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ALMA Pinpoints Early Galaxies at Record Speed




The best map so far of these distant dusty galaxies was made using the ESO-operated Atacama Pathfinder Experiment telescope (APEX). It surveyed a patch of the sky about the size of the full Moon, and detected 126 such galaxies. But, in the APEX images, each burst of star formation appeared as a relatively fuzzy blob, which may be so broad that it covered more than one galaxy in sharper images made at other wavelengths. Without knowing exactly which of the galaxies are forming the stars, astronomers were hampered in their study of star formation in the early Universe.

Pinpointing the correct galaxies requires sharper observations, and sharper observations require a bigger telescope. While APEX has a single 12-metre-diameter dish-shaped antenna, telescopes such as ALMA use multiple APEX-like dishes spread over wide distances. The signals from all the antennas are combined, and the effect is like that of a single, giant telescope as wide as the whole array of antennas.

The team used ALMA to observe the galaxies from the APEX map during ALMA’s first phase of scientific observations, with the telescope still under construction. Using less than a quarter of the final complement of 66 antennas, spread over distances of up to 125 metres, ALMA needed just two minutes per galaxy to pinpoint each one within a tiny region 200 times smaller than the broad APEX blobs, and with three times the sensitivity. ALMA is so much more sensitive than other telescopes of its kind that, in just a few hours, it doubled the total number of such observations ever made.

Not only could the team unambiguously identify which galaxies had regions of active star formation, but in up to half the cases they found that multiple star-forming galaxies had been blended into a single blob in the previous observations. ALMA’s sharp vision enabled them to distinguish the separate galaxies.


The results form the first statistically reliable catalogue of dusty star-forming galaxies in the early Universe, and provide a vital foundation for further investigations of these galaxies’ properties at different wavelengths, without risk of misinterpretation due to the galaxies appearing blended together.

Despite ALMA’s sharp vision and unrivalled sensitivity, telescopes such as APEX still have a role to play. “APEX can cover a wide area of the sky faster than ALMA, and so it’s ideal for discovering these galaxies. Once we know where to look, we can use ALMA to locate them exactly,” concluded Ian Smail (Durham University, United Kingdom), co-author of the new paper.


Source : European Southern Observatory

Published on ASDNews: Apr 17, 2013


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