Free Astronomy Magazine May-June 2016

SPACE CHRONICLES W MKO Support Astronomer Marc Kassis inspects the electronics cabinet at the rear of MOSFIRE shortly after its delivery to the Keck I tele- scope’s Nasmyth deck. [W.M. Keck Observatory] n wavelength picture of their galaxies: from rest-frame ultraviolet to rest- frame far-infrared. They looked at various observables that are commonly used to estimate the star-formation rates in galaxies and compare them with each other. These star-formation rate estimators include the ultraviolet light that is emitted from young stars, the infra- red light that shows how much of the ultraviolet light was absorbed by dust, and the nebular emission lines that are caused by young stars mak- ing the clouds of gas around them glow and radiate. These diagnostics have been observed and tested for local galaxies extensively in the past decade, but for distant galaxies it is challenging to acquire complete mul- ti-wavelength datasets. This study makes the first direct com- parison between the optical emis- sion line and the ultraviolet and in- frared tracers of star formation and indicates that, despite the under- lying uncertainties, astronomers can trust the nebular emission lines as robust indicators of the star-forma- tion rate and the amount of light that is obscured by dust in distant galaxies. These results help to build the foun- dations of galaxy evolution studies; in other words, help predict a phys- ical quantity (in this case, the star- formation rate) of a distant galaxy from the light that our telescopes capture. This analysis is part of the MOSFIRE Deep Evolution Field (MOS- DEF) survey, which is conducted by astronomers at UC Riverside, UCLA, UC Berkeley, UC San Diego. The MOSDEF team uses the MOSFIRE spectrometer on the the W. M. Keck Observatory telescopes to obtain spectra for many galaxies that are located at 1.5 to 4.5 billion years after the Big Bang, the interval in which the universe formed the high- est amount of stars in its history. The goal of the survey is to study the stellar, gaseous, and blackhole con- tent of galaxies at this important era in the history of the universe.