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Astron. Astrophys. 343, 389-398 (1999)

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5. Summary of ISO identifications

A total of 54 mid-IR sources were detected in a deep survey of the CFRS 1415+52 field with ISOCAM. The reliability of the detections of these predominantly very faint sources has been strengthened through comparison of the results of two completely independent analyses of the data. The counts at 6.75µm are in a very good agreement with those of the Deep ISOCAM Survey (Lockman-Hole Survey) which is [FORMULA] 0.22 counts per sq. arcmin for [FORMULA]Jy. Further support for the reliability of the identifications is provided by the properties of their optical counterparts:

  • In the CFRS 1415+52 field, there are only 25 radio-sources with [FORMULA] (Hammer et al. 1995) and 34 ISOCAM sources with [FORMULA] which are identified with [FORMULA] galaxies (out of a total of [FORMULA]600 [FORMULA] objects). Based only on optical-IR astrometry six ISOCAM sources are associated with radiosources, and the cumulative probability of finding 6 or more radiosources in this sample by chance is only 0.0037.

  • Among the 15 galaxies with spectra, 6 (40%) are found to be AGNs, even though only 7% of CFRS galaxies are AGN (Hammer et al. 1997).

  • Of the star-forming galaxies, 7 out of 8 have a Balmer index larger than the median value of CFRS galaxies, possibly implying a relationship between the presence of dust and the A-star population. Also dusty galaxies present larger color indices (Flores et al., 1998)

  • The ISO galaxies have a median [FORMULA] color which is 0.5 mag redder than randomly-selected CFRS galaxies and 5 of them have a very red [FORMULA] color.

Clearly, the ISOCAM LW2 sources have different average properties than a random sample of CFRS galaxies, giving additional confidence in our detections, even down to [FORMULA].

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© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999