GeminiFocus October 2018 - Page 13

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 period.” 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. October 2018 GeminiFocus 11