Galaxy ‘Hunting’ Made Easy – Galaxies found under the Glare of Cosmic  Flashlights

Astronomers using ESO’s Very Large Telescope have discovered in a  single pass about a dozen otherwise invisible galaxies halfway across  the Universe. The discovery, based on a technique that exploits a  first-class instrument, represents a major breakthrough in the field  of galaxy ‘hunting’.

The team of astronomers led by Nicolas Bouche have used quasars to  find these galaxies. Quasars are very distant objects of extreme  brilliance, which are used as cosmic beacons that reveal galaxies  lying between the quasar and us. The galaxy’s presence is revealed by  a ‘dip’ in the spectrum of the quasar – caused by the absorption of  light at a specific wavelength.

The team used huge catalogues of quasars, the so-called SDSS and 2QZ  catalogues, to select quasars with dips. The next step was then to  observe the patches of the sky around these quasars in search for the  foreground galaxies from the time the Universe was about 6 billion  years old, almost half of its current age.

“The difficulty in actually spotting and seeing these galaxies stems  from the fact that the glare of the quasar is too strong compared to  the dim light of the galaxy,” says Bouche.

This is where observations taken with SINFONI on ESO’s VLT made the  difference. SINFONI is an infrared ‘integral field spectrometer’ that  simultaneously delivers very sharp images and highly resolved colour  information (spectra) of an object on the sky.

With this special technique, which untangles the light of the galaxy  from the quasar light, the team detected 14 galaxies out of the 20  pre-selected quasar patches of sky, a hefty 70% success rate.

“This high detection rate alone is a very exciting result,” says  Bouche. “But, these are not just ordinary galaxies: they are most  notable ones, actively forming a lot of new stars and qualifying as  ‘starburst galaxies’.”

“We discovered that the galaxies located near the quasar sightlines  are forming stars at a prodigious rate, equivalent to 20 suns per  year,” adds team member Celine Peroux.

These findings represent a big leap forward in the field, setting the  stage for a very promising era of galaxy ‘hunting’.

The astronomers now plan to use SINFONI to study in more detail each  of these galaxies, by measuring their internal motions.

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The full text of this release, along with the images, is available at http://www.eso.org/public/outreach/press-rel/pr-2007/pr-40-07.html

SINFONI is a combination of a novel infrared ‘integral field  spectrometer’ (SPIFFI) and a special adaptive optics module (MACAO).  The integral field module SPIFFI gives detailed colour, or spectral,  information for each of 2000 spatial points on the sky, arranged over   a contiguous two dimensional field of 32 times 64 pixels. SINFONI was  developed and built by an international consortium consisting of the  Max Planck Institute for Extraterrestrial Physics, Garching, Germany,  ESO, and NOVA, Leiden, the Netherlands (see ESO PR 21/04).

The team is composed of Nicolas Bouche, Richard Davies, Frank  Eisenhauer, Natascha M. Förster Schreiber, and Linda Tacconi (Max  Planck Institute for Extraterrestrial Physics, Garching, Germany),  Michael T. Murphy (Swinburne University of Technology, Australia),  and Celine Peroux (ESO).

  Science Contacts

Nicolas Bouche
Max Planck Institute for Extraterrestrial Physics, Garching, Germany
Phone: +49 89 30000 3830
Email: nbouche@mpe.mpg.de

Celine Peroux
ESO, Garching, Germany
Email: cperoux@eso.org

Michael T. Murphy
Centre for Astrophysics & Supercomputing
Swinburne University of Technology, Australia
Phone: +61 (0)3 9214 5818
Email: mmurphy@swin.edu.au