This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study reveals a dust-reddened quasar from a time when the universe was less than a billion years old. Located at a redshift of 6.5488, the object J1440+0019 contains a rapidly accreting supermassive black hole with a mass of about 1.1 billion suns.
The paper was posted to the arXiv preprint server on Oct. 9. Cosmic reionization is estimated to have happened roughly between 600 million and a billion years (redshifts 6 to 8) after the Big Bang. This epoch is when ionizing UV radiation from early stars and galaxies converted the universe's neutral hydrogen gas into the ionized state seen today.
Studying quasars and galaxies from this era can put a limit on the redshift at which it occurred. Most quasars from this period are identified by their bright rest-frame ultraviolet light. This method may fail for quasars with even modest dust reddening—their UV emission may be heavily blocked by the surrounding dust envelope.
Previous studies suggest that a large fraction of early active galactic nuclei (AGN) are obscured. Only a handful of reddened quasars are known at redshifts around and beyond 6, and they were found by different methods. In this study, researchers led by Daming Yang of the Leiden Observatory present the details of a quasar at a redshift of 6.55, previously discovered in the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) survey.
The team combined NIRSpec spectroscopy of the core from the James Webb Space Telescope (JWST) with observations from the Atacama Large Millimeter/submillimeter Array (ALMA) of the host galaxy's cold gas and dust. The spectrum of J1440+0019 revealed a shape that matches that of reddening by dust. It revealed prominent emission lines, and together with prominent obscuration, it indicates the presence of a quasar that is moderately hidden by dust along the line of sight.
"This combination identifies J1440+0019 as a red type-1 quasar: the nucleus is viewed directly, but through moderate dust extinction along the sightline," the team writes in the paper. They found some features that are blueshifted—indicative of them moving toward us. Three high-ionization absorption systems appear blueshifted relative to the component that is moving away from us.
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