Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004a%26a...413..843k&link_type=abstract
Astronomy and Astrophysics, v.413, p.843-859 (2004)
Astronomy and Astrophysics
Astrophysics
19
Galaxies: Evolution, Galaxies: Starburst, Cosmology: Observations, Infrared: Galaxies
Scientific paper
We present the catalogs and source counts for the C90 (reference wavelength of 90 μm) and C160 (170 μm) 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 UGC 06009 - the photometric error was estimated to be ˜50% at C90 and ˜65% at C160. 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 C90 and ˜35 mJy at C160, 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 C90 sources and 72 C160 sources with a Signal to Noise Ratio (SNR) of three or greater. The distribution of the observed associations between C90 and C160 sources indicates that the 1 σ positional errors are ˜20 arcsec and ˜35 arcsec at C90 and C160, respectively. The corrections for the detection rate and the flux bias are significant for sources fainter than 200 mJy at C90 and 250 mJy at C160. Most of the sources detected both at C90 and C160 have a F(C160)/F(C90) 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 C160 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 C160 counts are also consistent with the results from the FIRBACK project. Our C90 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 C160 counts, none of them are successful in accounting for the upturn in the C90 counts. If the upturn is caused by ultraluminous IR galaxies, their redshifts would need to be at z ˜ 0.5, implying a major event in galaxy evolution at moderate redshift.
Based on observations with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries: France, Germany, The Netherlands, and the UK) and with the participation of ISAS and NASA.
Cowie Lennox L.
Kawara Kimiaka
Matsuhara Hideo
Okuda Haruyuki
Oyabu Shinki
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