Two For One

Anaïs Martin presenting at AAS 243 in New Orleans.

Quasars are the hearts of active galaxies. They are powered by supermassive black holes, but are so distant 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 greatest redshift, are among the earliest galaxies, so studying these quasars can tell us a great deal about how galaxies formed and evolved.

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

J1253+1046 as seen by ALMA.

Her first goal was to determine whether the two sources were from the same region of space. This was done by looking at their redshifts. If J1253+1046 is two quasars that just happen to line up when viewed from Earth, then their redshifts would be different because one would be more distant than the other. Anaïs found their redshifts agreed, which means either J1253+1046 is a binary quasar of merging galaxies, or it is a single quasar that has been gravitationally lensed to appear as 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 process of merging, which would be a rare sight indeed. On the other hand, the spectra of the two sources are remarkably similar, which suggests they are the same quasar. One that has been gravitationally lensed by a closer galaxy to appear as two sources. However, one source is distinctly dimmer than the other, which isn’t what we would expect to see in a lensed quasar.

The solution, of course, is to gather more data, which 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 are merging, or could explain why one source of the lensed quasar is dimmer than the other.