http://arxiv.org/abs/1312.0046
Context. Infrared-Faint Radio Sources (IFRS) are characterised by relatively high radio flux densities and associated faint or even absent infrared and optical counterparts. The resulting extremely high radio-to-infrared flux density ratios up to several thousands were previously known only for High-redshift Radio Galaxies (HzRGs), suggesting a link between these classes of object. However, the optical and infrared faintness of IFRS makes their study diffcult. So far, no redshift is known for an original IFRS which would help to put IFRS in the context of other classes of object, especially of HzRGs.
Aims. This work tests the hypothesis that IFRS follow the relation between 3.6 um flux density and redshift found for HzRGs. Furthermore, redshifts will enable us to reveal the intrinsic radio and infrared properties of IFRS and we will test the current suggestions that IFRS are high-redshift radio-loud active galactic nuclei.
Methods. A sample of IFRS was spectroscopically observed using the Focal Reducer and low dispersion Spectrograph 2 (FORS2) at the Very Large Telescope (VLT). The data are reduced based on the Image Reduction and Analysis Facility (IRAF) and redshifts extracted from the final spectra, where possible. This required information is then used to calculate rest-frame luminosities and to perform the first spectral energy distribution modelling based on redshifts.
Results. We find three IFRS to be located at redshifts of 1.84, 2.13, and 2.76, confirming the high-redshift character of this class of object. High-ionisation emission lines with high equivalent widths and modelling of the spectral energy distribution support the hypothesis that IFRS contain radio-loud active galactic nuclei. We find IFRS being similar to HzRGs and especially observe IFRS to follow the relation between 3.6 um flux density and redshift found for HzRGs.
Tue, 3 Dec 13
46/69
You must be logged in to post a comment.