington accretion. The ionized region around the quasar is among the largest measured at these redshifts, implying an active phase longer than the average lifetime of the z>6 quasar population. From archival data, there is evidence that its 1.4 GHz emission has decreased by a factor of two over the last two decades. The quasars radio spectrum between 1.4 and 3.0 GHz is steep (alpha=-1.31) and has a radio-loudness parameter R2500~90. A second steep radio source (alpha=-0.83) of comparable brightness to the quasar is only 23.1 away (~120 kpc at z=6.82; projection probability <2%), but shows no optical or near-infrared counterpart. Further follow-up is required to establish whether these two sources are physically associated.
We have used the SINFONI near-infrared integral field unit on the VLT to resolve the optical emission line structure of one of the brightest (L~1e44 erg/s) and nearest (z=2.38) of all Lya blobs (LABs). The target, known in the literature as object B1 (Francis et al. 1996), lies at a redshift where the main optical emission lines are accessible in the observed near-infrared. We detect luminous [OIII]4959,5007A and Ha emission with a spatial extent of at least 32x40 kpc (4x5). The dominant optical emission line component shows relatively broad lines (600-800 km/s, FWHM) and line ratios consistent with AGN-photoionization. The new evidence for AGN photoionization, combined with previously detected CIV and luminous, warm infrared emission, suggest that B1 is the site of a hidden quasar. This is confirmed by the fact that [OII] is relatively weak compared to [OIII] (extinction-corrected [OIII]/[OII] of about 3.8), which is indicative of a high, Seyfert-like ionization parameter. From the [OIII] luminosity we infer a bolometric AGN luminosity of ~3e46 erg/s, and further conclude that the obscured AGN may be Compton-thick given existing X-ray limits. The large line widths observed are consistent with clouds moving within the narrow line region of a luminous QSO. The AGN scenario is capable of producing sufficient ionizing photons to power the Lya, even in the presence of dust. By performing a census of similar objects in the literature, we find that virtually all luminous LABs harbor obscured quasars. Based on simple duty-cycle arguments, we conclude that AGN are the main drivers of the Lya in LABs rather than the gravitational heating and subsequent cooling suggested by cold stream models. We also conclude that the empirical relation between LABs and overdense environments at high redshift must be due to a more fundamental correlation between AGN (or massive galaxies) and environment.
The interactions between radio jets and the interstellar medium play a defining role for the co-evolution of central supermassive black holes and their host galaxies, but observational constraints on these feedback processes are still very limited at redshifts $z > 2$. We investigate the radio-loud quasar PSO J352.4034-15.3373 at $z sim 6$ at the edge of the Epoch of Reionization. This quasar is among the most powerful radio emitters and the first one with direct evidence of extended radio jets ($sim$1.6 kpc) at these high redshifts. We analyze NOEMA and ALMA millimeter data targeting the CO (6-5) and [CII] far-infrared emission lines, respectively, and the underlying continuum. The broad $440pm 80$ km s$^{-1}$ and marginally resolved [CII] emission line yields a systemic redshift of $z!=!5.832 pm 0.001$. Additionally, we report a strong 215 MHz radio continuum detection, $88pm 7$ mJy, using the GMRT. This measurement significantly improves the constraints at the low-frequency end of the spectral energy distribution of this quasar. In contrast to what is typically observed in high-redshift radio-quiet quasars, we show that cold dust emission alone cannot reproduce the millimeter continuum measurements. This is evidence that the strong synchrotron emission from the quasar contributes substantially to the emission even at millimeter (far-infrared in the rest-frame) wavelengths. This quasar is an ideal system to probe the effects of radio jets during the formation of a massive galaxy within the first Gyr of the Universe.
We carry out a series of deep Karl G. Jansky Very Large Array (VLA) S-band observations of a sample of 21 quasars at $zsim6$. The new observations expand the searches of radio continuum emission to the optically faint quasar population at the highest redshift with rest-frame $4400 rm AA$ luminosities down to $3 times10^{11} L_{odot}$. 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 $87.0 pm 6.3 mu rm Jy$ and $55.4 pm 6.7 mu rm Jy$, respectively. Their radio replaced{loudness}{loudnesses} are estimated to be $54.9 pm 4.7$ and $16.5 pm 3.2$, 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 deleted{and} possible selection effects. The final derived RLF is $9.4 pm 5.7%$ for the optically selected quasars at $zsim6$. 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 replaced{result}{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.
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