Gemini Observatory - GMOS-S Commissioning Team HCG 87 imaged with GMOS-S |
Hubble Heritage Team/STScI/AURA/NASA HCG 87 imaged with the Hubble Space Telescope |
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During commissioning in early 2003 of the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South Telescope, images and spectra were obtained of the group of galaxies known as the Hickson Compact Group 87 (HCG 87). The Gemini image (shown, left) compares very favorably with the Hubble Space Telescope Heritage image of this same field and illustrates the remarkable resolution that is possible with Gemini when atmospheric conditions are optimal. The three Gemini images used to make the color composite image have resolutions between 0.36 and 0.5 arcseconds (full-width-half-max) and an unsharp mask has been applied to highlight details in the major galaxies. Technical details on the images can be found here. |
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About Hickson Compact Group 87: One of the primary galaxies of the HCG87 group is an edge-on galaxy with dust lanes, which is a beautiful example of a box/peanut shaped central bulge that the eye perceives as an X-shaped structure. This morphology is due to the vertical instability of the orbits of millions of stars going around the center of the galaxy. This can be caused by interactions with other galaxies, including the accretion of dwarf galaxy companions, or by the presence of a bar-shaped structure. Thin bars are unstable structures that buckle about their midpoints out of the plane of the bar. The warp in the disk of the galaxy and the lack of a clear bar signature in the galaxy's spectrum suggest that the X-structure in this galaxy is due to an interaction. The image also includes other galaxies including a more face-on spiral and an elliptical. All of these galaxies move through space together and perform a slow graceful gravitational dance as they evolve and influence each other's structure. References: "The Nature of Boxy/Peanut-Shaped Bulges in Spiral Galaxies". Bureau, M.; Freeman, K. C. The Astronomical Journal, 118, 126-138, July 1999. "A Merger Origin for X Structures in S0 Galaxies". Mihos, J. Christopher; Walker, Ian R.; Hernquist, Lars; Mendes de Oliveira, Claudia; Bolte, Michael. The Astrophysical Journal Letters, 447, L87, July 1995. "Orbital dynamics of three-dimensional bars - III. Boxy/peanut edge-on profiles". Patsis, P. A.; Skokos, Ch.; Athanassoula, E. The Monthly Notice of the Royal Astronomical Society, 337, 578-596, December 2002. |
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Gemini Observatory |
Sample GMOS-S Longslit Spectrum of HCG87a
A longslit spectrum of HCG87a (box/peanut galaxy). The slit was placed along the major axis (long dimension) of the galaxy and the light was dispersed with a 400 line/mm diffraction grating to detect three emission lines from gas in the galaxy. Halpha is the brightest line emitted by Hydrogen gas at 6563A. The [NII] lines are emitted by ionized nitrogen gas. Doppler shift due to movement of the gas causes the observed wavelengths of the lines to shift with position along the slit. The gas to the rights of the galaxy's center is moving away from us at 350 km/sec with respect to the center of the galaxy while gas to the left is moving towards us. This shows that the galaxy is rotating. The bright vertical spectrum along the right edge is from a nearby star. The horizontal lines along the top of the image are emission lines from gas in the earth's atmosphere. |
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Gemini Observatory |
Electronics Engineer Benjamin Irarrazaval works on the Gemini South Multi-Object Spectrograph in the Gemini Instrument Lab on Cerro Pachon, Chile. |
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Gemini Observatory |
Electronic Systems Manager Rolando Rogers inspects the Gemini Multi-Object Spectrograph's filter wheel at the Gemini Instrument Lab on Cerro Pachon Chile. |
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Gemini Observatory |
Instrument Technician Luis Solis works on the Gemini Multi-Object Spectrograph at Gemini South in Chile. |
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Gemini Observatory |
GMOS mounted on the up-looking port of a Gemini telescope. Photo Credit: Gemini Observatory. |
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