Cosmology

Cosmology is the study of the evolutionary history of our Universe. Cosmology can be best described pictographically by the famous Paul Gauguin's 1897 painting, Where do we come from? What are we? Where are we going?.

The present age is the era of Precision Cosmology, which is driven by large-scale surveys of the Universe conducted via Earth-based and space-based telescopes/experiments operating across the electromagnetic spectrum. Starting from radio (GMRT, MWA, LOFAR, MeerKAT, SKA etc.), infrared (TIM, CONCERTO, COMAP, SPHEREx etc.), microwave (Planck, WMAP etc.), optical (Hubble, JWST, LSST, TMT, ELT, SDSS, DES etc.), X-ray (eROSITA) wavelengths and also including the gravitational waves (LIGO).  

Many members of DAASE are actively involved in the national and international research teams of the above-mentioned experiments in cosmology. 

• These multiwavelength surveys help us to probe the evolving state of the Universe, starting from the time when the matter and radiation got decoupled from each other and Cosmic Microwave Background Radiation was released, to the age of formation of first stars (Cosmic Dawn), to the stage when the intergalactic medium went through a phase change -- from neutral to ionized (Epoch of Reionization), to the present day when we observe the galaxies to be distributed around us in the form of a complex cosmic web at very large scales. 

• Multiwavelength Line Intensity Mapping is one of the most powerful tools to probe the Universe at large scales across cosmic time. In this method, a redshifted atomic or molecular line is targeted to map out the Universe. These lines arise due to different physical processes that take place in the intergalactic medium and in the interstellar medium. One such atomic line is the 21-cm line (rest frame wavelength) emitted by the spin-flip transition in the neutral hydrogen atoms (HI), the most abundant baryon in our Universe.  The cosmologically redshifted 21-cm line, observed via radio telescopes, allows us to probe the state of the intergalactic medium and the nature of the first luminous sources, starting from the Cosmic Dark Ages to the Epoch of Reionization. Once the reionization of the Universe is complete, the same line then maps the neutral hydrogen trapped in the galaxies, thus probing the large-scale structures. Similarly, other atomic and molecular lines e.g. singly ionized carbon (CII), carbon monoxide (CO), doubly ionized oxygen (OIII), observed via infrared telescopes, are used to map the star-forming galaxies in the Universe from the Cosmic Dawn to the present day. 

• These multiwavelength surveys help us address many fundamental questions in cosmology, e.g. what are the major constituents of our Universe, what is the nature of the dark matter and dark energy, how were the first galaxies formed, how did they affect the state of the intergalactic medium and also the subsequent galaxy formation, how did the galaxies arranged themselves in the complex cosmic web that we see around us today.  

• Galaxy clusters are the largest gravitationally bound structures in the Universe. Multiwavelength (mostly X-ray and radio) observations of the galaxy clusters can reveal the nature of the dark matter and help us to verify the standard models of cosmology.

• Large-scale Numerical Simulations of the Universe, starting from the early stages of the Universe to the present day, Advanced Machine Learning algorithms for emulation of the cosmological signals and robust Bayesian inference frameworks help us in interpreting these complex observations and reveal the mysterious nature of the Universe. 

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