Intensive observing campaign in Spain to follow up ISO discoveries
24 May 2000The European Space Agency's ISO telescope was the first space observatoryrevealing the infrared 'face' of the Universe with high sensitivity, andby so doing pictured thousands of objects whose true nature is stillunknown. This month a network of European astronomers will try to learnmore about these new ISO sources, by observing many of them with about adozen ground-based telescopes, mainly at the observatories in theCanary Islands (Spain)."ISO has worked as a 'scoop' finder, and nowthere's a whole set of telescopes following up the news", says MartinKessler, ISO Project Scientist. The new ISO sources will soon also be observed with ESA's recently launched X-ray telescope, XMM-Newton.
Human eyes are blind to most types of light: they can't see infrared light, nor ultraviolet light... only the so-called (for obvious reasons) 'visible' light. Because different light reveals different phenomena, human vision misses part of the story, for example very dusty galaxies are invisible in 'visible' light but become very bright in the infrared. The astronomers' dream is to see all kinds of light, which is why a whole ISO observing programme was prepared in co-ordination with a network of ground-based telescopes that would try to 'see' at different wavelengths what ISO saw in the infrared.
The programme, called ELAIS (European Large Area ISO Survey), was a joint effort by 19 European institutions and over a hundred astronomers. It was one of ISO's longest observing programmes, using 360 hours of ISO's time, and focused on four large areas in the sky, three in the Northern Hemisphere and one in the South, plus six smaller regions.
As a result, about a thousand infrared sources were detected by ISO. Many of them have already been followed up with radio, visible, near infrared and submillimetre ground-based telescopes, thanks to which astronomers already know two things: that many sources are galaxies; and that some are especially interesting because so far only ISO has been able to detect them - they are either too faint, too far away or too dusty to be seen by other telescopes. These 'exclusive' ISO sources could be quasars - very distant and bright objects of still controversial nature - or maybe active but very dusty galaxies. The forthcoming observations will help to find out.
The observing campaign at the observatories of the Instituto de Astrofmsica de Canarias (Canary Islands, Spain) started on mid-May and will last till 3 August. It is especially aimed at obtaining spectra of the most interesting sources, which will tell astronomers what sort of objects ISO has found -quasar spectra are very different to the spectra of ordinary galaxies or starburst galaxies, for instance. Spectra will also elucidate the distances at which the objects lie.
"We have a lot of information already, but we need to know how far away the sources are to determine their intrinsic brightness, and how far into the Universe we are looking. We have been waiting a lot for these spectra!", says Stephen Serjeant, from the ELAIS team at the Imperial College in London.
The ELAIS team has been granted more than 30 observing nights by the International Scientific Committee of the Canarian observatories. They will observe with six telescopes, including the British/Dutch William Herschell Telescope (WHT), which allows to take spectra of hundreds of objects in just one night of observations, and the Italian Telescopio Nazionale Galileo.
Tthe team will also soon start observing soon with another telescope at Kitt Peak (Arizona) , equipped with a spectrograph similar to the one at the WHT, with two more telescopes in Hawaii; and with ESA's recently launched X-ray telescope, XMM-Newton.
"The amount of time we have is an indication of the importance of the project", says Ismael Pirez Fournsn, co-ordinator of the observations at the Canarian observatory. "The ELAIS fields are becoming more and more interesting because they are the fields covered at more wavelengths so far. Even current and future space telescopes will follow-up our observations".
About half of the ELAIS sources have been already published in an on-line catalogue at http://athena.ph.ic.ac.uk.
Ismael Pirez Fournsn, Instituto de Astrofmsica de Canarias
Tel: +34 922 605200
Stephen Serjeant, Imperial College London
Tel: +44 20 7594 7534
Martin Kessler, ISO project scientist
Tel: +34 91 8131253
Note to editors
The European Space Agency's infrared space telescope, ISO, operated from November 1995 till May 1998, almost a year longer than expected. As an unprecedented observatory for infrared astronomy, able to examine cool and hidden places in the Universe, ISO successfully made nearly 30 000 scientific observations.