Simulated [CII] in high-z galaxies

TL;DR

This study uses a post-processing model on Illustris-TNG50 simulations to analyze [CII] emission in high-redshift galaxies, comparing results with ALPINE observations and exploring the origins of extended [CII] halos.

Contribution

It introduces a new post-processing approach to simulate [CII] emission in high-z galaxies and compares these with observations, highlighting discrepancies and potential origins of extended emission.

Findings

Model reproduces galactic-scale [CII] emission similar to observations.

Predicted [CII] in the inner CGM is about 10 times lower than observed.

Extended [CII] emission likely arises from satellite gas and outflows, with satellites being dominant.

Abstract

Extended [CII] emission on tens of kpc, also known as a [CII] halo, is being currently reported around z$\sim$4-6 star-forming galaxies, especially thanks to the statistics of the ALPINE survey. The [CII] emission is expected to trace dense cold gas in the inner CGM of these galaxies. The origin of this emission is still debated. In this paper, we present a post-processing model applied to Illustris-TNG50 star-forming galaxies at $z\sim$4-6, and we compare our results with the ALPINE observations. By incorporating C$^{+}$ abundances derived from UV background and young stars as radiation sources, we generate mock observations, from which we extract surface-brightness (SB) profiles. We found that our model predicts similar [CII] emission values on galactic scales as the observations, providing validation for our approach. However, we find that the predicted [CII] emission in the inner circumgalactic medium (CGM) falls below the observed values by a factor of $\sim$10. We discuss several model limitations that may contribute to this discrepancy. We also find discrepancies with observations when comparing SB profiles of low and high-SFR galaxies. Unlike the observations, simulations exhibit no discernible difference in the extended [CII] emission between the two subsamples. This discrepancy may reflect shortcomings in feedback model of the simulation. Finally, our analysis suggests that the extended [CII] emission is likely a result of both gas from satellite galaxies and outflows from central galaxies, with satellites playing a dominant role within 0.6$<$R/R$_{\rm vir}<$1. A firm estimate of the importance of each contribution is beyond the scope of the current simulations.