Top: Two-dimensional GMOS spectrum of the strong emission line observed in the radio galaxy TGSS J1530+1049. The size of the emission region is a bit less than one arcsec. Bottom: One-dimensional profile of the observed emission line. The asymmetry indicates that the line is Lyman-α at redshift of z = 5.72, making TGSS J1530+1049 the most distant radio galaxy known to date.
Using the Gemini North telescope in Hawai`i, an international team of
astronomers from Brazil, Italy, the Netherlands, and the UK has
discovered the most distant radio galaxy to date, at 12.5 billion light
years, when the Universe was just 7% of its current age.
The team used spectroscopic data from the Gemini Multi-Object
Spectrograph (GMOS-N) to measure a redshift of z = 5.72 for the radio
galaxy identified as TGSS J1530+1049. This is the largest redshift of
any known radio galaxy. The redshift of a galaxy tells astronomers its
distance because galaxies at greater distances move away from us at
higher speeds, and this motion causes the galaxy's light to shift
farther into the red. Because light has a finite speed and takes time to
reach us, more distant galaxies are also seen at earlier times in the
history of the Universe.
The study was led by graduate students Aayush Saxena (Leiden
Observatory, Netherlands) and Murilo Marinello (Observatório Nacional,
Brazil), and the observations were obtained through Brazil's
participation in Gemini. "In the Gemini spectrum of TGSS J1530+1049, we
found a single emission line of hydrogen, known as the Lyman alpha. The
observed shift of this line allowed us to estimate the galaxy's
distance," explains Marinello.
The relatively small size of the radio emission region in TGSS
J1530+1049 indicates that it is quite young, as expected at such early
times. Thus, the galaxy is still in the process of assembling. The radio
emission in this kind of galaxy is powered by a supermassive black hole
that is sucking in material from the surrounding environment. This
discovery of the most distant radio galaxy confirms that black holes can
grow to enormous masses very quickly in the early Universe.
The measured redshift of TGSS J1530+1049 places it near the end of
the Epoch of Reionization, when the majority of the neutral hydrogen in
the Universe was ionized by high-energy photons from young stars and
other sources of radiation. "The Epoch of Reionization is very important
in cosmology, but it is still not well understood," said Roderik
Overzier, also of Brazil's Observatorio Nacional, and the Principal
Investigator of the Gemini program. "Distant radio galaxies can be used
as tools to find out more about this period."
The research has been published by Monthly Notices of the Royal Astronomical Society. A preprint of the paper is available at astro-ph.
Source: Gemini Observatory
