Most of the cool CGM of star-forming galaxies is not produced by supernova feedback

TL;DR

This study shows that supernova feedback is unlikely to be the main driver of cool gas in galaxy halos, suggesting cosmological inflows are more responsible for the observed circumgalactic medium around star-forming galaxies.

Contribution

The paper introduces semi-analytical models and Bayesian analysis to test supernova-driven outflows against observational data, challenging previous assumptions about CGM origins.

Findings

Supernova-driven outflows cannot explain the observed cool CGM dynamics.

Extreme model parameters are required for supernova feedback to match observations, which are physically implausible.

Most cool CGM gas likely results from cosmological inflows rather than supernova feedback.

Abstract

The characterization of the large amount of gas residing in the galaxy halos, the so called circumgalactic medium (CGM), is crucial to understand galaxy evolution across cosmic time. We focus here on the the cool ($T\sim10^4$ K) phase of this medium around star-forming galaxies in the local universe, whose properties and dynamics are poorly understood. We developed semi-analytical parametric models to describe the cool CGM as an outflow of gas clouds from the central galaxy, as a result of supernova explosions in the disc (galactic wind). The cloud motion is driven by the galaxy gravitational pull and by the interactions with the hot ($T\sim10^6$ K) coronal gas. Through a bayesian analysis, we compare the predictions of our models with the data of the COS-Halos and COS-GASS surveys, which provide accurate kinematic information of the cool CGM around more than 40 low-redshift star-forming galaxies, probing distances up to the galaxy virial radii. Our findings clearly show that a supernova-driven outflow model is not suitable to describe the dynamics of the cool circumgalactic gas. Indeed, to reproduce the data, we need extreme scenarios, with initial outflow velocities and mass loading factors that would lead to unphysically high energy coupling from the supernovae to the gas and with supernova efficiencies largely exceeding unity. This strongly suggests that, since the outflows cannot reproduce most of the cool gas absorbers, the latter are likely the result of cosmological inflow in the outer galaxy halos, in analogy to what we have previously found for early-type galaxies.