Astrophysics Vacation Research Experience Scheme (VRES) of 2024. Investigation of AGN contamination on UVJ colour-colour diagram
The contamination of AGN (Active Galactic Nucleus) emissions is believed to be a significant issue in astronomy due to the effects they cause in the measure- ments and analysis of studies concerning AGN host galaxies. The accretion of dust by a supermassive black hole creates an AGN in the center of a galaxy. We investigate the contamination of an AGN host galaxy to the restframe UVJ diagram (U-V versus V-J), a tool used to classify galaxy types (Star-forming, Quiescent and dusty) based on their dominant colours as detected by differ- ent photometric bands used. The data utilised in the research are photometric data collected using the Magellan telescope by the FourStar Galaxy Evolution Survey (ZFOURGE) in the COSMOS legacy field. First, the high-quality sam- ple is selected from the large data of ZFOURGE. Then AGN host galaxies are distinguished from non-AGN in the large survey data by the passing criteria: mass-complete (log(M∗/M⊙)) ≥ 10, and only galaxies of the redshift 1 ≤ z < 4 are considered. The AGN host galaxy data are further analysed by Code Inves- tigating GALaxy Emission (CIGALE) software which by comparing modeled galaxy Spectral Energy Distributions (SEDs) provides more data on the AGN luminosity of 1,000 galaxies from the sample. We plot multiple restframe UVJ colour-colour diagrams which differ by specific redshifts, stellar masses, and AGN luminosity. Though it is preconceived for an AGN host galaxy to affect on UVJ diagram, We find negligible to no differences driven by the AGN host galaxy contamination on the UVJ diagram compared to the rest of the galaxies. Additionally, the majority of AGN host galaxies fall between a redshift of 1.6 to 2.2 which supports the phenomenon known as ”Cosmic Noon” that happened in the early universe. However, we find no evidence of cosmic noon causing any AGN contamination.