Issue |
A&A
Volume 419, Number 3, June I 2004
|
|
---|---|---|
Page(s) | L49 - L53 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20040143 | |
Published online | 07 May 2004 |
Letter to the Editor
Mid-infrared selection of AGN *
1
Astronomisches Institut, Ruhr-Universität Bochum (AIRUB), Universitätsstr. 150/NA7, 44780 Bochum, Germany
2
European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
3
HERSCHEL Science Centre, ESA, Noordwijk, PO Box 299, 2200 AG Noordwijk, The Netherlands
4
Department of Mathematics, Appl. Math. & Astronomy, University of South Africa, PO Box 392, Pretoria 0003, South Africa
5
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
6
XMM-Newton Science Operation Center, ESA, Vilspa, Apartado 50727, 28080 Madrid, Spain
Corresponding author: M. Haas, haas@astro.rub.de
Received:
26
February
2004
Accepted:
15
April
2004
Since a large fraction of active galactic nuclei (AGN) is
missed in common UV-excess surveys and is even hard to find in radio,
near-IR and X-ray surveys, we have used a new AGN selection
technique which is expected to be
not affected by extinction. Within the scientific
verification of the ISOCAM Parallel Survey at m we
have discovered objects with exceptional mid-infrared (MIR)
emission. They are essentially not detected on IRAS-ADDSCANs and only
very few of them show up in the NVSS and FIRST radio
surveys. Various colour criteria of the
m data with 2MASS
and optical wavebands show that the sources
reach more extreme IR colours than the sources in the Hubble
Deep Field-South and the ELAIS survey. The comparison with
known object types suggests that we have found AGN with a pronounced
MIR emission, probably due to circum-nuclear dust. First
results from optical spectroscopy of ten candidates corroborate this
interpretation showing four AGN, two reddened LINER and four extremely
reddened emission-line galaxies with MIR/FIR flux ratios higher than
for known pure starburst galaxies. The results will make a significant
contribution to the debate on the entire AGN population.
Key words: galaxies: fundamental parameters / galaxies: photometry / quasars: general / infrared: galaxies
Based on observations with the Infrared Space Observatory ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and UK) and with the participation of ISAS and NASA, and also based on observations at the South African Astronomical Observatory SAAO.
© ESO, 2004
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