(Sub)millimetre-selected galaxies and the cosmic star-formation history

Abstract

Understanding the time evolution of the star formation in the Universe is one of the main aims of observational astronomy. Since a significant portion of the UV starlight is being absorbed by dust and re-emitted in the IR, we need to understand both of those regimes to properly describe the cosmic star formation history. In UV, the depth and the resolution of the data permits calculations of the star formation rate densities out to very high redshifts (z ∼ 8 − 9). In IR however, the large beam sizes and the relatively shallow data limits these calculations to z ∼ 2. In this thesis, I explore the SMA and PdBI high-resolution follow-up of 30 bright sources originally selected by AzTEC and LABOCA instruments at 1.1 mm and 870 μm respectively in conjunction with the SCUBA-2 Cosmology Legacy Survey (S2CLS) deep COSMOS and wide UDS maps, where 106 and 283 sources were detected, with the signal-to-noise ratio of > 5 and > 3.5 at 850 μm respectively. I find that the (sub)mm-selected galaxies reside and the mean redshifts of ¯z ≃ 2.5±0.05 with the exception of the brightest sources which seem to lie at higher redshifts (¯z ≃ 3.5 ± 0.2), most likely due to the apparent correlation of the (sub)mm flux with redshift, where brighter sources tend to lie at higher redshifts. Stellar masses, M⋆, and star formation rates, SFRs, were found (M⋆ & 1010M⊙ and SFR & 100M⊙ yr−1) and used to calculate the specific SFRs. I determine that the (sub)mm-selected sources mostly lie on the high-mass end of the star formation ‘main-sequence’ which makes them a high-mass extension of normal star forming galaxies. I also find that the specific SFR slightly evolves at redshifts 2−4, suggesting that the efficiency of the star formation seems to be increasing at these redshifts. Using the S2CLS data, the bolometric IR luminosity functions (IR LFs) were found for a range of redshifts z = 1.2 − 4.2 and the contribution of the SMGs to the total star formation rate density (SFRD) was calculated. The IR LFs were found to evolve out to redshift ∼ 2.5. The star formation activity in the Universe was found to peak at z ≃ 2 followed by a slight decline. Assuming the IR to total SFRD correction found in the literature the SFRD found in this work closely follows the best-fitting function of Madau & Dickinson (2014).