Volume 427, Number 3, December I 2004
|Page(s)||795 - 801|
|Published online||16 November 2004|
A population of extreme mid-to-near-infrared sources: Obscured AGN and dusty starbursts
Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK e-mail: firstname.lastname@example.org
2 Observatory, PO Box 14, 00014 University of Helsinki, Finland
3 European Southern Observatory, Casilla 19001, Santiago, Chile
4 Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
5 Astrophysics Group, Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2AZ, UK
Accepted: 9 August 2004
We present a sample of mid-infrared detected sources from the European Large Area ISO Survey (ELAIS) regions characterised by strong mid-IR radiation with faint near-IR and optical counterparts. These extreme mid-to-near-IR objects (EMNOs) are defined here by a flux ratio of . This population is not obvious in deeper small area ISO surveys, though it produces more than 20% of the observed cosmic IR background radiation (CIRB) at 15m above 1 mJy. Near-future large area deep mid-IR surveys with the Spitzer Space Telescope, however, are bound to uncover large amounts of these objects, which we argue to most likely be obscured AGNs, based on SED shapes and X-ray data. Very strong dusty starbursts at may also have high mid-to-near-IR flux ratios, but using the MIR/NIR and FIR/MIR ratios these may be separated. Most of our EMNOs appear to be ULIRGs, half are also extremely red objects (ERO). A curious case of a low redshift, less luminous object with a very young stellar population is also found. We predict that the simple broad band selection method makes EMNOs a useful window into high-redshift obscured nuclear activity and its sought after relation to star-formation, in a similar way that EROs have been used to define samples of high-redshift early type galaxies.
Key words: galaxies: evolution / galaxies: starburst / galaxies: active / infrared: galaxies / cosmology: observations
© ESO, 2004
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