Searching for a gigamaser in APM08279+5255, and other short stories

Abstract

Bolometer arrays on large antennas at high, dry sites have unveiled a dusty population of massive, luminous galaxies - submillimetre galaxies, or SMGs - which make a significant contribution to the star-formation rate density at z > 1. The most crucial piece of information required to derive the history of obscured star formation is the redshift distribution of this galaxy population, N(z), which breaks degeneracies in the models and allows the mass and dynamics of the galaxies to be explored via high-resolution three-dimensional imaging in CO and by determining their level of clustering. Many SMGs are extremely faint, optically; some have no plausible counterparts, even in the IR, making the determination of an unbiased N(z) very difficult. The arrival of Herschel and next-generation ground-based submm cameras will likely exacerbate this so-called `redshift deadlock'. Here, we report the first test of a new method for determining redshifts, based on the observed dependence of maser and IR luminosities. We have searched the dusty, lensed, hyperluminous quasar, APM08279+5255, for the 1612-, 1665- and 1667-MHz hydroxyl lines as well as the 22-GHz water line. At z = 3.9 these are shifted to 329, 340 and 4,538MHz. Our relatively shallow test data reveal no convincing maser activity but we set a meaningful constraint on the OH maser luminosity and we approach the expected thermal noise levels, meaning progress is possible. As an aside, we present deep new submm and radio imaging of this field. Using a simple shift-and-add technique we uncover a new submm galaxy, conceivably at the redshift of APM08279+5255.