Investigating Structure Formation around Massive Galaxies through a Radio-Infrared Synergy


  • Call:

    IDPASC Portugal - PHD Programme 2015

  • Academic Year:

    2015 / 2016

  • Domain:


  • Supervisor:

    José Afonso

  • Co-Supervisor:

  • Institution:

    Faculdade de Ciências - Universidade de Lisboa

  • Host Institution:

    Faculdade de Ciências - Universidade de Lisboa

  • Abstract:

    One of the greatest challenges facing observational cosmology is understanding the formation of large scale structure in the Universe. Hierarchical models for structure formation developed over the last few years, achieving the high degree of predictive success that they do, are however still unconstrained, in particular in helping to understand how the light (galaxies) traces the underlying (dark) matter and how this relation evolves over time. We will address this problem by performing a systematic study of the evolution of the densest regions of the Universe, as traced by the most massive galaxies and their environments, improving our understanding of how the most massive regions of the Universe form and evolve. This will only be possible by using data from a deep mid-infrared wide-field survey, the Spitzer Extragalactic Representative Volume Survey (SERVS), which has just finished the data processing for a 1400 hour-long observational programme capable of finally overcoming long-standing observational limitations. In this thesis, the student will: a) use the deep radio surveys of these fields, already performed either at 1.4 GHz (VLA) or 610 MHz (GMRT), or both; b) identify High-redshift Radio Galaxies in these fields. This will be possible either by studying Ultra Steep (Radio) Spectrum sources, candidates for such objects (when radio observations exist at more than one frequency), or by directly estimating radio luminosities of radio sources using the existent spectroscopic or newly obtained accurate photometric redshifts. The wide area nature of SERVS, covering 18 deg2 of the sky (or 0.8 Gpc3 over 110^13 Msun) dark matter haloes will be contained in this volume. Many will have a massive galaxy in its core, and many of these should be very luminous at radio wavelengths; c) identify companion galaxies to the radio galaxies, thus tracing the environments of the most massive galaxies. Identification of candidates will be performed on the basis of projected distance in the infrared data, and photometric or spectroscopic redshifts will then be used to confirm the physical connection to the Radio Galaxy. The sensitivity of SERVS is enough to detect galaxies with characteristic luminosity (L*) to z~5, which will allow a detailed census of the vicinity of the Radio Galaxy to be performed; d) characterize the environments of these massive radio galaxies, by measuring density of companion galaxies, and their properties: obscured and unobscured star-formation and AGN activity, stellar masses, star-formation ages. This will provide a comprehensive characterization (current state and history) of the environments of massive Radio Galaxies, which will be tracing the most massive dark matter haloes. By using SERVS data we will be able to cover rest-frame near-IR emission from our selected galaxies, sampling light from both old stellar populations and younger AGB stars. Together with improved stellar population synthesis models, this will allow for a reliable determination of galaxy ages and masses, robust against degeneracies; e) map the evolution of clustering properties in massive dark matter haloes over a significant fraction of the Universe’s history, and compare with predictions from hierarchical structure formation models. This will result in a fundamental test for such models, and will reveal how they should be improved to better explain the formation and evolution of large scale structure in the Universe.