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Far beyond Europe's Borders

The Millimetric Radio Astronomy Institute (IRAM)

The Pico Velata telescope (30 meters in diameter).

Light detected by even the largest optical telescopes must come from hot sources like the Sun, stars, or ionised gas and is observed either directly or by reflection off nearby cold bodies (comets, planets, and the like). Relying on the visible range therefore yields a very incomplete picture similar to photographs taken by a meteorological satellite at night: the shapes of the continents are barely visible, picked out by points of light which are cities. Interstellar matter with its very cold gas and dust makeup is virtually undetectable at visible wavelengths, as it emits no visible signal at – 230°K and below. At those temperatures dust and molecules give off only far-infrared and millimeter radiation. Far-infrared cannot be detected through Earth's atmosphere, which is where IRAM comes in with its telescopes specifically built to read in the millimetric range.

Perched at 2,850 meters of altitude, on Pico Velata in the Sierra Nevada range near Grenada, Spain, IRAM's 30-meter telescope is the largest antenna operating between 1 and 3 millimeters of wavelength in the world. The Pico Velata telescope is particularly well-suited to map large-area sources as well as those of weak intensity. It has contributed to the discovery of some twenty interstellar molecules, including several free radicals such as C8Hs and MgNC, that were not observed in earthbound laboratories. This facility has also uncovered molecules in comets, planets, and in Io and Titan, the moons of Jupiter and Saturn. When the comet Shoemaker-Levy collided with Jupiter, Pico Velata was able to observe the formation of CO, HCN, and CS resulting from the impact and to track these molecules' expansion in the planet's upper atmosphere. It has also started the study of the cold dust in the nearby galaxies, as in the most remote ones.

carte de l'émission thermique

© Réf : Guélin, Guilloteau et al. en prép.

Map of thermal emission of dust, recorded at 1.2 mm of wavelength by the Bure interferometer towards the quasar BR1202 (z = 4.69). The source continuum emission is resolved into two components, separated by 3", which are both detected in CO radiation (see spectra in inserts).


IRAM's interferometer on Plateau de Bure, 2,550 meters high in France's southern  Alps, is composed of six antennas each 15 meters in diameter, which can be moved along two perpendicular rail tracks, each 400 meters long. The large collective area, combined with the high-precision surface, makes it the most sensitive millimeter instrument in the world. It has made possible the systematic study of dust and molecular gas in high-redshift objects (meaning in objects pertaining to the young Universe). It is the only instrument to have detected the CO molecule in thirty or so galaxies and quasars whith redshifts z > 1, like BR 1202 (z=4.69) and J1148+5251 (z=6,42), the farthest molecular sources discovered to date. These observations deliver precious information on the dynamics, mass, and chemical composition (in some cases even on the isotopic composition) of galaxies when the Universe was just one-tenth or one-twentieth of its current age.

interféromètre de Bure

© IRAM

The interferometer on Plateau de Bure in the southern Alps, at 2,550 meters of altitude, comprises six antennas each 15 meters in diameter and movable along two perpendicular rails 400 meters long.


With the Bure interferometer astronomers can map even weak sources to a degree of resolution equal to that of the best ground-based optical telescopes, making it the instrument of choice for studying the formation of stars and planetary systems. The accretion and rejection activities associated with star formation can reach spectacular degrees of energy, with collimated gaseous jets and thin disks ringing the young star. The Bure interferometer is the only instrument currently capable of mapping these disks and jets in molecules other than CO, which in turn means that it can record the mass and chemical composition of celestial objects that are in many ways similar to the remains of the solar nebula just after the formation of the Sun.


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Summary

Contact

Michel Guélin
Institut de radioastronomie millimétrique (IRAM) et Laboratoire d'étude du rayonnement et de la matière en astrophysique (LERMA)
CNRS-Observatoire de Paris-ENS-Université de Cergy-Pontoise-Université Paris VI
E-mail: guelin@iram.fr

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