detect. Moreover, powerful radio jets, and
the black holes that power them, have not
had sufficient time to grow to large sizes
at such early times. Now, an international
team of astronomers from Brazil, Italy, the
Netherlands, and the United Kingdom has
discovered the most distant radio galaxy to
date, observed just one billion light years
after the Big Bang, when the Universe was
roughly 7% of its current age.
The team used spectroscopic data from
GMOS-North to measure a redshift of
z = 5.72, based on the Lyman-α line, for the
radio galaxy identified as TGSS J1530 + 1049.
This is the largest redshift of any known ra-
dio galaxy. The object was selected as a
high-redshift radio galaxy candidate based
on its very steep spectral index at a frequen-
cy of 150 megahertz and its compact mor-
phology in radio imaging by the Very Large
Array at 1.4 gigahertz. Searches for a coun-
terpart at the location of the radio source in
publicly available optical and infrared sky
surveys revealed nothing. Consequently,
the source was targeted, blindly, for deep
spectroscopy at Gemini.
The measured redshift of TGSS J1530 + 1049
places this galaxy near the end of the Epoch
of Reionization, when the majority of the
neutral hydrogen in the Universe was ion-
ized by high-energy photons from young
stars and perhaps other sources of radiation.
The question of whether or not active galac-
tic nuclei, including quasars and radio galax-
ies, may have contributed to the reionization
remains controversial. “The Epoch of Reion-
ization is very important in cosmology, but
it is still not well understood,” said Roderik
Overzier, also of Brazil’s Observatório Na-
cional, and the Principal Investigator of the
Gemini program. “Distant radio galaxies can
be used as tools to find out more about this
The research has been published in Monthly
Notic es of the Royal Astronomical Society.
John Blakeslee is the Chief Scientist at Gemini Ob-
servatory and located at Gemini South in Chile.
He can be reached at: [email protected]
The study was led by graduate students
Aayush Saxena (Leiden Observatory, the
Netherlands) and Murilo Marinello (Ob-
servatório Nacional, Brazil), and the ob-
servations were obtained through Brazil’s
participation in Gemini. 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. Because the radio emission
is believed to be powered by a supermas-
sive black hole, this discovery indicates
that black holes can grow to enormous
masses very quickly in the early Universe,
since the black hole must have been in
place long enough for the jet to grow to
its observed size.