An international team of astronomers using NASA’s Hubble Space Telescope has discovered several galaxies containing quasars, which act as gravitational lenses, amplifying and distorting images of galaxies aligned behind them.
Galaxy SDSS J1005+4016 contains quasar acting as gravitational lense (NASA / ESA / F. Courbin / EPFL)
According to the Hubble website, to find these rare cases of galaxy-quasar combinations acting as lenses, the team led by Dr. Frederic Courbin of the Ecole Polytechnique Federale de Lausanne (EPFL, Switzerland) selected 23,000 quasar spectra in the Sloan Digital Sky Survey (SDSS). The findings will appear in the journal Astronomy & Astrophysics.
The team looked for the spectral imprint of galaxies at much greater distances that happened to align with foreground galaxies.
Galaxies SDSS J0919+2720, SDSS J1005+4016 and SDSS J0827+5224 contain quasars acting as gravitational lenses: gravitational arcs and rings indicated by the arrows (NASA / ESA / Z. Levay / STScI)
Once candidates were identified, Hubble’s sharp view was used to look for gravitational arcs and rings (which are indicated by the arrows in these three Hubble photos) that would be produced by gravitational lensing.
Quasar host galaxies are hard or even impossible to see because the central quasar far outshines the galaxy. Therefore, it is difficult to estimate the mass of a host galaxy based on the collective brightness of its stars. However, gravitational lensing candidates are invaluable for estimating the mass of a quasar’s host galaxy because the amount of distortion in the lens can be used to estimate a galaxy’s mass.
The next step for the team is to build a catalog of “quasar-lenses” that will allow them to determine masses for a statistically significant number of quasar host galaxies and to compare them with galaxies without quasars.
With the numerous wide-field surveys that will start in the near future or that are already started, hundreds of thousands of quasars will be accessible for looking for lensing effects.
