Ia Kochiashvili PhD Thesis Defense

Ia Kochiashvili will defend her PhD thesis on May 11, 1:30 PM, in the DARK Lounge.

Title: High redshift Lyman- hunt – Galaxies as precious forged jewels
Supervisor:  Johan Fynbo, Dark Cosmology Centre
PhD Committee:  Anja C. Andersen, Dark Cosmology Centre (Chair)
Opponents:  Páll Jakobsson, Professor, Univ. of Iceland
                    Simona Mei, Professor, Observatoire de Paris

Abstract: Galaxy formation and evolution has been intensively studied in the past two decades. Results and discoveries revolutionized the field and we now have much better understanding of how these huge conglomerates of baryonic and dark matter evolve.

In the framework of two different projects, which constitute the backbone of this thesis, I investigated the nature of almost 100 emission-line galaxies selected with the narrow-band selection method. These candidates can be: galaxies with Hα emission lines at redshift z~0.6, [O III]/Hβ emission-line galaxies at redshift z~1.15 and [O II] emitters at z~1.85.

I used the near-infrared data from NB1060, Y and J filters to perform colour-colour and colour-magnitude selections. With the broad-band data from CANDELS catalogue, I performed SED fitting and derived photometric redshifts and other physical properties for the candidate emission-line galaxies. Significant differences between the two selection methods have been found. The colour-colour selection method tends to pick galaxies with high colour excess and can leave some strong emission-line candidates with relatively lower colour excess out of the sample. The populations of selected galaxies can also be very biased. The colour-magnitude selection method picks not only ``normal'' galaxies, but also starburst ones.

I investigated the physical properties and colour indices for the selected galaxies, obtaining the following results.

I). Stellar masses for narrow-band selected galaxies are found to be in the range M*~10⁷-10¹¹ M_¤. The derived star-formation rates suggest that they can be either normal galaxies in the main sequence of the M* vs. SFR relation, or starburst ones. II). A steepening of the M* vs. SFR slope for the galaxies in the lower part of the mass range (M*<10^9.4M_¤) is found. III). From studying the spatial distribution of our sample the discovery of a galaxy protocluster at the redshift of z=1.85 and the likely discovery of a filament at z=1.15 are reported. The identification of these gravitationally bound structures holds regardless of selection method employed in the analysis.

In this thesis, I also briefly summarise the first results of an on-going investigation of galaxies selected according to their robust spectroscopic redshifts from the large MUSYC multiband survey. The aim of this project is to study the evolution of the physical properties of galaxies across large redshift range (0<z<6) and see their implications on the evolution of the universe.

Link to thesis here >>