Extragalactic Astronomy

1. IGM: Most of the bayrons created in the Big bang reside in regions between galaxies. These regions are called Intergalactic medium (IGM).  Absorption lines imprinted in the spectra of distant bright objects such as quasars or Gamma ray bursts allow us to probe the physics of the IGM and its redshift evolution. In particular the astronomers at IUCAA have made important contributions to this field such as: (1) Measuring the HI photoionization rate as at low-z, (2) Computing consistent UV background as a function of redshift, (3) Constraining the UV escape fraction from star forming galaxies, (4) Accurately measuring the thermal evolution of the IGM that allow one to probe the physical condition during He II reionization, (5) First measurement of redshift space three-point correlation function at low-z, (6) Accurate measurement of redshift evolution of two- and three-point correlation function  (7) large survey of OVI at high-z (8) accurate modeling of metal line absorbers and (9) heating of the IGM using cosmic rays. At present the team is involved in the hydrodynamical modeling of the IGM using Gadget 3.
   
   
2. Quasar absorption lines - Galaxy evolution and Cosmology: Strong absorption lines seen in spectra of high-z quasars allow us to probe cosmology, fundamental physics and galaxy evolution. IUCAA astronomers measure the temperature of the cosmic microwave background at different redshifts to confirm the big-bang model. The team also provided one of the most stringent measurements on the time variation of electromagnetic coupling constant and electron-to-proton mass ratio using quasar absorption lines.
   
   Detection of HI 21-cm absorption and or molecular species at high-z allow one to probe the physical state of the interstellar medium in protogalaxies. IUCAA astronomers (and their collaborators) have carried out different surveys using GMRT and VLT to build the largest sample of such absorbers. Some IUCAA faculty members are now carrying out one of the largest surveys (MeerKAT Absorption Line Survey, MALS) to detect HI 21cm and OH absorption over the redshift range 0<z<2.
   
   Establishing the connection between the absorption lines seen in the spectrum of quasars and their host galaxies are very important to understand the galaxy evolution in a luminosity unbiased way. Several students in IUCAA are involved in such an activity using large telescopes and most advanced instruments such as MUSE.
   
   
3. Galaxy evolution: Galaxies, primarily made up of stars, gas and invisible dark matter, are the fundamental building blocks of our universe. When and how these galaxies have formed remain as one of the outstanding challenges in modern astronomy. The challenges arise because galaxies are not isolated systems like “Island universes”; they are highly interacting, they merge with another, accrete gas/satellites from surrounding or the cosmic web, they also pollute the intergalactic medium by ejecting materials outwards. But when one inspects a galaxy at a given redshift slice or say in the local universe (already about 13.7 billion years old), several of these factors may get erased due to the dynamics of stars or hard to disentangle. 
   
   At IUCAA, galaxy research ranges from high-redshift, young, star-forming galaxies to the local, matured ones like our Milky Way. Researchers use state-of-the-art N-body simulation carried out at IUCAA HPC to understand their dynamical evolution. They also use multi-wavelength data from various large ground-based surveys like SDSS; deep surveys from space-based telescopes like HST, Spitzer and now AstroSat’s UVIT for far and near-UV observations as well as Integral Field Spectroscopic data from surveys like MANGA to address the above mentioned challenges.