An international team of astronomers used Wide Field Camera 3 aboard NASA’s Hubble Space Telescope to look at the host galaxy of one of the most luminous quasars ever seen.
This Hubble image shows the quasar J1148+5251, one of the most distant and luminous quasars ever seen (NASA / ESA / M. Mechtley / R. Windhorst / Arizona State University)
The quasar J1148+5251 dates back to an early time in the Universe’s history. According to NASA researchers, this distant object was known to contain large amounts of dust from previous sub-millimeter observations. What surprised the astronomers is how completely the dust is shrouding starlight within the host galaxy – none of the starlight seems to be leaking out from around the quasar.
“If you want to hide the stars with dust, you need to make lots of short-lived massive stars earlier on that lose their mass at the end of their lifetime,” explained Dr Rogier Windhorst of Arizona State University, co-author of a paper publishing the results in the Astrophysical Journal Letters (arXiv.org version).
“You need to do this very quickly, so supernovae and other stellar mass-loss channels can fill the environment with dust very quickly,” he said.
“You also have to be forming them throughout the galaxy to spread the dust throughout the galaxy,” said lead author Dr Matt Mechtley of Arizona State University.
The quasar was first identified in the Sloan Digital Sky Survey, follow-up observations at sub-millimeter wavelengths detected significant dust within the galaxy, but did not show how and where dust was distributed, and if or where star-clusters might be visible through the dust.
The astronomers used Hubble to subtract light from the quasar image and look for the glow of surrounding stars. They accomplished this by looking at the glow of a reference star in the sky near the quasar and using it as a template to remove the quasar light from the image. Once the quasar was removed, no significant underlying starlight was detected. The underlying galaxy’s stars could have been easily detected, had they been present and relatively unobscured by dust in at least some locations.
“It is remarkable that Hubble didn’t find any of the underlying galaxy,” Dr Windhorst said. “The underlying galaxy is everywhere much fainter than expected, and therefore must be in a very dusty environment throughout. It’s one of the most rip-roaring forest fires in the Universe. It’s creating so much smoke that you’re not seeing any starlight, anywhere. The forest fire is complete, not a tree is spared.”
“Because we don’t see the stars, we can rule out that the galaxy that hosts this quasar is a normal galaxy,” Dr Mechtley said. “It’s among the dustiest galaxies in the Universe, and the dust is so widely distributed that not even a single clump of stars is peeking through. We’re very close to a plausible detection, in the sense that if we had gone a factor of two deeper we might have detected some light from its young stars, even in such a dusty galaxy.”
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Bibliographic information: M. Mechtley et al. 2012. Near-infrared Imaging of a z = 6.42 Quasar Host Galaxy with the Hubble Space Telescope Wide Field Camera 3. ApJ 756, L38; doi: 10.1088/2041-8205/756/2/L38
