A BL Lacertae Object at a Cosmic Age of 800 Myr
Abstract
We report the discovery of the BL Lacertae object FIRST J233153.20+112952.11 at redshift >6 using near-infrared spectroscopy and broadband observations in the infrared, submillimeter, and radio wavelengths. The detection of the continuum break at ~0.92 μm in the near-infrared spectrum of FIRST J233153.20+112952.11 provides an approximate redshift of 6.57, corresponding to an age of the universe of ~800 Myr. The rest-frame UV/optical spectrum of FIRST J233153.20+112952.11 shows no emission lines detected with equivalent width >1.5 Å. The nondetection of the C IV λ1549 broad emission line constrains the luminosity of the accretion disk to be ≲1045 erg s-1, which corresponds to the radiatively inefficient accretion regime of BL Lacertae objects. The spectral index of the rest-frame UV/optical continuum, α ν,opt = 1.43 ± 0.23, is consistent with the expected spectral index of the synchrotron emission spectrum of the relativistic jet. The flat radio continuum (α ν,r ≈ 0) in a rest-frame frequency interval of 7-23 GHz is similar to that of the typical BL Lacertae objects and also consistent with originating from the synchrotron jet emission. The rest-frame UV/optical and radio fluxes of FIRST J233153.20+112952.11 show significant (15%-40%) variations. The shortest recorded rest-frame timescale of these variations is ~8 days. Assuming the local scaling relation between the radio luminosity and black hole mass, the 5 GHz radio luminosity of FIRST J233153.20+112952.11, 1.6 × 1033 erg s-1 Hz-1, suggests a billion solar mass central supermassive black hole.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 2022
- DOI:
- 10.3847/2041-8213/ac61e0
- Bibcode:
- 2022ApJ...929L...7K
- Keywords:
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- Galaxies;
- Galaxy evolution;
- High-redshift galaxies;
- Active galaxies;
- Active galactic nuclei;
- Blazars;
- BL Lacertae objects;
- Radio jets;
- Supermassive black holes;
- Observational astronomy;
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