galaxies and the UV radiation budget

[No posts for a while as I have been out sick. I was only in for two hours since Tuesday, to see this talk:]

Alice Shapley (Princeton) gave a data-packed talk about galaxies at redshift around 2 and 3. She reminded us that there is no more redshift desert around 2, which was a major issue in my graduate thesis work. She spent most of her talk estimating the contribution of high-redshift galaxies to the ionizing ultraviolet radation, which we know is there from, eg, the lyman-alpha forest, and which at an earlier epoch reionized the Universe (but substantially after the Universe recombined from the primordial electron-positron plasma). Though there are huge uncertainties, and no sample of galaxies is large enough and well-enough studied to give a definitive answer, it does appear that the high-redshift galaxies release enough ultraviolet light into intergalactic space to make up most of the ionizing background radiation. In other news, she showed some reasonable (though admittedly not air-tight) evidence that the mass–metallicity relation is much less metal-rich at redshift 3 than at the present day (or than at redshift 1, which Moustakas, a few months ago, showed us was also less metal-rich than the present day).