ESO Science Release | 2015 July 22
[imghover=http://cdn.eso.org/images/screen/eso1530b.jpg]http://cdn.eso.org/images/screen/eso1530a.jpg[/imghover][c]redit: ESO/R. Maiolino[/c][hr][/hr]The Atacama Large Millimeter/submillimeter Array (ALMA) has been used to detect the most distant clouds of star-forming gas yet found in normal galaxies in the early Universe. The new observations allow astronomers to start to see how the first galaxies were built up and how they cleared the cosmic fog during the era of reionisation. This is the first time that such galaxies are seen as more than just faint blobs.
When the first galaxies started to form a few hundred million years after the Big Bang, the Universe was full of a fog of hydrogen gas. But as more and more brilliant sources — both stars and quasars powered by huge black holes — started to shine they cleared away the mist and made the Universe transparent to ultraviolet light [1]. Astronomers call this the epoch of reionisation, but little is known about these first galaxies, and up to now they have just been seen as very faint blobs. But now new observations using the power of ALMA are starting to change this.
A team of astronomers led by Roberto Maiolino (Cavendish Laboratory and Kavli Institute for Cosmology, University of Cambridge, United Kingdom) trained ALMA on galaxies that were known to be seen only about 800 million years after the Big Bang [2]. The astronomers were not looking for the light from stars, but instead for the faint glow of ionised carbon [3] coming from the clouds of gas from which the stars were forming. They wanted to study the interaction between a young generation of stars and the cold clumps that were assembling into these first galaxies.
They were also not looking for the extremely brilliant rare objects — such as quasars and galaxies with very high rates of star formation — that had been seen up to now. Instead they concentrated on rather less dramatic, but much more common, galaxies that reionised the Universe and went on to turn into the bulk of the galaxies that we see around us now.
From one of the galaxies — given the label BDF 3299 — ALMA could pick up a faint but clear signal from the glowing carbon. However, this glow wasn’t coming from the centre of the galaxy, but rather from one side. ...
The assembly of "normal" galaxies at z=7 probed by ALMA - R. Maiolino et al
- Monthly Notices of the RAS 452(1) 54 (2015 Sep 01) DOI: 10.1093/mnras/stv1194
arXiv.org > astro-ph > arXiv:1502.06634 > 23 Feb 2015 (v1), 23 May 2015 (v2)