CO luminosity function from Herschel-selected galaxies and the contribution of AGN

TL;DR

This paper derives the CO luminosity function from Herschel-selected galaxies across multiple redshifts, compares it with models, and assesses the role of luminous AGN in shaping the bright end at z≈2.

Contribution

It presents a new derivation of the CO luminosity function using Herschel data and evaluates the impact of AGN on the bright end at high redshift.

Findings

Predicted CO LFs match observed data at z≈0 and 2.

Good agreement with semi-analytical models at z≈0.

Luminous AGN are too rare to explain the bright end at z≈2.

Abstract

We derive the CO luminosity function (LF) for different rotational transitions (i.e. (1-0), (3-2), (5-4)) starting from the Herschel LF by Gruppioni et al. and using appropriate $L'_{\rm CO} - L_{\rm IR}$ conversions for different galaxy classes. Our predicted LFs fit the data so far available at $z\approx0$ and $2$. We compare our results with those obtained by semi-analytical models (SAMs): while we find a good agreement over the whole range of luminosities at $z\approx0$, at $z\approx1$ and $z\approx2$ the tension between our LFs and SAMs in the faint and bright ends increases. We finally discuss the contribution of luminous AGN ($L_{X}>10^{44}\,\rm{erg\,s^{-1}}$) to the bright end of the CO LF concluding that they are too rare to reproduce the actual CO luminosity function at $z\approx2$.