ASTROWATCH Spitzer Sees Light from the Very First Stars

ASTROWATCH

Compiled by Marc Turler, INTEGRAL Science Data Centre and Geneva Observatory Spitzer sees light from the very first stars

Deep observations with NASA's Spitzer Space Nature, they discuss all other possible sources Telescope have revealed infrared background of these infrared background fluctuations: from anisotropies that can be attributed to emission instrumental artefacts to distant unresolved from the very first stars in the universe. The galaxies or clusters, including solar-system diffuse glow detected by Spitzer would have zodiacal light and galactic emission from been emitted more than 13 billion years ago interstellar clouds. They conclude that the by the first generation of stars, which are angular size of the anisotropies is significantly believed to have been more than a hundred different from what is expected from sources in times more massive than the Sun and to have the solar system and in our galaxy, and that lived for only a few million years before their amplitude is too large to be due to exploding as the first supernovae. unresolved faint galaxies. The fluctuations are Stars of the very first generation in the also rather independent of the parameters universe - made only of primordial hydrogen used to remove foreground objects. and helium - are called Population III stars. The relatively large amplitude (of the order The absence of heavy chemical elements Spitzer infrared (3.6 /jm) image of stars and of 10%) of the anisotropies could result from allows them to reach masses and sizes well galaxies in the Draco constellation (top) and the fact that the era of Population III stars beyond those of the metal-rich Population I the resulting image showing the infrared lasted only about 300 million years and that stars - like our Sun - and the older background fluctuations (enhanced for the very bright stars are forming at the peaks Population II stars, which are poorer in metal. clarity) after masking out all stars, galaxies of the density field, which has been strongly These early giant stars, with masses of several and artefacts (bottom). The anisotropies have amplified since the time of the cosmic hundred solar masses, have so far never been a typical size of 1-2 arcmin and could be due microwave background emission by the seen in galaxies observable today. Even the to the glow of the first stars in the universe. gravitational pull of dark matter. A more Hubble Ultra Deep Field has only seen (NASA/JPL-Caltech/A Kashlinsky (GSFC).) detailed comparison of the results, with galaxies with stars already enriched in heavy theoretical models predicting the level of elements such as carbon and oxygen; and Hubble Space Telescope in 2013. fluctuations during the Population III era, will there are now doubts on the true nature and Now, rather unexpectedly, A Kashlinsky and have to await forthcoming papers that are distance of the candidate Population III collaborators claim they have already had a likely to be based on better results extracted galaxy, which was thought to be the farthest glimpse at those unknown territories with the from longer-exposure images. It is nevertheless known galaxy at a redshift of 10 (CERN modest 85 cm Spitzer Space Telescope. exciting to think that an 85 cm telescope was Courier May 2004 pl3). It therefore seems Removing the emission of all foreground stars able to detect the light emitted only a few that the detection of the very remote first stars and galaxies in deep infrared observations, hundred million years after the big bang by the and galaxies emerging from the "dark ages" at they identified fluctuations of the background very first stars lighting up the universe. redshifts of about 10 to 30 will require next- radiation on larger scales, which could be generation facilities like the James Webb attributed to the diffuse light from the Further reading Space Telescope, which should replace the Population III era. In an article published in A Kashlinsky etal. 2005 Nature 438 45.

Pictures of the month

Images from ESO's Very Large Telescope reveal the surroundings of a super-massive black hole in the centre of NGC 1097, a spiral galaxy located about 45 million light-years away in the southern constellation Fornax (the furnace). The inner ring (enlarged in the middle image) is a region of intense star formation surrounding the active nucleus at the centre. A masking process was applied on the infrared image (right) to suppress the stellar light of the galaxy, thus revealing spiral arms channelling gas and dust to the super-massive black hole at the heart of the galaxy. (ESO.)

10 CERN Courier December 2005