Looking Sharp: Images from New Gemini Spectrograph rival view from space

Gemini Observatory’s new spectrograph, without the help of adaptive optics, recently captured images that are among the sharpest ever obtained of astronomical objects from the ground.

Along with the images and spectra acquired during recent commissioning of the Gemini Multi-Object Spectrograph (GMOS) on the 8-metre Gemini South Telescope in Chile, one image is particularly compelling. This Gemini image reveals remarkable details, previously only seen from space, of the Hickson Compact Group 87 (HCG87). HCG87 is a diverse group of galaxies located about 400 million light years away in the direction of the constellation Capricornus. A striking comparison with the Hubble Space Telescope image of this object, including resolution data, can be viewed at http://www.gemini.edu/media/images_2003-3.html

“Historically, the main advantage of large ground-based telescopes, like Gemini, is the huge mirrors that collect significantly more light for spectroscopy than is possible with a telescope in space,” said Phil Puxley, Gemini Associate Director of the Gemini South Telescope located on Cerro Pachón, Chile. He explains “The Hubble Space Telescope is able to do things that are impossible from the ground. However, ground-based telescopes like Gemini, when conditions are right, approach the quality of optical images now only possible from space. One key area – spectroscopy of faint objects, which requires large apertures and fine image quality – is where large telescopes like Gemini provide a powerful, complementary capability to space-based telescopes.”

GMOS was built as a joint partnership between Gemini, Canada and the UK at a cost of over £3 million. Separately, the U.S. National Optical Astronomy Observatory provided the detector subsystem and related software. The instrument was built by a group of astronomers and engineers from the UK Astronomy Technology Centre in Edinburgh, Durham University and the Hertzberg Institute of Astrophysics in Canada.

GMOS-South is currently undergoing commissioning on the 8-metre Gemini South Telescope at Cerro Pachon, Chile. “GMOS-S worked right out of the box, or rather, right out of the 24 crates that brought the 2-tonne instrument to Chile from Canada and the UK – just like its northern counterpart did when it arrived on Hawaii’’s Mauna Kea, ” says Dr.Bryan Miller, head of the commissioning team. The GMOS programme demonstrates the advantage of building two nearly identical instruments. Experience and software from GMOS-North have helped us commission this instrument more rapidly and smoothly than we could have done otherwise,” explains Dr Miller. He adds, “Although the images from GMOS are spectacular, the instrument is primarily a spectrograph and that is where its capabilities are most significant for scientists.” GMOS-South is expected to begin taking science data in August 2003.

As a multi-object spectrograph, GMOS is capable of obtaining hundreds of spectra in one “snapshot.” The ability to deliver high-resolution images is a secondary function. “It used to take an entire night to obtain one spectrum,” explains Dr. Inger Jørgensen who led the commissioning of the first GMOS instrument on the Frederick C. Gillette Gemini Telescope over a year ago. “With GMOS, we can collect 50-100 spectra simultaneously. Combined with Gemini’’s 8-metre mirror, we can now efficiently study galaxies and galaxy clusters at vast distances – distances so large that the light has travelled for half the age of the Universe or more before reaching Earth. This capability presents unprecedented possibilities for investigating how galaxies formed and evolved in the early Universe.”

GMOS achieves this remarkable sensitivity partly because of its technologically advanced detector, which consists of over 28 million pixels, and partly because of multiple innovative features of the Gemini dome and telescope that reduce local atmospheric distortions around the telescope. “When we designed Gemini, we paid careful attention to controlling heat sources and providing excellent ventilation,” said Larry Stepp, former Gemini Optics Manager. Stepp elaborates, “For example, we constructed 3-story high vents on the sides of the Gemini enclosures. It is great to see this image that provides such a dramatic validation of our approach.”

Dr Rob Ivison, GMOS Project Scientist at the UK Astronomy Technology Centre in Edinburgh,
said “The Gemini Observatory and its powerful new instrument, gives UK astronomers a unique opportunity to investigate the zoo of galaxies, piecing together the sequence of events that lead to the universe we see today. We can begin our painstaking detective work, peering through time to an age when the earth was nothing but a bunch of primordial atoms, long before our solar system formed, when the first stars and galaxies were lighting up the universe.”

The twin Gemini Telescopes offer a unique advantage, explains Director of the Gemini Observatory Dr Matt Mountain. “Now that both telescopes are equipped with nearly identical GMOS instruments, we have created an unprecedented uniform platform to coherently study and take deep spectra of any object in the northern or southern sky at optical wavelengths.”

Dr Adrian Russell, Director of the UK Astronomy Technology Centre in Edinburgh adds to this,
“With the on schedule delivery and successful commissioning of GMOS-S, for the first time the Gemini twins can act as one, allowing a co-ordinated study of the entire sky.”

Upgrades to GMOS-S that will increase its variety of capabilities are planned even as the instrument is undergoing commissioning. An Integral Field Unit (IFU) on GMOS-S is anticipated to begin commissioning in early 2004.

Like GMOS-N, which has already received and commissioned its IFU, the IFU on GMOS-S will greatly enhance its spectra collection abilities, such as probing the dynamics of active galactic nuclei. Jeremy Allington-Smith, leader of the IFU team at the University of Durham said:
“GMOS-S will soon be fitted with an integral field unit like its sister in the north. Made by the University of Durham, it uses more than a thousand optical fibres, tipped at each end with microscopic lenses, to dissect the object under study. This gives GMOS a 3-D view of the target, in which each pixel in the image is replaced by a spectrum. This innovation allows GMOS to make detailed maps of, for example, the motion of stars and gas in galaxies.”