Thesis

A large double-blind Lyα-Hα survey at z~2.2: what does Lyα really tell us?

• Call:

  IDPASC Portugal - PHD Programme 2014

• Academic Year:

  2014 /2015

• Domain:

  Astrophysics

• Supervisor:

  David Sobral

• Co-Supervisor:

• Institution:

  Faculdade de Ciências - Universidade de Lisboa

• Host Institution:

  Faculdade de Ciências - Universidade de Lisboa

• Abstract:

  An extremely large number of studies rely on the Hydrogen Lyman-α (Lyα) emission line to survey, study and understand the distant Universe (z>2-3), as it is often the only feature available to spectroscopically confirm/study such galaxies. However, the escape fraction of Lyα (fescape) is highly uncertain at z>2, and much is unknown about what Lyα actually traces. How much are we missing by relying on it? How biased is our current view of the very high redshift, almost completely based on Lyα? Can we finally calibrate and understand Lyα and Lyα emitters? In order to answer such questions, the student will conduct and work on very large (~5-10 deg2 surveys at z~2-3 (the likely peak of the star-formation history). This includes a perfectly matched) Lyα-Hα survey at z=2.23 using custom-made narrow-band filters specifically designed for this project (the first has already been delivered to the INT; PI: D. Sobral). By measuring Lyα/Hα ratios for a sample of hundreds of galaxies at z=2.23, the student will robustly measure fescape and the Lyα/Hα ratio as a function of mass, colour, environment and SFR and empirically calibrate Lyα for the first time, with very important applications/consequences for z>2 studies. The student will also lead the follow-up (using e.g. X-shooter and VIMOS on the VLT – some data already being taken) of many of the sources, resulting in the addition of accurate metallicity and dust extinction measurements (from a wealth of emission-line ratios). This will be a significant contribution towards unveiling the nature of Lyα emitters with a large, representative sample. Furthermore, by conducting by far the largest survey (>2-4 orders of magnitude larger in volume than any other) for the most luminous Lyα emitters at z~2-3, the student will also detect >3000 powerful Lyα emitters and >100 Lyα “blobs” (the largest ~contiguous objects found in the Universe, many times the size of a single galaxy), determine their Luminosity Function for the first time and measure their correlation function and evolution. This will provide the first robust sample that can be directly compared with the highest redshift samples, to directly test whether there is evolution in the bright end of the Lyα luminosity function. This project will allow the student to observe on large telescopes to obtain the data directly (~20-40 nights over the first years), but also to do follow-up studies with e.g. VLT or ALMA to unveil and detail the nature of misterious Lyα emitters and blobs.