CO Spectral Line Energy Distributions of IR-luminous galaxies and AGN

TL;DR

This study presents new high-J CO line observations of luminous infrared galaxies and AGN, constructing local CO SLEDs to better understand the properties of star-forming molecular gas without high-redshift biases.

Contribution

It provides the first local CO SLEDs for global molecular gas reservoirs, combining new JCMT data with existing observations to improve understanding of star formation in IR-luminous galaxies.

Findings

CO SLEDs extend to high J-levels, revealing excitation conditions.

Local CO SLEDs are unbiased by lensing or undersampling.

Results improve understanding of molecular gas properties in IR-luminous galaxies.

Abstract

We report on new sensitive CO J=6-5 line observations of several luminous infrared Galaxies (LIRGs: L$_{\rm IR}$(8-1000$\mu $m$)\ga 10^{11}$ L$_{\odot}$), 36% (8/22) of them ULIRGs (L$_{\rm IR}$$>10^{12}$ L$_{\odot}$), and two powerful local AGN: the optically luminous QSO PG 1119+120, and the powerful radio galaxy 3C 293 using the James Clerk Maxwell Telescope (JCMT) on Mauna Kea in Hawaii. We combine these observations with existing low-J CO data and dust emission Spectral Energy Distributions (SEDs) in the far-infrared - submillimetre from the literature to constrain the properties of the star-forming ISM in these systems. We then build the first {\it local} CO Spectral Line Energy Distributions (SLEDs) for the {\it global} molecular gas reservoirs that reach up to high J-levels. These CO SLEDs are neither biased by strong lensing (which affects many of those constructed for high-redshift galaxies), nor suffer from undersampling of CO-bright regions (as most current high-J CO observations of nearby extended systems do). We find: ...