CEA astronomers unravel blending and discover new galaxies with ALMA

Surveys at "submillimetre" wavelengths (typically several hundred microns) reveal a substantial population bright submillimetre sources, which trace dust emission in distant galaxies. Follow-up observations at higher resolution reveal that these submillimetre sources are comprised of a population of highly active distant galaxies, which are forming stars hundreds or thousands of times faster than our own Milky Way. However, there's a problem! About half of the submillimetre sources are composed of more than one of these so-called submillimetre galaxies (SMGs), which is more than expected by chance (implying that the different galaxies may be related), but most galaxy evolution theories predict that the component galaxies are unrelated. Previous observations were unable to distinguish between the two scenarios, so CEA astronomers set up an experiment to do just that.

Using ALMA, the high-resolution (sub)millimetre instrument in Chile, they searched for carbon monoxide (CO) gas emission from pairs of SMGs in the blended systems. In most cases they were only able to detect CO in one of the SMGs, showing that ~65% of the time the multiple component galaxies are NOT physically associated, and are found close together by chance (as predicted by theory). The astronomers also serendipitously discovered new galaxies that contain a lot of CO gas or dust in many of the SMG systems. By combining the findings from their new observations with archival data the researchers were showed that many SMGs have nearby companions, which though typically not close enough to be gravitationally triggering their huge star-formation rates, they may end up in the same galaxy cluster.

Example of one of the targeted fields
The image shows and example the new ALMA data in of one of the targeted fields. The left-hand panel shows the 3 mm emission and the middle panel is the CO emission; in both originally targeted SMGs are highlighted in green, and new, serendipitously-detected CO emitters and dusty galaxies are in cyan and orange, respectively.

Link to the original research paper: https://arxiv.org/abs/1806.05193

Contacts from CEA, Durham:

Julie Wardlow

Ian Smail

Mark Swinbank

Elizabeth Cooke

Bitten Gullberg