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We present the largest spectroscopic follow-up performed in SWIRE ELAIS-N1. We were able to determine redshifts for 289 extragalactic sources. The values of spectroscopic redshifts of the latter have been compared with the estimated values from our photometric redshift code with very good agreement between the two for both galaxies and quasars. Six of the quasars are hyperluminous infrared (IR) galaxies all of which are broad-line active galactic nuclei. We have performed emission-line diagnostics for 30 sources using the [O iii]/Hβ, [N ii]/Hα and [S ii]/Hα line ratios in order to classify these 30 sources into star forming, Seyferts, composite and LINER and compare the results to the predictions from our spectral energy distribution template fitting methods and mid-IR selection methods. [ABSTRACT FROM AUTHOR]

Focuses on the use of spectroscopy and broad-band photometric redshifts on the distribution of Hercules sample of millijansky radio sources. Evolution of luminosity functions; Measurement of the steep-spectrum quasars; Observation of the stellar structure.

The results are presented of an extensive programme of optical and infrared imaging of radio sources in a complete subsample of the Leiden–Berkeley Deep Survey. The LBDS Hercules sample consists of 72 sources observed at 1.4 GHz, with flux densities S[sub 1.4]⩾1.0 mJy, in a 1.2 deg[sup 2] region of Hercules. This sample is almost completely identified in the g, r, i and K bands, with some additional data available at J and H. The magnitude distributions peak at r≃22 mag, K≃16 mag and extend down to r≃26 mag, K≃21 mag. The K-band magnitude distributions for the radio galaxies and quasars are compared with those of other radio surveys. At S[sub 1.4 GHz]≲1 Jy, the K-band distribution does not change significantly with radio flux density. The sources span a broad range of colours, with several being extremely red (r-K≳6). Though small, this is the most optically complete sample of mJy radio sources available at 1.4 GHz, and is ideally suited for studying the evolution of the radio luminosity function out to high redshifts. [ABSTRACT FROM AUTHOR]