Milliarcsecond-scale radio structure of the most distant BL Lac object candidate at redshift 6.57

Abstract

The existence of accreting supermassive black holes up to billions of solar masses at early cosmological epochs (in the context of this work, redshifts z>=6) requires very fast growth rates which is challenging to explain. The presence of a relativistic jet can be a direct indication of activity and accretion status in active galactic nuclei (AGN), constraining the radiative properties of these extreme objects. However, known jetted AGN beyond z~6 are still very rare. The radio-emitting AGN J2331+1129 has recently been claimed as a candidate BL Lac object at redshift z=6.57, based on its synchrotron-dominated emission spectrum and the lack of ultraviolet/optical emission lines. It is a promising candidate for the highest-redshift blazar known to date. The aim of the observations described here was to support or refute the blazar classification of this peculiar source. We performed high-resolution radio interferometric imaging observations of J2331+1129 using the Very Long Baseline Array at 1.6 and 4.9 GHz in 2022 Feb. The images revealed a compact but slightly resolved, flat-spectrum core feature at both frequencies, indicating that the total radio emission is produced by a compact jet and originates from within a central 10-pc scale region. While these are consistent with the radio properties of a BL Lac object, the inferred brightness temperatures are at least an order of magnitude lower than expected from a Doppler-boosted radio jet, leaving the high-redshift BL Lac identification still an open question.

5 pages, 1 figure, accepted for publication in Astronomy & Astrophysics as a Letter to the Editor

References in corpus (18)

• Supermassive black hole formation during the assembly of pre-galactic discs
• The third realization of the International Celestial Reference Frame by very long baseline interferometry
• The origins of massive black holes
• Pulsar Parallaxes at 5 GHz with the Very Long Baseline Array
• Intrinsic Brightness Temperatures of AGN Jets
• Precise radio astrometry and new developments for the next generation of instruments
• Exploring the high-redshift PBH-$\Lambda$CDM Universe: early black hole seeding, the first stars and cosmic radiation backgrounds
• Evolving parsec-scale radio structure in the most distant blazar known
• High-resolution double morphology of the most distant known radio quasar at z=6.12
• High-resolution radio imaging of the most distant radio quasar SDSS J0836+0054
• Resolving the Radio Emission from the Quasar P172+18 at $z=6.82$
• The radio spectral turnover of radio-loud quasars at $z>5$
• New Radio-Loud QSOs at the end of the Re-ionisation Epoch
• VLBI observations of VIK J2318-3113, a quasar at z = 6.44
• Milli-arcsecond imaging of the radio emission from the quasar with the most massive black hole at reionization
• A compact symmetric radio source born at one-tenth the current age of the Universe
• Radio Emission from the First Quasars at $z\sim$ 6-15
• The origin of supermassive black holes at cosmic dawn

Cited by in corpus (1)

• High-$z$ radio Quasars in RACS I: Selection, identification, and multi-wavelength properties