Free Astronomy Magazine September-October 2015

SPACE CHRONICLES This radiation is emitted at a wave- length of 158 mi- crometres, and by the time it is stret- ched by the expan- sion of the Universe arrives at ALMA at just the right wave- length for it to be detected at a wave- length of about 1.3 millimetres. They were also not looking for the ex- tremely brilliant rare objects — such as quasars and gal- axies with very high rates of star for- mation — that had been seen up to now. Instead they concentrated on rather less dramat- ic, 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 car- bon. However, this glow wasn’t coming from the centre of the gal- axy, but rather from one side. Co- author Andrea Ferrara (Scuola Nor- male Superiore, Pisa, Italy) explains the significance of the new findings: “This is the most distant detection ever of this kind of emission from a ‘normal’ galaxy, seen less than one billion years after the Big Bang. It gives us the opportunity to watch the build-up of the first galaxies. For the first time we are seeing early galaxies not merely as tiny blobs, but as objects with internal struc- ture!” The astronomers think that the off-centre location of the glow is because the central clouds are being disrupted by the harsh en- vironment created by the newly formed stars — both their intense radiation and the effects of super- nova explosions — while the carbon glow is tracing fresh cold gas that is being accreted from the intergalac- tic medium. By combining the new ALMA obser- vations with computer simulations, it has been possible to understand in detail key processes occurring within the first galaxies. The effects of the radiation from stars, the survival of molecular clouds, the escape of ion- ising radiation and the complex struc- ture of the inter- stellar medium can now be calculated and compared with observation. BDF 3299 is likely to be a typical exam- ple of the galaxies responsible for re- ionisation. “We have been trying to under- stand the interstel- lar medium and the formation of the re- ionisation sources for many years. Fi- nally to be able to test predictions and hypotheses on real data from ALMA is an exciting moment and opens up a new set of questions. This type of obser- vation will clarify many of the thorny problems we have with the forma- tion of the first stars and galaxies in the Universe,” adds Andrea Ferrara. Roberto Maiolino concludes: “This study would have simply been im- possible without ALMA, as no other instrument could reach the sensitiv- ity and spatial resolution required. Although this is one of the deepest ALMA observations so far it is still far from achieving its ultimate capa- bilities. In future ALMA will image the fine structure of primordial gal- axies and trace in detail the build-up of the very first galaxies.” T his view is a combination of images from ALMA and the Very Large Telescope. The central object is a very distant galaxy, la- belled BDF 3299, which is seen when the Universe was less than 800 million years old. The bright red cloud just to the lower left is the ALMA detection of a vast cloud of material that is in the process of assembling the very young galaxy. [ESO/R. Maiolino] n