# Extreme submillimetre starburst galaxies

## TL;DR

This paper investigates extreme starburst galaxies at high redshift using Herschel and IRAS data, revealing their star-formation rates, gas content, and active galactic nucleus characteristics, and discusses their role in galaxy evolution.

## Contribution

The study provides new insights into the properties of extreme starburst galaxies at redshifts 3-5, including their star-formation rates, gas masses, and AGN activity, based on combined Herschel and IRAS data.

## Key findings

- Star-formation rates exceed 5000 Msun/yr, with a maximum around 30,000 Msun/yr.
- Over 50% of these galaxies show evidence of AGN activity in their SEDs.
- Galaxies at z=3-5 have gas masses comparable to their stellar masses.

## Abstract

We use two catalogues, a Herschel catalogue selected at 500 mu (HerMES) and an IRAS catalogue selected at 60 mu (RIFSCz), to contrast the sky at these two wavelengths. Both surveys demonstrate the existence of extreme starbursts, with star-formation rates (SFRs) > 5000 Msun/yr. The maximum intrinsic star-formation rate appears to be ~30,000 Msun/yr. The sources with apparent SFR estimates higher than this are in all cases either lensed systems, blazars, or erroneous photometric redshifts. At redshifts of 3 to 5, the time-scale for the Herschel galaxies to make their current mass of stars at their present rate of formation ~ 10^8 yrs, so these galaxies are making a significant fraction of their stars in the current star-formation episode. Using dust mass as a proxy for gas mass, the Herschel galaxies at redshift 3 to 5 have gas masses comparable to their mass in stars. Of the 38 extreme starbursts in our Herschel survey for which we have more complete SED information, over 50% show evidence for QSO-like optical emission, or exhibit AGN dust tori in the mid-infrared SEDs. In all cases however the infrared luminosity is dominated by a starburst component. We derive a mean covering factor for AGN dust as a function of redshift and derive black hole masses and black hole accretion rates. There is a universal ratio of black-hole mass to stellar mass, ~ 10^{-3}, driven by the strong period of star-formation and black-hole growth at z = 1-5.