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Astron. Astrophys. 342, 665-670 (1999)

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4. Results

Our results are summarized in Table 1. Positions refer to the positions provided by the COSMOS catalog, or for sources below the COSMOS plate limit to detections on our EFOSC images, adopting the astrometry of the COSMOS plates. Position errors are about [FORMULA] r.m.s. Magnitudes [FORMULA] are values provided by COSMOS, except for [FORMULA], where magnitudes are derived from our EFOSC imaging, calibrated using the COSMOS [FORMULA] magnitudes of other sources in the field. Since this procedure ignores the differences between [FORMULA] and the Bessel B filter used in EFOSC, [FORMULA] for this object is only approximate. Far-IR luminosities [FORMULA] have been calculated from [FORMULA] where [FORMULA] is the luminosity distance and


(see Sanders & Mirabel 1996 and references therein). This procedure somewhat underestimes the total far-IR luminosity because it does not include a K-correction. An accurate K-correction is not possible because of the lack of knowledge of the SED of the sources. However, under the assumption that the SED is similar to that of the prototypical ULIG [FORMULA], we find that the underestimate introduced by Eq. (4) could be up to 50% for the most distant objects.


Table 1. Parameters of distant FSC sample sources

Notes on individual sample sources:

  • [FORMULA]: while classified as only one galaxy by COSMOS, this system consists of 2 interacting galaxies at [FORMULA]. The compound spectrum shows strong [[FORMULA]] 3727Å, in addition to [[FORMULA]] 3869Å, [[FORMULA]] 5007Å and [FORMULA].

  • [FORMULA]: the object with the highest likelihood ratio in this field, and therefore the a priori most likely counterpart, was found to be a luminous object showing [[FORMULA]], [[FORMULA]], Ca H and K absorption, and a 4000Å break at [FORMULA].

  • [FORMULA]: the second most likely counterpart as indicated by our identification process, barely resolved at [FORMULA], and showing strong [[FORMULA]], in addition to H[FORMULA] and [[FORMULA]].

  • [FORMULA]: none of the possible COSMOS identifications showed emission lines, but a fainter object close to the IRAS error ellipse was found to have [[FORMULA]] 3426Å and [[FORMULA]] at [FORMULA]. A broad feature at the expected wavelength of [FORMULA] 2798Å may also be present.

  • [FORMULA]: spectra of two galaxies only [FORMULA] apart yielded redshifts of 0.380 and 0.529, based on strong [[FORMULA]], H[FORMULA] and [[FORMULA]] lines (for both objects) and also strong [FORMULA], [[FORMULA]] 6584Å and [[FORMULA]] 6716 and 6731Å lines (in the object at [FORMULA]). The two objects are of closely similar [FORMULA] magnitude. Either of these may be the correct identication, or they may both contribute part of the FSC 60 µm flux density. In either case at least one of the objects is a ULIG, but none is a HyLIG.

  • [FORMULA]: the most likely identication from the COSMOS plate is a distorted object outside but close to the FSC error ellipse showing [[FORMULA]] and [[FORMULA]] at [FORMULA].

In addition, we observed one object not in our sample of 6 candidate distant objects, [FORMULA], in order to check possible misidentification, since the only likely counterpart was classified by COSMOS as a fairly bright star with low axial ratio. However, this object is in fact a [FORMULA] galaxy with a possible tail or extension towards the east, and showing [[FORMULA]], [[FORMULA]], H[FORMULA] and [[FORMULA]] emission lines at [FORMULA]. The COSMOS position for this object is R.A. (1950) = [FORMULA], Dec. (B1950) = [FORMULA] and its far-IR luminosity is [FORMULA]. Accounting for the flux beyond 100 µm, this object is also a ULIG.

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© European Southern Observatory (ESO) 1999

Online publication: February 23, 1999