Issue |
A&A
Volume 413, Number 3, January III 2004
|
|
---|---|---|
Page(s) | 843 - 859 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20031532 | |
Published online | 07 January 2004 |
ISO deep far-infrared survey in the “Lockman Hole”*
III. Catalogs and source counts at 90 & 170 μm
1
Institute of Astronomy, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo, 181-0015, Japan
2
Institute of Space and Astronautical Science (ISAS), 3-1-1 Yoshinodai, Sagamihara, Kanagawa, 229-8510, Japan
3
Gunma Astronomical Observatory, Gunma 377-0702, Japan
4
Astronomical Institute, Tohoku University, Aoba, Sendai 980-77, Japan
5
Department of Physics, Gifu University, Gifu 501-11, Japan
6
Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
Corresponding author: K. Kawara, kkawara@ioa.s.u-tokyo.ac.jp
Received:
28
May
2003
Accepted:
25
September
2003
We present the catalogs and source counts for the C_90 (reference
wavelength of 90 ) and C_160 (170 ) bands, which were
extracted from our analysis of an ISO deep far-infrared survey conducted
as part of the Japan/UH ISO cosmology project. The total survey area is
~0.9 deg2 in two fields within the Lockman Hole. The analysis
consists of source extraction using the IRAF DAOPHOT package and simulations
carried out by adding artificial sources to the maps to estimate the detection
rate, the flux bias, the positional accuracy, and the noise. The flux
calibration was performed using the Sb galaxy UGC06009 –
the photometric error was estimated to be ~50% at C_90 and ~65% at C_160. The total noise
estimated from the simulation is dominated by
the confusion noise due to the high source density. The confusion noise is
~20 mJy at C_90 and ~35 mJy at C_160, which is much
larger than the instrumental noise which is at the level of a few mJy or less.
The catalogs were constructed by selecting 223 C_90 sources and 72 C_160
sources with a Signal to Noise Ratio (SNR) of three or greater. The
distribution of the observed associations between C_90 and C_160 sources
indicates that the positional errors are ~20´´ and ~35´´ at C_90 and C_160, respectively. The corrections for
the detection rate and the flux bias are significant for sources fainter than 200 mJy at C_90 and 250 mJy at C_160. Most of the sources detected both
at C_90 and C_160 have a F(C_160)/F(C_90) color redder than the Sb galaxy UGC 06009. Such a red color could result from reddening due to the flux
bias or a K-correction brightening due to the effect of redshift. Red sources
brighter than 200 mJy at C_160 may be very luminous galaxies like Arp 220
at moderate redshift. The source counts are derived by applying the
corrections for the detection rate and flux bias. The resultant counts are
quite consistent with the constraints derived from the fluctuation analysis
performed in Paper II. The C_160 counts are also consistent
with the results from the FIRBACK project. Our C_90 survey, which is 2–3 times deeper than those previously published, reveals an upturn in the
count slope at around 200 mJy. While recent models give a reasonable
fit to the C_160 counts, none of them are successful in accounting for the
upturn in the C_90 counts. If the upturn is caused by ultraluminous IR galaxies, their redshifts would need to be at
, implying a major
event in galaxy evolution at moderate redshift.
Key words: galaxies: evolution / galaxies: starburst / cosmology: observations / infrared: galaxies
© ESO, 2004
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