ISOCAM observations of the Hubble Deep Field reduced with the PRETI method
H. Aussel, C. J. Cesarsky, D. Elbaz, J. L. Starck;
AaA, 1999, 342, 313
ABSTRACT:We have developed a new ISOCAM data reduction technique based on wavelet analysis, especially designed for the detection of faint sources in
mid-infrared surveys.
This method, the Pattern REcognition Technique for Isocam
data (PRETI) has been used to reduce the observations of the Hubble Deep
Field (HDF) and flanking fields with ISOCAM at 6.75 (LW2) and 15 mu m (LW3)
(Rowan-Robinson et al.
\cite{RowanRobinson}).
Simulations of ISOCAM data allow us
to test the photometric accuracy and completeness of the
reduction.
According to these simulations, the PRETI source list is 95% complete in the 15 mu m
band at 200 mu Jy and in the 6.75 mu m band at 65 mu Jy, using detection
thresholds which minimize the number of false detections.
We detect 49 objects in
the ISO-HDF at high confidence secure level, 42 in the LW3 filter, 3 in the
LW2 filter, and 4 in both filters.
An additional, less secure, list of 100
sources is presented, of which 89 are detected at 15 mu m only, 7 at 6.75 mu m only
and 4 in both filters.
All ISO-HDF objects detected in the HDF itself have
optical or infrared counterparts, except for one from the additional
list.
All except one of the radio sources detected in the field by Fomalont et
al.
(\cite{Fomalont}) are detected with ISOCAM.
Using a precise correction for the field of
view distortion of ISOCAM allows us to separate blended sources.
This,
together with the fact that PRETI allows to correct data on the tail of cosmic rays
glitches, lead us to produce deeper source lists than previous authors.
Our list
of bright sources agree with those of Désert et al.
(\cite{IAS})
in both filters, and with those of Goldschmidt et
al.
(\cite{Goldschmidt}) in the LW3 filter, with systematic difference in photometry.
Number
counts derived from our results show an excess by a factor of 10 with respect to
the prediction of a no evolution model (Franceschini
\cite{Franceschini98}) in the LW3 band.
On the contrary, the number of sources in the LW2 band is
compatible with the prediction of such a model, but with greater uncertainties,
given the small number of detections.
Based on observations with the
Infrared Space Observatory (ISO).
ISO is an ESA project with instruments
funded by ESA Member States (especially the PI countries: France, Germany,
The Netherlands and the United Kingdom) and with participation of ISAS and
NASA.
KEYWORDS: infrared: galaxies, galaxies: evolution, methods: data analysis
CODE: aussel99