Astronomers have used CSIRO’s Australia Telescope Compact Array (ATCA) and NASA’s Chandra X-ray Observatory to show that a recently-discovered lensed galaxy has one of the highest rates of star formation ever seen in a galaxy.
The distorted galaxy in the simulation (main image) results from a collision and merger between two galaxies. Astronomers think such a merger could be the reason why SPT0346-52 is having such a boom of stellar construction. Once the two galaxies collide, gas near the center of the merged galaxy (shown as the bright region in the center of the simulation) is compressed, producing a burst of new stars. The composite inset shows X-ray data from Chandra (blue), short wavelength infrared data from Hubble (green), infrared light from Spitzer (red) at longer wavelengths, and infrared data from ALMA (magenta) at even longer wavelengths. There is no blue at the center of the image, showing that Chandra did not detect any X-rays that could have signaled the presence of a growing black hole. Image credit: X-ray – NASA / CXC / University of Florida / J. Ma et al; optical – NASA / STScI; infrared – NASA / JPL-Caltech; radio – ESO / NAOJ / NRAO / ALMA; simulation – Simons Foundation / Gordon and Betty Moore Foundation / Flatiron Institute / Caltech / C. Hayward & P. Hopkins.
The galaxy in question, SPT-S J034640-5204.9 (hereafter SPT 0346-52), is 12.7 billion light-years from Earth. This means that astronomers are observing it at a critical stage in the evolution of galaxies, about a billion years after the Big Bang.
SPT 0346-52 was discovered in 2010 by Dr. Joaquin Vieira of the University of Illinois at Urbana-Champaign and his colleagues using NSF’s South Pole Telescope.
The galaxy was then observed with NASA’s Hubble, Spitzer, and ESA’s Herschel space observatories, the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder Experiment, and ESO’s Very Large Telescope.
Dr. Vieira and co-authors were intrigued by SPT0346-52 when the ALMA data revealed extremely bright infrared emission from this galaxy. This suggested that the galaxy is undergoing a tremendous explosion of star birth.
However, another possible explanation for the excess infrared emission was the presence of a rapidly growing supermassive black hole at the galaxy’s center. In this scenario, gas falling towards the black hole would become much hotter and brighter, causing surrounding dust and gas to glow in infrared light.
To distinguish between these two possibilities, the astronomers used Chandra and ATCA telescopes. Neither X-rays nor radio waves were detected, so they were able to rule out a growing black hole generating most of the bright infrared light.
“We now know that this galaxy doesn’t have a gorging black hole, but instead is shining brightly with the light from newborn stars,” said team member Jingzhe Ma, a graduate student at the University of Florida and first author of a study published in the Astrophysical Journal (arXiv.org preprint).
“This gives us information about how galaxies and the stars within them evolve during some of the earliest times in the Universe.”
SPT 0346-52 is part of a population of strong gravitationally-lensed galaxies discovered with NSF’s South Pole Telescope. The light from the galaxy is distorted and magnified by the gravity of an intervening galaxy, producing three elongated images in the ALMA data located near the center of the image. SPT 0346-52 appears about 6 times brighter than it would without gravitational lensing, which enables astronomers to see more details than would otherwise be possible. Image credit: X-ray – NASA / CXC / University of Florida / J. Ma et al; optical – NASA / STScI; infrared – NASA / JPL-Caltech; radio – ESO / NAOJ / NRAO / ALMA.
In SPT0346-52, stars are forming at a rate of 4,500 times the mass of the Sun every year, one of the highest rates seen in a galaxy. This is in contrast to a galaxy like our Milky Way Galaxy that only forms about one solar mass of new stars per year.
“Astronomers call galaxies with lots of star formation starburst galaxies,” said team member Prof. Anthony Gonzalez, also of the University of Florida.
“That term doesn’t seem to do this galaxy justice, so we are calling it a ‘hyper-starburst’ galaxy.”
The high rate of star formation implies that a large reservoir of cool gas in SPT 0346-52 is being converted into stars with unusually high efficiency.
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Jingzhe Ma et al. 2016. SPT0346-52: Negligible AGN Activity in a Compact, Hyper-starburst Galaxy at z = 5.7. ApJ 832, 114; doi: 10.3847/0004-637X/832/2/114
