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

Abstract

We present Karl G. Jansky Very Large Array (VLA) 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 $\sim$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 $\sim$1--50 GHz in the rest frame, making these targets gigahertz-peaked-spectrum (GPS) or high-frequency-peaker (HFP) 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 $R_{2500\mathring{\mathrm{A}}}$ for our sample, which ranges from 12${}_{-1}^{+1}$ to 674${}_{-51}^{+61}$.

arXiv commentAccepted for publication in A&A

References in corpus (73)

• emcee: The MCMC Hammer
• Planck 2015 results. XIII. Cosmological parameters
• The SINS survey: SINFONI Integral Field Spectroscopy of z ~ 2 Star-forming Galaxies
• A Survey of z>5.8 Quasars in the Sloan Digital Sky Survey I: Discovery of Three New Quasars and the Spatial Density of Luminous Quasars at z~6
• The GMRT 150 MHz All-sky Radio Survey: First Alternative Data Release TGSS ADR1
• The Canada-France High-z Quasar Survey: nine new quasars and the luminosity function at redshift 6
• 350 Micron Dust Emission from High Redshift Quasars
• The Last of FIRST: The Final Catalog and Source Identifications
• SCUBA-2: iterative map-making with the Sub-Millimetre User Reduction Facility
• SCUBA-2: on-sky calibration using submillimetre standard sources
• LOFAR 150-MHz observations of the Boötes field: Catalogue and Source Counts
• Compact steep-spectrum and peaked-spectrum radio sources
• The Dynamic Evolution of Young Extragalactic Radio Sources
• A complete sample of GHz-Peaked-Spectrum radio sources and its radio properties
• A determination of the Spectra of Galactic components observed by WMAP
• Spectral Energy Distributions of QSOs at z>5: common AGN-heated dust and occasionally strong star-formation
• Constraining the radio-loud fraction of quasars at z>5.5
• The State-of-Play of Anomalous Microwave Emission (AME) Research
• Relativistic jet feedback II: Relationship to gigahertz peak spectrum and compact steep spectrum radio galaxies
• High Frequency Peakers: young radio sources or flaring blazars?
• The Star Formation in Radio Survey: GBT 33 GHz Observations of Nearby Galaxy Nuclei and Extranuclear Star-Forming Regions
• High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data VI. Sloan Digital Sky Survey Spectrograph Observations
• High-resolution VLA Imaging of SDSS Stripe 82 at 1.4 GHz
• Obscuration of the Parsec Scale Jets in the Compact Symmetric Object 1946+708
• Q0906+6930: The Highest-Redshift Blazar
• The first blazar observed at z>6
• The Detection of Anomalous Dust Emission in the Nearby Galaxy NGC 6946
• Broadband Spectral Modeling of the Extreme Gigahertz-Peaked Spectrum Radio Source PKS B0008-421
• Discovery of a z=6.1 Radio-Loud Quasar in the NDWFS
• The discovery of a highly accreting, radio-loud quasar at z=6.82
• Cold and warm molecular gas in the outflow of 4C12.50
• A new sample of faint Gigahertz Peaked Spectrum radio sources
• Sensitive observations at 1.4 and 250 GHz of z > 5 QSOs
• Compact steep-spectrum sources from the S4 sample
• A powerful radio-loud quasar at the end of cosmic reionization
• Molecular Gas in the Powerful Radio Nucleus of the Ultraluminous Infrared Galaxy PKS 1345+12
• A Case Against Spinning PAHs as the Source of the Anomalous Microwave Emission
• Are young radio sources in equipartition?
• The first estimate of radio jet proper motion at z>5
• Into the central 10 pc of the most distant known radio quasar. VLBI imaging observations of J1429+5447 at z=6.21
• Constraining the quasar radio-loud fraction at $z\sim 6$ with deep radio observations
• Parsec-scale properties of the radio brightest jetted AGN at z > 6
• Jets blowing bubbles in the young radio galaxy 4C 31.04
• High-resolution double morphology of the most distant known radio quasar at z=6.12
• The Spectral Variability of the GHz-Peaked Spectrum Radio Source PKS 1718-649 and a Comparison of Absorption Models
• Discovery of a Radio-Selected z ~ 6 Quasar
• First constraints on the AGN X-ray luminosity function at $z\sim 6$ from an eROSITA-detected quasar
• A population of hypercompact HII regions identified from young HII regions
• Radio Detection of VIK J2318$-$3113, the Most Distant Radio-Loud Quasar ($z$=6.44)
• Resolving the Powerful Radio-loud Quasar at z~6
• SDSS J114657.79+403708.6: the third most distant blazar at z=5.0
• High-resolution radio imaging of the most distant radio quasar SDSS J0836+0054
• VLA and VLBA Observations of the Highest Redshift Radio-Loud QSO J1427+3312 at z = 6.12
• Radio structure of the most distant radio-detected quasar at the ten milli- arcsecond scale
• Radio-Selected Quasars in the Sloan Digital Sky Survey
• Correlation between X-ray and radio absorption in compact radio galaxies
• SDSS J013127.34$-$032100.1: A newly discovered radio-loud quasar at $z=5.18$ with extremely high luminosity
• Numerical calculations of spectral turnover and Synchrotron Self Absorption in CSS and GPS radio sources
• VLBI observations of the radio quasar J2228+0110 at z=5.95 and other field sources in multiple-phase-centre mode
• 3C459: A highly asymmetric radio galaxy with a starburst
• High-resolution images of five radio quasars at early cosmological epochs
• Discovery of the most X-ray luminous quasar SRGE J170245.3+130104 at redshift z$\approx 5.5$
• Resolving the Radio Emission from the Quasar P172+18 at $z=6.82$
• Parsec-scale morphology and spectral index distribution in faint high frequency peakers
• A New Detection of Extragalactic Anomalous Microwave Emission in a Compact, Optically-Faint Region of NGC\,4725
• A search for HI 21cm absorption toward the highest redshift radio loud objects
• Constraining the spectral age of very asymmetric CSOs
• First results from the Isaac Newton Telescope Wide Angle Survey: The z>5 quasar survey
• VLBI observation of the newly discovered z=5.18 quasar SDSS J0131-0321
• Gemini-South + FLAMINGOS Demonstration Science: Near-Infrared Spectroscopy of the z=5.77 Quasar SDSS J083643.85+005453.3
• Radio Source Evolution on Galactic Scales
• Observations by GMRT at 323 MHz of radio-loud quasars at $z>5$
• A GMRT 150 MHz Search for Variables and Transients in Stripe 82

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• Radio-loud Quasars above Redshift 4: VLBI Imaging of an Extended Sample
• The 21-cm forest as a simultaneous probe of dark matter and cosmic heating history
• New Radio-Loud QSOs at the end of the Re-ionisation Epoch
• A global view on star formation: The GLOSTAR Galactic plane survey. IX. Radio Source Catalog III: 2<l<28, 36<l<40, 56<l<60 and |b|<1, VLA B-configuration
• Constraining the Radio Properties of the $z$=6.44 QSO VIK J2318$-$3113
• Low-redshift Lyman Continuum Survey: Radio continuum properties of low-$z$ Lyman continuum emitters
• A powerful (and likely young) radio-loud quasar at z=5.3
• Multi-wavelength properties of three new radio-powerful $z\sim 5.6$ quasi-stellar objects discovered from RACS
• The host galaxies of radio-loud quasars at z>5 with ALMA
• Comprehensive view on a $z\sim 6.5$ radio-loud QSO: from the radio to the optical/NIR to the X-ray band
• No strong radio absorption detected in the low-frequency spectra of radio-loud quasars at z > 5.6
• High-$z$ radio Quasars in RACS I: Selection, identification, and multi-wavelength properties
• Monster radio jet (>66 kpc) observed in quasar at z$\sim$5
• Revealing faint compact radio jets at redshifts above 5 with very long baseline interferometry
• Radio and Optical Properties of the blazar PKS 1614+051 at z=3.21
• Milliarcsecond-scale radio structure of the most distant BL Lac object candidate at redshift 6.57
• Milliarcsecond-resolution Radio-imaging Survey of Blazar Candidates at 4 < z < 5.4