ISO search for early galaxies

Through two windows on the early Universe, in opposite directions in the sky, ESA's Infrared Space Observatory (ISO) detects remote galaxies glowing in infrared light. ISO's ISOCAM camera stared for hours at regions known to be clear of obscuring clouds of gas and dust. Some objects recorded here date from when the Universe was a third of its present age. In the left image, ISOCAM results are superimposed on a Hubble Space Telescope image. Twenty galaxies conspicuous at an infrared wavelength of 15 microns are likely to be experiencing starbursts. Seven objects that reveal themselves only at 7 microns are elliptical galaxies, showing up in the infrared because of the redshift. Beyond the edges of the Hubble image, ISOCAM has registered another 26 distant galaxies, six of which are still undetected by visible light. The right image shows the southern deep field as observed by ISOCAM at 15 microns. Astronomers consider 22 to 30 objects to be distant galaxies. As in the northern field, many are expected to be starbursts. Hubble has not yet looked through this window, but the 4-m telescope at CTIO, Chile, has done so, and one ISO object (arrowed here) is so far unseen in visible light. This object is likely to be undergoing an especially violent period of star formation. [Image Date: 1998/04] [98.04.006-002]