Observations of the Hubble Deep Field with the Infrared Space Observatory. III. Source counts and P(D) analysis

摘要

We present source counts at 6.7 micron and 15 micron from our maps of theHubble Deep Field region, reaching 38.6 microJy at 6.7 micron and 255 microJyat 15 micron. These are the first ever extra-galactic number counts to bepresented at 6.7 micron and are 3 decades fainter than IRAS at 12 micron. Bothsource counts and a P(D) analysis suggest we have reached the ISO confusionlimit at 15 micron: this will have important implications for future spacemissions. These data provide an excellent reference point for other ongoing ISOsurveys. A no-evolution model at 15 micron is ruled out at >3 sigma, while twomodels which fit the steep IRAS 60 micron counts are acceptable. This providesimportant confirmation of the strong evolution seen in IRAS surveys. One ofthese models can then be ruled out from the 6.7 micron data.