# A survey of molecular gas in luminous sub-millimetre galaxies

**Authors:** M. S. Bothwell, Ian Smail, S. C. Chapman, R. Genzel, R. J. Ivison, L. J. Tacconi, S. Alaghband-Zadeh, F. Bertoldi, A. W. Blain, C. M. Casey, P. Cox, T. R. Greve, D. Lutz, R. Neri, A. Omont, A. M. Swinbank  
**arXiv:** [1205.1511](https://arxiv.org/abs/1205.1511)  
**Date:** 2012-05-07  
**Summary page:** https://www.summarizepaper.com/en/paper/1205.1511v1/

## Key points

- Results of comprehensive survey on 12CO emission in luminous sub-millimetre galaxies (SMGs)
- Detection of 12CO emission in 32 SMGs at redshifts between z~1.2 and 4.1
- Identification of 16 previously unpublished SMGs
- Derivation of median spectral line energy distribution for luminous SMGs, estimating mean gas mass of approximately (5.3 +/- 1.0) x 10^10 solar masses
- Relationship between full width at half maximum (FWHM) of the 12CO line and its luminosity in high-redshift starburst galaxies
- Assessment of star-formation efficiency within SMGs based on far-infrared luminosities
- Investigation into evolution of gas content in SMGs across different redshifts, concluding no significantly higher gas richness compared to less actively star-forming counterparts at elevated redshifts
- Exploration of interplay between gas properties, AGN activity, and supermassive black hole masses (MBH) within SMGs
- Deviation from local M_BH-sigma relation observed in SMGs

## Summary

The authors present the results of a comprehensive survey focused on 12CO emission in 40 luminous sub-millimetre galaxies (SMGs) with 850um fluxes ranging from S850 = 4 to 20 mJy. Utilizing observations conducted with the Plateau de Bure Interferometer, they successfully detect 12CO emission in 32 SMGs situated at redshifts between z~1.2 and 4.1, including the identification of 16 previously unpublished SMGs. By analyzing multiple 12CO line transitions (J_up =2 - 7), the researchers derive a median spectral line energy distribution for these luminous SMGs, enabling them to estimate a mean gas mass of approximately (5.3 +/- 1.0) x 10^10 solar masses. Notably, they uncover a fundamental relationship between the full width at half maximum (FWHM) of the 12CO line and its luminosity in high-redshift starburst galaxies, attributing this correlation to baryon-dominated dynamics within the observed regions. Furthermore, by leveraging far-infrared luminosities, the team assesses the star-formation efficiency within these SMGs and observes a steepening trend in the L'CO-LFIR relation as a function of increasing transition levels for the 12CO molecule. Through calculations involving dynamical masses and molecular gas masses, they investigate the evolution of gas content in SMGs across different redshifts, ultimately concluding that these galaxies do not exhibit significantly higher gas richness compared to less actively star-forming counterparts at elevated redshifts. Additionally, by integrating X-ray observations into their analysis, they explore the interplay between gas properties and AGN activity alongside supermassive black hole masses (MBH) within SMGs. Surprisingly, their findings reveal that SMGs deviate notably from the local M_BH-sigma relation. In summary, this research characterizes SMGs as a class of massive ultraluminous galaxies abundant in gas but displaying heterogeneous properties. These galaxies range from disc-like systems undergoing intense starburst activity with luminosities around L~10^12 solar units to some of the most vigorously star-forming mergers observed in our Universe.