Thesis

Unveiling the 3-D structure of distant super-clusters: the roles of environment, mass and galaxy properties at z~1

• Call:

  IDPASC Portugal - PHD Programme 2015

• Academic Year:

  2015 / 2016

• Domains:

  Cosmology | Astrophysics

• Supervisor:

  David Sobral

• Co-Supervisor:

• Institution:

  Faculdade de Ciências - Universidade de Lisboa

• Host Institution:

  FCUL/Institute of Astrophysics and Space Sciences

• Abstract:

  Why were galaxies in the distant Universe so efficient at producing new stars? What were the roles of “nature” (stellar mass) and “nurture” (environment) in the past, how did they change with cosmic time and is there a connection between those and the declining star formation activity? Is our current view of how galaxies form and evolve correct? By probing a very wide range of environments (from fields to clusters of galaxies) and masses, we are now obtaining a much better picture of the roles and inter-dependences of mass and environment in the distant Universe. However, there are significant limitations in current studies, due to the small sample sizes, lack of multi-wavelenght data in cluster fields, projection effects, and the dilution/confusion of environments (e.g. filaments vs small groups). In order to obtain the sharp view that we need, overcoming current limitations (from the use of photometric redshifts), the student will start by using the VLT (with VIMOS [PI: D. Sobral], 40 hours of observations already conducted at the VLT, all in excellent conditions) to accurately map in 3-D a unique super-structure at z = 0.84 in the COSMOS field (10×13 Mpc). This massive, large structure contains 3 confirmed massive X-ray clusters/groups and shows a striking filamentary structure of star-forming galaxies. With >1000 galaxies residing in such structure, the student will measure accurate redshifts (from both emission and absorption lines) and make a detailed/accurate 3-D map of the complex structure, identifying filaments, fields, outskirts, small groups and the cluster cores. The student will obtain independent mass estimates from the absorption lines, and map SFRs down to even the least active galaxies, but also detect post-starburst galaxies (K+As) and map their fraction in the cluster, group, filament and field environments over the entire structure. The unique modelling capabilities developed at IA-CAUP, will be fully implemented to interpret and extract even more information from the high S/N, high quality spectra. The results of this project will be directly compared with a large field survey, recently approved by ESO (LEGA-C, 128 nights on the VLT, Co-I: D. Sobral), will reveal exactly where star formation activity is being enhanced/quenched, clearly disentangling the roles of mass and environment in the distant Universe in a robust way for the first time. The student will then fully explore the rich multi-wavelenght data-set to detail and expand the conclusions of the study (including with SED-modelling/fitting), particularly by investigating the morphologies (with Hubble Space Telescope imaging), but also to look at radio and far-infrared (Spitzer + Herschel) properties of galaxies residing in the various environments within the super-structure and in the general field environment.