Monday, June 8, 2015

Astronomers Reveal Most Detailed View Ever of Star Formation in the Distant Universe

The left panel shows the foreground lensing galaxy (observed with Hubble), and the gravitationally lensed galaxy SDP.81, which forms an almost perfect Einstein Ring, is hardly visible.  The middle image shows the sharp ALMA image of the Einstein ring, with the foreground lensing galaxy being invisible to ALMA. The resulting reconstructed image of the distant galaxy (right) using sophisticated models of the magnifying gravitational lens, reveal fine structures within the ring that have never been seen before: Several dust clouds within the galaxy, which are thought to be giant cold molecular clouds, the birthplaces of stars and planets.  Credit: ALMA (NRAO/ESO/NAOJ)/Y. Tamura (The University of Tokyo)/Mark Swinbank (Durham University)

ALMA’s Long Baseline Campaign has produced a spectacular image of a distant galaxy being gravitationally lensed. The image shows a magnified view of the galaxy’s star-forming regions, the likes of which have never been seen before at this level of detail in a galaxy so remote. The new observations are far sharper than those made using the NASA/ESA Hubble Space Telescope, and reveal star-forming clumps in the galaxy equivalent to giant versions of the Orion Nebula in the Milky Way.

ALMA’s Long Baseline Campaign has produced some amazing observations, and gathered unprecedentedly detailed information about the inhabitants of the near and distant Universe. Observations made at the end of 2014 as part of the campaign targeted a distant galaxy called HATLAS J090311.6+003906, otherwise known as SDP.81. This light from this galaxy is a victim of a cosmic effect known as gravitational lensing. A large galaxy sitting between SDP.81 and ALMA is acting as a lens, warping and magnifying the view of a more distant galaxy and creating a near-perfect example of a phenomenon known as an Einstein Ring.

At least seven groups of scientists have independently analysed the ALMA data on SDP.81. This flurry of research papers has revealed unprecedented information about the galaxy, including details about its structure, contents, motion, and other physical characteristics.

ALMA acts as an interferometer. Simply speaking, the array’s multiple antennas work in perfect synchrony to collect light as an enormous virtual telescope. As a result, these new images of SDP.81 have a resolution up to six times higher than those taken in the infrared with the NASA/ESA Hubble Space Telescope.

The astronomers’ sophisticated models reveal fine, never-before-seen structure within SDP.81, in the form of dusty clouds thought to be giant repositories of cold molecular gas — the birthplaces of stars and planets. These models were able to correct for the distortion produced by the magnifying gravitational lens.

As a result, the ALMA observations are so sharp that researchers can see clumps of star formation in the galaxy down to a size of about 200 light-years, equivalent to observing giant versions of the Orion Nebula producing thousands of times more new stars at the far side of the Universe. This is the first time this phenomenon has been seen at such an enormous distance.

“The reconstructed ALMA image of the galaxy is spectacular,” says Rob Ivison, co-author of two of the papers and ESO’s Director for Science. “ALMA’s huge collecting area, the large separation of its antennas, and the stable atmosphere above the Atacama desert all lead to exquisite detail in both images and spectra. That means that we get very sensitive observations, as well as information about how the different parts of the galaxy are moving. We can study galaxies at the other end of the Universe as they merge and create huge numbers of stars. This is the kind of stuff that gets me up in the morning!”

Using the spectral information gathered by ALMA, astronomers also measured how the distant galaxy rotates, and estimated its mass. The data showed that the gas in this galaxy is unstable; clumps of it are collapsing inwards, and will likely turn into new giant star-forming regions in the future.

"ALMA was designed to be the most powerful telescope of its kind, but by harnessing the magnifying power of this gravitational lens we were able to study a distant and mysterious object in detail that would have been impossible otherwise," says Todd Hunter, an astronomer at the National Radio Astronomy Observatory and co-author on one of the papers. "This one dataset has spawned an entire series of highly intriguing research, confirming that ALMA offers the astronomical community new avenues to probe the distant Universe." 

Notably, the modeling of the lensing effect also indicates the existence of a supermassive black hole at the centre of the foreground galaxy lens. The central part of SDP.81 is too faint to be detected, leading to the conclusion that the foreground galaxy holds a supermassive black hole with more than 200–300 million times the mass of the Sun.

The number of papers published using this single ALMA dataset demonstrates the excitement generated by the potential of the array’s high resolution and light-gathering power. It also shows how ALMA will enable astronomers to make more discoveries in the years to come, also uncovering yet more questions about the nature of distant galaxies.

Credit: ESOnrao.edu

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