Washington: Astronomers were left surprised after detailed studies showed that one of their subjects was not a single galaxy, but rather two, nearly perfectly superimposed on the sky to masquerade as one.
As part of a study of 35 galaxies, the astronomers observed one called UGC 10288, a spiral galaxy more than 100 million light-years distant that appears edge-on as seen from Earth.
Their multiple VLA observations in 2011 and 2012 produced the best radio-telescope images of that galaxy ever made. The detailed images surprisingly revealed a more-distant galaxy, with strong radio emission, almost directly behind UGC 10288. In previous images, the two galaxies had been blended together.
The background galaxy is nearly 7 billion light-years from Earth.
Judith Irwin, of Queen`s University in Ontario, Canada, said that it changed their understanding of the characteristics of UGC 10288, but also gave us an unexpected new tool for learning more about that galaxy.
The first insight gleaned from the improved images was that UGC 10288 is not forming stars as rapidly as the astronomers first thought. This is because much of the radio emission in the previous, blended images came from the background
The new images also showed that the gas in the galaxy`s "outskirts," high above its spiral disk of stars, is not a single, smooth halo-like envelope, but instead forms smaller, discrete features. One of these features is arc-like, rising more than 11,000 light-years above the disk.
The background galaxy, and the fact that it is aligned with its radio jets perpendicular to UGC 10288`s disk, provides a valuable means of studying the nearer galaxy.
Jayanne English, of the University of Manitoba, said that they can use the radio waves from the background galaxy, coming through the nearer one, as a way to measure the properties of the nearer galaxy.
The study has been published in the Astronomical Journal.