ATNF Marsfield Lecture Theatre

Omar Lopez-Cruz

Submillimeter Galaxies Behind the Bullet Cluster - Omar Lopez-Cruz joint AAO/ATNF Colloquium

Clusters of galaxies allow us to detect and resolve lensed background galaxies that would otherwise be too faint for direct observation. While such galaxies are responsible for most of the sub-mm and far-infrared backgrounds (e.g. Blain 1997) that are now being resolved by Herschel Space Observatory (e.g. Eales et al. 2010), the properties of individual sources at redshifts z>1 are still poorly known. Radio observations of galaxies observed at high redshift are mostly biased toward active galactic nuclei and ultraluminous systems. We will present the results of deep observations of the submm continuum emission at 870mm of the Bullet Cluster field using the Large APEX BOlometer CAmera on the Atacama Pathfinder EXperiment (APEX) telescope. In total, seventeen point-like sources were found. Thirteen of them lie in the central 10 arcmin of the map, which has a pixel sensitivity of 1.2 mJy per beam. After correction for flux boosting and gravitational lensing, the number counts are consistent with published submm measurements. Nine of the sources have infrared counterparts in Spitzer maps. The strongest submm detection (S1) coincides with a source previously reported at other wavelengths. S1 has a reported spectral redshift z = 2.791 ± 0.007 (Gonzalez et al. 2010) determined using PAH transitions. We present the first CO (J = 1á–0, J = 3á–2) detections using the Australian Telescope Compact Array and the Compact Array Broadband Backend receiver. We have been able to refine the redshift to z=2.7795 ± 0.0010. S1 submm flux arises from two images of a galaxy magnified by a total factor of about 100, we present first time confirmation that those two components are at the same redshift. Hence, its intrinsic flux is around 0.6 mJy at 870mm. This means that S1 is not an ultraluminous system. We comment that S1 is a rather common gas-rich, star-forming galaxy and suggest that these type of galaxies might be more representative of the overall galaxy population at z~3.