K. Kawara 1, Y. Sato 2,3, H. Matsuhara 2, Y. Taniguchi 4, H. Okuda 2, Y. Sofue 1, T. Matsumoto 2, K. Wakamatsu 5, L.L. Cowie 6, R.D. Joseph 6, & D.B. Sanders 6
1 Institute of Astronomy, The University of Tokyo
2 Institute of Space and Astronautical Science (ISAS)
3 ISO Science Operations Centre, Astrophysics Division of ESA
4 Astronomical Institute, Tohoku University
5 Department of Physics, Gifu University
6 Institute for Astronomy, University of Hawaii
As part of the Japan/UH cosmology program, we have carried out a 95 and 175
micron survey in the Lockman Hole to search for heavily obscured IR galaxies
and quasars at high redshifts. Two
fields were selected, resulting
in a total survey area of about a 1.1 square degree. As writing this abstract,
the flux calibration is quite uncertain; the flux scaling based on a bright
IRAS source in the surveyed area gives brighter fluxes than those derived from
the COBE background measurements by a factor of 3.5 for 95 micron fluxes and
2.5 for 195 micron fluxes. When based on the bright IRAS source, 3 sigma
flux levels are estimated to be about 30 mJy at 95 micron and 40 mJy at
175 micron. It is likely that far-infrared sources found in the present survey
are galaxies from the following reasons; (1) the Gautier et al's model for IR
cirrcus confusion predicts one sigma confusion to be 0.14 and 1.7 mJy at 95
and 175 micron respectively, implying a probability of having a IR cirrus peak
brighter than the detection limits is very low; (2) the angular correlation
analysis done by Matsuhara et al. (presented in this conference) shows that the
index of the spacial power spectrum significantly differ from those for the
IR cirrus. The cumulative counts of sources down to 150 mJy are
1.1 105 sources sr-1 at 95 micron and 1.5 105 sources sr-1
at 175 mircron. The number density
of 175 micron sources is 3 - 10 times higher than expected from no-evolution of
galaxies. We will also present the log(N) vs log(S) diagrams to compare with
our data with various models of galaxy counts in the far-infrared, and discuss
the implications for galaxy evolution.