The contribution of the faint Lyman alpha galaxies to cosmic reionization as seen by MUSE/VLT
Speaker: TRAN Thi-Thai (Division of Science, NAOJ)
Abstract:
At the end of the Dark Ages, when the first structures of the Universe were formed, radiation from these structures ionized the neutral hydrogen atom surrounding its environment. This crucial phase is known as cosmic re-ionization. It is the last phase transition undergone by the Universe, finishing around z~6. Today, various hypotheses exist concerning the main contributors to this process, such as Active Galactic Nuclei (AGN), star-forming galaxies, etc. I assess the contribution of the star-forming galaxies to cosmic reionization by studying the evolution of the luminosity function with redshift, estimating their star formation rate density as well as the escape fraction of Lyman alpha photon at different redshift ranges through the use of VLT/MUSE as well as gravitational lensing. For this purpose, the work assembles the largest sample of lensed Lyman-alpha emitters: faint galaxies identified by the Lyman-α emission line (LAEs) to date (at redshifts between 2.9 and 6.7). The best-fit results of the Schechter function at different redshift ranges allow us to determine the luminosity density and convert it to the star formation rate density. These results, compared with those of the critical value for the star formation density, suggest that galaxies selected by their Lyα emission could be responsible for reionization assuming a Lyα photon escape fraction of 8%, with a typical clumping factor of ∼ 3. On the other hand, when assessing the escape fraction of Lyman alpha photons from star-forming galaxies we found that the LAE population could have provided all the photons necessary for reionisation at z=6 using well-motivated assumptions about the ionising photon efficiency and the escape of ionising photons from these galaxies.