Resolving small-scale cold circumgalactic gas in TNG50

Understand

We use the high-resolution TNG50 cosmological magnetohydrodynamical simulation to explore the properties and origin of cold circumgalactic medium (CGM) gas around massive galaxies (M* > 10^11 Msun) at intermediate redshift (z~0.5).

• We discover a significant abundance of small-scale, cold gas structure in the CGM of 'red and dead' elliptical systems, as traced by neutral HI and MgII.
• Halos can host tens of thousands of discrete absorbing cloudlets, with sizes of order a kpc or smaller.
• With a Lagrangian tracer analysis, we show that cold clouds form due to strong drho/rho >> 1 gas density perturbations which stimulate thermal instability.