# PAH emission and star formation in the host of the z~2.56 Cloverleaf QSO

## TL;DR

This study detects PAH emission features in a high-redshift QSO, indicating that its large infrared luminosity is mainly due to starburst activity coinciding with active quasar phases.

## Contribution

First detection of PAH features in a z~2.56 QSO, linking star formation and quasar activity in the early universe.

## Key findings

- PAH features similar to local star-forming galaxies
- Star formation rate around 1000 solar masses per year
- Gas exhaustion time approximately 30 million years

## Abstract

We report the first detection of the 6.2micron and 7.7micron infrared `PAH' emission features in the spectrum of a high redshift QSO, from the Spitzer-IRS spectrum of the Cloverleaf lensed QSO (H1413+117, z~2.56). The ratio of PAH features and rest frame far-infrared emission is the same as in lower luminosity star forming ultraluminous infrared galaxies and in local PG QSOs, supporting a predominantly starburst nature of the Cloverleaf's huge far-infrared luminosity (5.4E12 Lsun, corrected for lensing). The Cloverleaf's period of dominant QSO activity (Lbol ~ 7E13 Lsun) is coincident with an intense (star formation rate ~1000 Msun/yr) and short (gas exhaustion time ~3E7yr) star forming event.