Thesis

Diffuse ionized gas and Lyman continuum photon escape in spiral galaxies

• Call:

  IDPASC Portugal - PHD Programme 2019

• Academic Year:

  2019 / 2020

• Domain:

  Astrophysics

• Supervisor:

  Polychronis Papaderos

• Co-Supervisor:

  Jean Michel Gomes

• Institution:

  Universidade do Porto

• Host Institution:

  Instituto de Astrofísica e Ciências do Espaço, Centro de Astrofísica da Universidade do Porto

• Abstract:

  Diffuse ionized gas (DIG) is an ubiquitous component in the disk and halo of late-type galaxies (LTGs). The excitation mechanisms and ionization conditions of the DIG pose a long-standing enigma. The prevailing picture though is that the DIG originates from Lyman continuum (LyC) photons escaping from sites of ongoing star formation and their reprocessing into nebular emission on scales of ~1 kpc away from HII regions. The mechanisms facilitating escape and transport of LyC radiation are unclear, it is yet likely that a key role is played by injection of energy and momentum by stellar winds and SNe into a porous multi-phase interstellar medium. Various lines of evidence indicate that the diffuse, low-surface brightness DIG contributes ~20-50% of the total Hα emission in late-type galaxies, a fact that may introduce a substantial observational bias on estimates of star formation rates in high-redshift galaxies where DIG emission is barely detectable. This project aims at a detailed investigation of the physical properties of the DIG in a representative sample of nearby face-on spiral galaxies using image processing techniques, spatially resolved integral field spectroscopy and advanced spectral synthesis models. A central question to be addressed concerns the relation between the fractional contribution of the DIG to the total Hα luminosity and the star formation history and structural properties of LTGs.