Research | GulayGurkan

Active Galactic Nuclei

(AGN)

AGN are important in galaxy evolution because the interactions between supermassive black holes and their host galaxies (AGN feedback: jets and/or radiative output), as suggested by theoretical studies, regulate or quench star formation in galaxies.

I carried out statistical sample studies and investigated the accretion modes in AGN which are very bright at radio wavelengths (i.e. radio-loud AGN) using mid-IR data and showed that mid-IR colour classifications of AGN should be used with a caution. I compared star formation properties of radio-loud and radio-quiet AGN in the Local Universe which showed that there is tentative evidence for the AGN -SFR link for both AGN classes but radio-quiet AGN exhibit higher SFR than their RL counterparts. I also focused on optically bright AGN (i.e. quasars) using highly sensitive radio data. This study demonstrated that optically selected quasars have a wide range of radio properties.

Extragalactic

star formation

Star formation derives galaxy evolution. There are various indicators that can be used to infer star formation rates (SFRs) of galaxies. Common SFR tracers, like UV/optical emission from stars, are heavily obscured by intervening dust, whereas radio waves can penetrate dust which makes them to be the ideal star formation tracer.

I probed the relationship between low-frequency radio luminosity and SFR in local star-forming galaxies and showed that low frequency radio emission traces SFR, with a clear dependence on galaxy mass. Additionally, this study showed that low-luminosity AGN in the Local Universe is a potential contaminating population.

Wide-field

radio surveys

Wide-area, sensitive radio surveys, in conjunction with wide-area optical photometric and spectroscopic surveys provide us with the ideal way to study various processes in a statistical way in the Universe. Wide-area surveys are required in order to find statistically meaningful samples of AGN and star-forming galaxies as well as discover the unknown.

I have been involved in a number of wide-field radio surveys such as the Low Frequency Radio Array Two-Metre Sy Survey (LoTSS), The Australian SKA Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey, deeper LOFAR surveys over specific regions, the Polarization Sky Survey of the Universe's Magnetism (POSSUM), and the Murchison Wide-field Array-based surveys.