High-redshift radio galaxies from DEEP2 fields

C. H. Ishwara-Chandra1*, Susanta K. Bisoi2, Sandeep K. Sirothia1, S. Pal3,4 and P. Janardhan2
1National Centre for Radio Astrophysics, TIFR, Pune University Campus, Pune 411 007, India
2Physical Research Laboratory, Astronomy & Astrophyscis Division, Ahmedabad 380 009, India
3Indian Centre for Space Physics, Kolkata 700084, India
4Ionospheric and Earthquake Research Centre, Sitapur 721154, India

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It is now well established that the high redshift radio galaxies exhibit steep radio spectra, and hence ultra-steep spectrum radio sources provide good candidates for high-redshift radio galaxies. Nearly all of the high redshift radio galaxies have been found using this relation. We have started a programme with GMRT to exploit this correlation at flux density levels of about 10 to 100 times deeper than the known high-redshift radio galaxies. Here, we have obtained deep, high resolution radio observations at 150 MHz with GMRT for several ’deep’ fields which are well studied at higher radio frequencies and in optical, with an aim to detect candidate high redshift radio galaxies. In this work we present ultra-steep spectrum (USS) samples from two of the DEEP2 deep fields using the 150 MHz Giant Meter-wave Radio Telescope (GMRT) observations. From correlating these radio sources w.r.t to the high-frequency catalogues such as FIRST and NVSS at 1.4 GHz, and optical catalogues such as SDSS and DEEP2, we derive a list of steep spectrum (spectral index, alpha > 1) radio sources which remain undetected in SDSS and DEEP2 optical images. These are good candidates for high redshift radio galaxies and will be followed up with large optical telescopes.

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Keywords : galaxies: active - galaxies: high-redshift - radio continuum: galaxies