About

Several models have been developed and studied to explain the current state of our universe. Unravelling the true mechanism behind galaxy formation and evolution will hugely impact our understanding of the present universe and is therefore, of great significance to Astronomy. To handle the overwhelming amount of data required to construct a complete evolutionary picture, an efficient technique of interpretation and analysis isrequired (like in Reddy et al., 2015). This project uses the method of studying emission properties of the galaxy population as a whole. It involves tracing the evolution of the galaxy luminosity density from the far-UV (FUV) to the far-infrared (FIR) with cosmic time. This gives a way to empirically resolve the global history of star formation in the Universe, autonomous of the complex evolutionary phases of the individual galaxy sub-populations. For the stated purpose, dust attenuation and different dust production mechanisms are briefly explored. An attempt to examine the findings of R. Maiolino et al. (2004) is made by taking a sample of 105 high redshift galaxies. In particular, these findings pointed towards a supernova origin for dust in a high- redshift quasar, which suggested the same could apply to galaxies at high redshifts. Exploring this tests the speculation that dust attenuation curves look different for the first generations of galaxies than at later times due to different dust production mechanisms. Recent spectroscopic redshift measurements together with extensive multiwavelength datasets are inspected to reconstruct the dust attenuation curve of z=4-6 galaxies, in other words to inspect galaxies within ~0.9-1.5 Gyr of cosmic history. These attenuation curves and obtained physical quantities, in turn, are used to see how the high redshift galaxies of our sample compare with the local universe galaxies. The goal is to model and fit the spectral energy distributions of star-forming galaxies using Code Investigating GALaxy Emission (CIGALE) to gain a detailed understanding of how dust affects the properties. The techniques to perform the analysis are reviewed, along with developing understanding of dust formation and its influence on galaxy spectra. to gain a detailed understanding of how dust affects the properties.

Results

The data is analyzed, results are interpreted and here the conclusions are briefly listed with the future scope of the project. The analysis suggests that the physical properties of galaxies are highly influenced by dust and this influence, in particular the preferential absorption of ultraviolet light which is reemitted in the IR, helps configure the dust properties and model attenuation curves. The attenuation curves are reconstructed using the slope of the attenuation curve, δ, obtained from CIGALE. Analysis of the physical quantities derived using SED modelling and fitting for galaxies sheds light on the dust properties. The IRX-beta plots suggest that the early universe galaxies fairly follow the starburst (Meurer) relation. There is roughly an overall trend that redder UV slopes correspond to higher IRX values. It can be said that even though galaxies of a particular type identify with their own IRX-β relations on a very precise level, the overall galaxy population presents a complicated picture. For the redshifts range studied in this project though, for both subsets and in both models, galaxies fairly comply with the Meurer relation with observable yet admissible scatter. With improved measurements and analysis in multi-wavelength datasets, the estimation of dust content from techniques like the IRX-β relation will probably yield more robust techniques. The attenuation curve reconstructed here gives two main observations: its slope in the UV/optical wavelength range and the absence of additional absorption at the near-UV, known as the UV bump. Since CIGALE allows for deviation of the slope from the slope of the Calzetti curve, attenuation curves both steeper than Calzetti curve and shallower than the Calzetti curve are obtained. The attenuation curves of our sample are more similar to the Calzetti curve than SMC (with δ ~ -0.45) for quite a few galaxies. The work also indicates that both attenuation laws – modified Calzetti and Charlot and Fall - model and fit the SEDs almost equally well, even with a key difference in their power laws. The Charlot and Fall model shows a higher correlation overall than the Calzetti model, neither of the observations being debatably far apart. Lastly, the work in projects like this can be further complimented by conducting a more comprehensive analysis that involves a more detailed modelling of physical properties and their interplay. Future observations with JWST and further growing observations in the millimeter/submillimeter by ALMA too has the scope to derive an accurate and more complete picture of galaxy evolution and cosmic star formation, as better observations can test existing theoretical models and pave way for improved empirical ones