Orateur
Description
It is broadly accepted that CO is a reliable tracer of molecular H in massive IR ($L_{\rm IR}\ \ge\ 10^9\ L_{\odot}$) galaxies, and that there are clear correlations between $L_{\rm IR}$ and $L'_{\rm CO}$ that are qualitatively independent of environment and even redshift. We present two tales on the search for $^{12}$CO emission from dusty star-forming galaxies in both field (Lockman Hole, z $<$ 0.1) and cluster (Zw Cl0024.1+1652, z $\sim$ 0.4) environments, according to the capabilities of the EMIR receiver at the IRAM-30m telescope. The observed galaxies are part of two follow-up programs in the millimetre regime of the spectroscopic Lockman-SpReSO and GLACE surveys in the optical (OSIRIS / 10.4m GTC). From these data we derived $L_{\rm IR}$ and $L'_{\rm CO}$ estimations and put them in the framework of the historic records according to the literature for each environmental case. Among others, the results suggest that the reservoir of cold gas is smaller in cluster galaxies than in the field at a given star formation rate (SFR). Furthermore, there is also evidence that the amount of cold gas increases with the cluster-centric distance, hence pointing to an environmental dependency. Finally, we provide insights about some practical limits of the current facilities (IRAM observatories, ALMA, LMT) to get reliable $L'_{\rm CO}$ estimations for IR at low and intermediate redshifts.
