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Дата изменения: Tue Feb 8 09:57:26 2000
Дата индексирования: Sat Sep 11 20:33:20 2010
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Поисковые слова: arp 220

Line parameter measurements

In the final spectra, redshifts and line fluxes are measured within MIDAS, applying Gaussian fitting to the emission lines. To determine redshifts for individual galaxies, averages are taken over the prominent individual emission lines (mostly H$\beta$, H$\alpha$, [O III]$\lambda$4959,5007 Å). The line [O II]$\lambda$3727 Å is not included in the redshift determination since for most of the objects its observed wavelength is determined with significantly larger uncertainties due to the extrapolation of the linear scale below the first line of the reference spectrum (He I$\lambda$3889 Å ). However [O II]$\lambda$3727 Å was used to determine the redshift in rare cases where it is the only strong emission line. The errors of the redshift in such cases can be several times larger than the typical one (compare Table 2).

To improve the accuracy of the redshift determination for the Calar Alto spectra, and further, to reduce possible small systematic shifts in the zero point of the wavelength calibration, we additionally checked the wavelengths of night sky emission lines on the 2-D spectra at the position of the object spectrum. If some measurable shift was detected it was incorporated in measurements of emission line positions.

The emission line fluxes are computed by summing up the pixel intensities inside the line region applying standard MIDAS program tools. For all spectra, the individual emission line fluxes of the H$\alpha$, [N II] $\lambda\lambda$6548,6583 Å and [S II] $\lambda\lambda$6716,6731 Å line blends are obtained by summing up pixel intensities over the total blend and then modeling the individual line fluxes using Gaussian fitting.