# Cooling lines as probes of the formation and buildup of galaxies and black holes

## TL;DR

This paper explores how SPICA's cooling line observations, especially high-J CO lines, can distinguish star formation from black hole activity across cosmic history, including primordial galaxies.

## Contribution

It introduces the use of high-J CO cooling lines as a diagnostic tool for separating star formation and AGN activity in galaxies, including at high redshift.

## Key findings

- High-J CO lines effectively differentiate star formation from AGN activity.
- SPICA can detect cooling radiation from primordial, low-metallicity galaxies.
- Review of current efforts on high-J CO emission studies at various redshifts.

## Abstract

We discuss the use of SPICA to study the cosmic history of star formation and accretion by supermassive black holes. The cooling lines, in particular the high-J rotational lines of CO, provide a clear-cut and unique diagnostic for separating the contributions of star formation and AGN accretion to the total infrared luminosity of active, gas-rich galaxies. We briefly review existing efforts for studying high-J CO emission from galaxies at low and high redshift. We finally comment on the detectability of cooling radiation from primordial (very low metallicity) galaxies containing an accreting supermassive black hole with SPICA/SAFARI.