Characterizing Dusty Starbursts at z=2.2 in a High Density Field

Our APEX-LABOCA 870micron imaging of the proto-cluster field of the radio galaxy MRC1138-262 - the so-called Spiderweb Galaxy - at z=2.16 has uncovered 16 submillimeter galalxies (SMGs) with fluxes of S_870micron>=3mJy. The number counts indicate an excess of SMGs compared to blank fields. Based on an exquisite multi-wavelength dataset including radio and infrared observations, we conclude that in total at least seven of these 16 sources are part of this proto-cluster at z=2.2. Near-infrared spectroscopic observations (Halpha line) confirmed redshifts of z=2.16 for four of these SMGs. We request CO(1-0) observations of these four LABOCA sources identified to be part of the proto-cluster structure. We aim to characterize the general properties of the cold molecular gas reservoir: mass, gas depletion time scale, star formation efficiency and dynamics. We will compare the properties of our SMGs located in a high density region with dusty starbursts selected from blank fields, probing environmental-dependent evolution. Studying the molecular gas properties of the individual proto-cluster members will enable us to characterize in more detail the overall properties of this proto-cluster. The proposed observations will pave the road both for future ALMA follow-up observations of higher CO transitions and subsequent JVLA observations at higher spatial resolution.