# Cool circumgalactic gas of passive galaxies from cosmological inflow

## TL;DR

This paper models the cool circumgalactic gas around passive early-type galaxies as cosmological inflow of clouds, explaining observed properties and why these galaxies are quiescent.

## Contribution

It introduces a semi-analytical inflow model that successfully reproduces observed cool gas properties around passive galaxies, highlighting cloud evaporation as a key process.

## Key findings

- Inflow models match observed cool gas kinematics and column densities.
- Cool clouds have masses around 10^5 solar masses and evaporate before reaching galaxy centers.
- Cool gas likely does not feed star formation in passive galaxies.

## Abstract

The circumgalactic medium (CGM) of galaxies consists of a multiphase gas with components at very different temperatures, from $10^ {4}$ K to $10^ {7}$ K. One of the greatest puzzle about this medium is the presence of a large amount of low-temperature ($T\sim10^4$ K) gas around quiescent early-type galaxies (ETGs). Using semi-analytical parametric models, we describe the cool CGM around massive, low-redshift ETGs as the cosmological accretion of gas into their dark matter halos, resulting in an inflow of clouds from the external parts of the halos to the central galaxies. We compare our predictions with the observations of the COS-LRG collaboration. We find that inflow models can successfully reproduce the observed kinematics, the number of absorbers and the column densities of the cool gas. Our MCMC fit returns masses of the cool clouds of about $10^5\ \rm{M}_{\odot}$ and shows that they must evaporate during their journey due to hydrodynamic interactions with the hot gas. We conclude that the cool gas present in the halos of ETGs likely cannot reach the central regions and feed the galaxy star formation, thus explaining why these passive objects are no longer forming stars.