ISO deep far-infrared survey in the "Lockman Hole"

K. Kawara, H. Matsuhara, H. Okuda, Y. Taniguchi, Y. Sato, Y. Sofue, K. Wakamatsu, S. Oyabu, D. B. Sanders, L. L. Cowie
2004 Astronomy and Astrophysics  
We present the catalogs and source counts for the C 90 (reference wavelength of 90 µm) and C 160 (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 deg 2 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
more » ... ux 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 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 (S NR) of three or greater. The distribution of the observed associations between C 90 and C 160 sources indicates that the 1σ 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 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. light from both stars and active galactic nuclei (AGN). The far-infrared spectra of galaxies peak in the wavelength range 25-200 µm. Cirrus-dominated normal galaxies have an emission peak at 100-200 µm, while infrared-luminous starburst galaxies peak near 60 µm, and Seyfert galaxies often show a peak near 25 µm (Sanders & Mirabel 1996 and references therein). The infrared luminosity as observed by IRAS is ∼30% of the total energy output of galaxies in the local Universe (Soifer & Neugebauer 1991) . The detection of the CIB (Cosmic Infrared Background) with the COBE satellite at far-infrared and submillimeter wavelengths (e.g. Puget et al. 1996) indicates that the integrated luminosity from thermal Article published by EDP Sciences and available at
doi:10.1051/0004-6361:20031532 fatcat:5pfavaqutfamnfmfrfgi2t6zzy