Image Credit: NASA, ESA, and F. Courbin (EPFL, Switzerland) |
Astronomers
using NASA’s Hubble Space Telescope have found several examples of
galaxies containing quasars, which act as gravitational lenses,
amplifying and distorting images of galaxies aligned behind them.
Quasars
are among the brightest objects in the universe, far outshining the
total starlight of their host galaxies. Quasars are powered by
supermassive black holes.
To
find these rare cases of galaxy-quasar combinations acting as lenses, a
team of astronomers led by Frederic Courbin at the Ecole Polytechnique
Federale de Lausanne (EPFL, Switzerland) selected 23,000 quasar spectra
in the Sloan Digital Sky Survey (SDSS). They looked for the spectral
imprint of galaxies at much greater distances that happened to align
with foreground galaxies. 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.
The
team involved in this research includes: F. Courbin, C. Faure, F.
Rerat, M. Tewes, and G. Meylan (EPFL, Switzerland), S.G. Djorgovski, A.
Mahabal (Caltech), D. Stern (JPL), T. Boroson (NOAO), D. Sluse (Bonn
University, Germany), R. Dheeraj (University of Maryland). The full
study is presented in the journal Astronomy and Astrophysics.
The
Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency. NASA’s Goddard Space Flight
Center in Greenbelt, Md., manages the telescope. The Space Telescope
Science Institute (STScI) in Baltimore, Md., conducts Hubble science
operations. STScI is operated by the Association of Universities for
Research in Astronomy, Inc., in Washington, D.C.
Images and more information about Hubble and this study
Source: NASA Goddard Space Flight Center
