Search for OH megamasers at redshift z ~ 1.7 in the GOODS-North field

Abstract

OH Megamasers (OHMs), including four spectral lines at 1.6 GHz, arise in the central dust torus of a galaxy. OHMs trace several astrophysical processes; they: (i) signal a speci c stage in the merger process of gas rich galaxies. (ii) are useful in determining extragalactic magnetic elds, and (iii) signpost galaxies with extreme star formation. They are rare phenomena in the local universe, but are expected to be more luminous and more numerous in the distant universe at z = 1-2. However, sensitivity and radio frequency interference (RFI) at low frequencies are the major limiting factors for surveys of distant OHMs. International e orts have come together to generate multi-wavelength data on particular regions in the sky free from contamination by strong Galactic sources. It is now possible to carry out comprehensive studies of the distant, and hence early, Universe by comparing the properties of sources across the entire electromagnetic spectrum. Great Origins Observatory Survey (GOODS) is such an e ort which has generated data in two celestial regions (one each in the Northern and Southern hemisphere) at wavelengths ranging from radio to X-ray. The GOODS-North eld was observed for 5 nights at 610 MHz during May and June, 2009, using the Giant Meterwave Radio Telescope (GMRT). Our aim in this project is to detect OHM emission at redshift z ∼ 1.7 in the GOODS-North eld. The analysis of the data was done using the software package AIPS (Astronomical Image Processing System) developed by NRAO, and in-house tools developed for RFI excision and high sensitivity imaging. We have reached close to the required image noise of 10μJy, which is among the best currently achieved anywhere. We are addressing some image analysis issues to improve the image sensitivity further. The detection of megamasers at high redshifts will open the doors to a variety of studies of the early Universe. Since, the maser phenomenon is predicted to be stronger and more numerous at high redshift, even the lack of detection will be an important input into the models of galaxy evolution.