This theoretical scenario for galaxy formation is based on the numerical simulations presented by Dekel et al., 2009 (Nature, 457, 451D). However, the actual process of stream accretion onto a galaxy has never been directly observed and it remains speculative. Credits: ESA–AOES Medialab. HI-RES JPEG (Size: 1476 kb)
Herschel now shows that this is not the case by looking at galaxies that are very far away and thus seen as they were billions of years ago.
David Elbaz, CEA Saclay, France, and collaborators have analysed the Herschel data and find that galaxy collisions played only a minor role in triggering star births in the past, even though some young galaxies were creating stars at furious rates.
By comparing the amount of infrared light released at different wavelengths by these galaxies, the team has shown that the star birth rate depends on the quantity of gas they contain, not whether they are colliding.
Gas is the raw building material for stars and this work reveals a simple link: the more gas a galaxy contains, the more stars are born.
This applies to today's galaxies because, after forming stars for more than 10 billion years, they have used up most of their gaseous raw material.
The research paints a much more stately picture of star births than before, with most galaxies sitting in space, growing slowly and naturally from the gas they attract from their surroundings.
"Herschel was conceived to study the history of star formation across cosmic time", says Göran Pilbratt, ESA Herschel Project Scientist.
"These new observations now change our perception of the history of the Universe."
Notes for Editors
'GOODS–Herschel: an infrared main sequence for star-forming galaxies' by D. Elbaz et al. is published in Astronomy & Astrophysics, 533, A119. It is available online at:
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