two for one

Quasars are the hearts of active galaxies. They are powered by supermassive black holes, but they are so distant that they appear almost point-like similar to stars, hence the term quasi-stellar objects. We now know that the most distant quasars, those with the highest redshift, are among the oldest galaxies, so studying these quasars can tell us a lot about how galaxies formed and evolved.

In 2019, observations from the Atacama Large Millimeter/submillimeter Array (ALMA) found that a high-redshift quasar called J1253+1046 appeared not as one source, but as two. Anaïs Martin, an undergraduate student at the University of Washington, wanted to know why.

Their first goal was to determine whether the two sources came from the same region of space. This was done by observing their redshifts. If J1253+1046 are two quasars that line up when viewed from Earth, then their redshifts would be different because one would be more distant than the other. Anaïs found that their redshifts matched, meaning that J1253+1046 is either a merging galaxy binary quasar, or it is a single quasar that has been gravitationally lensed to make it look like two.

Here the data becomes inconclusive. About a third of quasars have a companion, but in the case of J1253+1046, the two sources are incredibly close to each other. So close that they would be an interacting binary seen in the fusion process, which would be really rare. On the other hand, the spectra of the two sources are remarkably similar, suggesting that they are the same quasar. One that has been gravitationally lensed by a closer galaxy to appear as two sources. However, one source is clearly dimmer than the other, which is not what we would expect to see in a lensed quasar.

The solution, of course, is to collect more data, something Anaïs hopes to do in the future. High-resolution images from ALMA and other observatories could reveal dust in the region, which could show flows between the sources if they merge, or could explain why one lens quasar source is fainter than the other.

The charge two for one appeared first on National Radio Astronomy Observatory.