3 Spectroscopy

Long-slit spectra of the individual galaxies were obtained during two different runs in September and November 2001 at the 1.82 m telescope of the Asiago Observatory (Italy) equipped with AFOSC, which has a spatial scale of 0.47 arcsec pixel^-1 over a 1k $\times$ 1k CCD. The grism n.4, chosen for its large spectral coverage, gave a dispersion of 4.2 Å pixel^-1 in the effective range of 4200-7700 Å. A slit width of 1.26 and 2.1 arcsec, selected according to the seeing conditions, produced a spectral resolution of $\sim$13 Å and 24 Å in the two runs, respectively. Typical exposure times were of 1800 s each. See Table 1 for details about the observations.

Spectra were reduced with IRAF following the usual steps of bias subtraction, flat-field correction, cosmic-rays removal, wavelength calibration by means of Helium-Argon or Thorium comparison lamps and night-sky subtraction. Finally they were flux calibrated through the observation of the spectrophotometric standard stars BD+284211 and G191-b2b. The 1D spectra obtained adding the total flux of each object with the task APALL were corrected for Galactic extinction using the value E(B-V)=0.29 derived above and applying the CCM extinction law.

Figure 4: Optical spectra of the six galaxies identified as members of the galaxy group CG J0247+44.9, labeled according to Fig. 1. Emission lines are visible in objects "a'', "c'', "d'', and "e'' with different properties (see text for a detailed description).

Radial velocities were calculated by measuring the position of the emission-lines, where detectable, or by using the cross-correlation technique Tonry & Davis (1979) when only the absorption lines were present. Six out of seven galaxies show comparable redshifts (Table 5), suggesting that they are members of a group; their spectra are shown in Fig. 4. Only in the case of galaxy "g'' (2MASXi J0247387+445008) it was impossible to apply the above methods due to the low S/N ratio of the spectrum. Nevertheless we could recognize some absorption lines by comparing the spectrum with an early-type galaxy template Kinney et al. (1996) and we estimated a redshift of $\sim$0.17. This estimate is in agreement with the observed color B-R = 2.13, considerably redder than typical colors for the same morphological type at low redshift (see e.g. Fig. 2 of Liu 1999). Therefore object "g'' appears to be a background galaxy and not a member of the group.