Conditions for detecting population III galaxies with next-generation telescopes

Abstract: Through the spectral synthesis model YGGDRASIL, developed by E. Zackris- son et al. 2011, luminosities for the chemically pristine population III galaxies are retrieved and compared to the capabilities of the upcoming infrared telescopes, in particluar the Wide Field InfraRed Survey Telescope (WFIRST). In order to push the very faint galaxies into the detectable regime of the telescope, magnification by gravitational lensing needs to be introduced. The probabilities for the nec- essary magnifications at different redshifts in combination with the depth of the telescope are translated into required minimum number densities and minimum formation rates for detecting one object per survey area. Both photometric and spectroscopic detections are investigated and compared to limits predicted by theory. Three different initial mass functions (IMF) for the stars that make up the galaxy are used, two that are top-heavy, i.e centers around stellar masses of 10 − 500M⊙, and one that resembles the IMF that are used for stars of younger generations, with its distribution peak at below one solar mass. The most optimistic results comes from the model that focusses on a galaxy of very heavy stars (with a total galaxy mass of 105 − 106M⊙), that yields minimum number densities for photometric detection at z > 10 that are lower or comparable to what has been predicted by theory. When the calculations are concerned with spectroscopy, the minimum number densities goes up and very massive galaxies (107M⊙) are required to reach the predicted limits at z > 10 and to enable detection by WFIRST. A comparison between the upcoming infrared telescopes; WFIRST, James Webb Space Telescope (JWST) and Euclid, are performed with WFIRST as the strongest candidate for photometry and JWST as the preferred instrument for spectroscopy, with a strong dependence on the survey area.