# ALMA observations of cold molecular gas in AGN hosts at z~1.5 - Evidence of AGN feedback?

## TL;DR

This study uses ALMA to observe molecular gas in AGN host galaxies at z~1.5, providing evidence that AGN feedback may reduce gas content and star formation efficiency during this cosmic epoch.

## Contribution

First direct comparison of molecular gas in AGN and non-AGN galaxies at z~1.5, showing potential AGN feedback effects on gas depletion and star formation.

## Key findings

- AGN hosts show lower molecular gas fractions.
- AGN hosts have shorter gas depletion times.
- Evidence suggests AGN feedback influences star formation efficiency.

## Abstract

Similarly to the cosmic star formation history, the black hole accretion rate density of the Universe peaked at 1<z<3. This cosmic epoch is hence best suited for investigating the effects of radiative feedback from AGN. Observational efforts are underway to quantify the impact of AGN feedback, if any, on their host galaxies. Here we present a study of the molecular gas content of AGN hosts at z~1.5 using CO[2-1] line emission observed with ALMA for a sample of 10 AGNs. We compare this with a sample of galaxies without an AGN matched in redshift, stellar mass, and star formation rate. We detect CO in 3 AGNs with $\mathrm{L_{CO} \sim 6.3-25.1\times 10^{9} L_{\odot}}$ which translates to a molecular hydrogen gas mass of $\mathrm{2.5-10\times 10^{10} M_{\odot}}$ assuming conventional conversion factor of $\mathrm{\alpha_{CO}}\sim3.6$. Our results indicate a >99% probability of lower depletion time scales and lower molecular gas fractions in AGN hosts with respect to the non-AGN comparison sample. We discuss the implications of these observations on the impact that AGN feedback may have on star formation efficiency of z>1 galaxies.