Extreme Ultraviolet (UV) light is blocked by our atmosphere (fortunately for us, because they are dangerous for our skin). Even from space it is very hard to measure. At the moment there is no single satellite telescope that can give information about this part of the spectrum. Bad news for astronomers, because they really want to know how many of such ionizing photons are emitted by massive stars. Such photons play a very important role in heating their surrounding clouds where low mass stars and their planets are still forming. These photons are also believed to have played a very big role early in the history of our Universe. They ionized the intergalactic H during the Cosmic Epoch of reionization. This made our universe transparent and ended the so-called Cosmic Dark Ages.
For this study we use a trick proposed by Scoville & Murchikova (2013) that allows to indirectly measure the extreme UV using ALMA. ALMA is an array of antennas in the dry desert of Chile (image), which can observe the sky in (sub)millimeter wavelengths, i.e. in wavelengths that are too red to see with the naked eye. Instead of measuring the ionizing photons directly, we will measure the effect they have on the surrounding H and He gas by measuring the “high-order recombination lines” that ALMA is sensitive too.
This proposal ALMA 2016.1.01015.S (PI De Mink) has been awarded 6.6 hours. The project design and analysis is lead by E. Muchicova (Caltech) under supervision of N. Scoville (Caltech). Image credit: Credit ALMA/NAOJ/NRAO J. Hills