The radio emission in radio-quiet quasars: the VLBA perspective

Sina Chen, Ari Laor, Ehud Behar, Ranieri D. Baldi, Joseph D. Gelfand

Research output: Contribution to journalArticlepeer-review


The origin of the radio emission in radio-quiet quasars (RQQ) is not established yet. We present new VLBA observations at 1.6 and 4.9 GHz of 10 RQQ (9 detected), which together with published earlier observations of 8 RQQ (5 detected), forms a representative sample of 18 RQQ drawn from the Palomar-Green sample of low z (< 0.5) AGN. The spectral slope of the integrated emission extends from very steep (α < -1.98) to strongly inverted (α = +2.18), and the slopes of 9 of the 14 objects are flat (α > -0.5). Most objects have an unresolved flat-spectrum core, which coincides with the optical Gaia position. The extended emission is generally steep-spectrum, has a low brightness temperature (< 107 K), and is displaced from the optical core (the Gaia position) by ∼5-100 pc. The VLBA core flux is tightly correlated with the X-ray flux, and follows a radio to X-ray luminosity relation of log LR/LX ≃-6, for all objects with a black hole mass log MBH/M⊙ < 8.5. The flatness of the core emission implies a compact source size (≲ 0.1 pc), which likely originates from the accretion disc corona. The mas-scale extended emission is optically thin and of clumpy structure, and is likely produced by an outflow from the center. Radio observations at higher frequencies can further test the accretion disc coronal emission interpretation for the core emission in RQQ.

Original languageEnglish (US)
Pages (from-to)164-182
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - Oct 1 2023


  • galaxies: active
  • galaxies: nuclei
  • quasars: general
  • radio continuum: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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