  Data from the Spitzer Space Telescope (the First Look Survey - FLS) have
recently been made public. We have compared the 24 micron images with very deep
WSRT 1.4 GHz observations (Morganti et al. 2004), centred on the FLS
verification strip (FLSv). Approximately 75% of the radio sources have
corresponding 24 micron identifications. Such a close correspondence is
expected, especially at the fainter radio flux density levels, where star
forming galaxies are thought to dominate both the radio and mid-IR source
counts. Spitzer detects many sources that have no counter-part in the radio.
However, a significant fraction of radio sources detected by the WSRT (about
25%) have no mid-IR identification in the FLSv (implying a 24 micron flux
density less than 100 microJy). The fraction of radio sources without a
counterpart in the mid-IR appears to increase with increasing radio flux
density, perhaps indicating that some fraction of the AGN population may be
detected more readily at radio than Mid-IR wavelenghts. We present initial
results on the nature of the radio sources without Spitzer identification,
using data from various multi-waveband instruments, including the publicly
available R-band data from the Kitt Peak 4-m telescope.

Astrophysics