Royal Astronomical Society | 2017 Jan 11
[img3="The artistic impression shows a Milky Way type galaxy in the local Universe, surrounded by a much larger halo of blue, faint light, made of Lyman-alpha photons. Credit: ESO/L. Calçada"]http://www.ras.org.uk/images/stories/pr ... 06_12.jpeg[/img3][hr][/hr]Astronomers led by David Sobral and Jorryt Matthee, of the Universities of Lancaster in the UK and Leiden in the Netherlands, have discovered giant halos around early Milky Way type galaxies, made of photons (elementary particles of light) that have struggled to escape them. ...
In order to understand how our own Milky Way galaxy formed and evolved, astronomers rely on observing distant galaxies. As their light takes billions of years to reach us, telescopes can be used as time machines, as long as we have a clear indicator to pinpoint the distance to the objects being observed. As with closer galaxies, stars, and planets, astronomers use the technique of spectroscopy to analyse their light, dispersing it into a spectrum.
Scientists then look for characteristic features (spectral lines) that tell them about properties including the composition, temperature, and movement of the object. With the most distant galaxies, only one spectral feature typically stands out, the so-called Lyman-alpha line associated with hydrogen gas.
Jorryt Matthee comments: "Newly born stars in very distant galaxies are hot enough to break apart hydrogen in surrounding clouds of gas, which then shines brightly in Lyman-alpha light, in theory the strongest such features observable in a distant galaxy. Yet in practice, Lyman-alpha photons struggle to escape galaxies as gas and dust block and diverge their travel paths, making it a complex process to understand." ...
The CALYMHA survey: Lyα luminosity function and global escape fraction of Lyα photons at z = 2.23 - David Sobral et al
- Monthly Notices of the RAS 466(1):1242 (2017 Apr 01) DOI: 10.1093/mnras/stw3090
arXiv.org > astro-ph > arXiv:1609.05897 > 19 Sep 2016 (v1), 25 Nov 2016 (v2)
- Monthly Notices of the RAS 458(1):449 (2016 May 01) DOI: 10.1093/mnras/stw322
arXiv.org > astro-ph > arXiv:1602.02756 > 08 Feb 2016