The Intergalactic Medium

The temperature-density relation of baryonic matter at the present cosmic time, as obtained from numerical simulations (Gaikwad et al 2017). The points leftward of the vertical dashed line correspond to low-density gas, i.e., the intergalactic medium (IGM), while those to the right of the line correspond to baryons within galaxies. The IGM consists of a warm-hot phase (labelled "WHIM") and a cold phase (labelled "Diffuse").

(Tirthankar Roy Choudhury, Nissim Kanekar, Former members: Prakash Gaikwad, Vikram Khaire)

The intergalactic medium (IGM) is the low-density diffuse gas spread in between galaxies. In fact, most of the matter (both ordinary baryons and dark matter) in the universe lies in the IGM. The gas in the IGM provides "raw material" for the formation of galaxies at early cosmic times. On the other hand, matter and energy from galaxies can be ejected into the IGM because of outflows. As a result, the IGM is imprinted with information on cosmological initial conditions and astrophysical processes related to galaxy formation.

Scientists at NCRA-TIFR are involved in analysing different kinds of observational data related to the IGM, mostly at optical and ultra-violet bands, to understand the high-redshift Universe. This is complemented by detailed modelling using state-of-the-art numerical simulations which can help understand the physical conditions of the IGM and the properties of galaxies at different cosmic times.