Issue |
A&A
Volume 427, Number 3, December I 2004
|
|
---|---|---|
Page(s) | 795 - 801 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20041616 | |
Published online | 16 November 2004 |
A population of extreme mid-to-near-infrared sources: Obscured AGN and dusty starbursts
1
Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK e-mail: phjohans@ast.cam.ac.uk
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
Received:
10
May
2004
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 15
m 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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