[warning Will Robinson: the voices in my head that used to help write Slacker Astronomy are forcing me to write in the genre of a sensationalized nature special]
One of the most elusive creatures speculated to lurk within the sky are the mysterious very high-redshift Lyman alpha emission galaxies. These systems, without the metal found in their more common and larger low-redshift cousins, are rich in hydrogen and slow in producing stars. Scientists had long speculated these systems had to exist, but despite 30 years of searching beyond the Lyman Alpha Forest, none of these systems had ever before been found.
Now, astronomers using the Very Large Telescope in Chile bring us word of a serendipitous discovery of 27 of these elusive systems. They were found quite by accident in a 92 hour spectral image that was being taken to look for faint intergalactic gas. According to UK astronomer Michael Rausch, “As often happens in science, we got a surprise and found something we weren’t looking for – dozens of faint, discrete objects emitting radiation from neutral hydrogen in the so-called Lyman alpha line, a fundamental signature of protogalaxies.”
The well respected Lyman Alpha line is from the esteemed hydrogen spectral series. His lazier (or at least lower energy) cousin, Balmer alpha (aka Hydrogen alpha) is known for hanging out in the “Open” signs at bars were he often glows red as his only electron jumps up to its 3rd energy level and then falls down to its second level, always losing a 1.9-eV, red photon in the process. Lyman Alpha is more energetic, and his high diving electron climbs up to level 2 and jumps 10.2 eV down while flinging an ultraviolet photon into space. Lyman alpha is perhaps most often found emitting light in hydrogen clouds being illuminated by hot young stars. More often, however, Lyman Alpha absorbs light instead of emitting it. Whole families of Lyman alpha absorbers lurk in the space between galaxies, in the form of gas clouds, and these systems create a messy forest of Lyman Alpha absorption lines in the spectra of background galaxies and quasars.
This new discover of Lyman Alpha emitters and their host extremely-distant galaxies adds one more piece to the galaxy construction puzzle. From the pieces that had already been put together, astronomers suspected the final image would show that small systems grow into large galaxies through the joining of gas unto gas and star unto star through the garivational bond of eternal mergered bliss. (This is very different from the frequently temporary bond of binary stars, which occasionally split violently. No known previously joined galaxies have been seen to come apart, although the poly-gactic joining of many systems into 1 system has been observed in many systems, including our own Milky Way galaxy).
“What makes our discovery particularly exciting is that it opens the route to find large numbers of building blocks of normal galaxies and that we will now be able to study in detail how galaxies like our Milky Way have come together,” says Martin Haehnelt.
It may be a long time before astronomers get a second glimpse at this elusive population. The 92 hours of VLT time necessary to obtain this first image of these very faint system took two years to obtain. Until another image is acquired, scientists will have to satisfy themselves with examining and re-examing these 27 systems to try and sort out what these galaxies are like and if the are the true genetic predecessors to the hydrogen rich damped Lyman alpha galaxies we find in more recent epochs.
Image Credit: ESO