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5 Redshifts and line parameters

  Due to the large wavelength coverage of the spectra, more than one emission line is detected in most of the cases of objects classified as QSOs, Seyfert 1 galaxies or NELGs, providing secure identifications. When possible three prominent emission lines were selected, preferentially unresolved features far from the border of the spectra where the wavelength calibration is possibly less reliable. A Gaussian profile was fitted to those lines (see Table 1, Col. 8) so as to determine their centroid, and the AGN's redshift was computed by averaging the redshift of the individual lines. In Table 1 (Col. 9), redshift values are vacuum and given in the heliocentric rest frame. The formal error on them is typically of the order of 0.1 nm or $\Delta z\sim 10^{-3}$, except for OMHR 120857 and HS 1307+2623 where one (or two) broad and somewhat asymmetric line(s) lead(s) to a larger centering error (up to $\Delta z=0.01$).

Table 2 displays the measurements of the line parameters for the entire sample of emission-line objects. The numbers of Col. 1 are the same as in Col. 1 of Table 1. The equivalent width $W_{\lambda_{\rm r}}$ of the detected lines (Col. 3) and their full width at half-maximum FWHM (Col. 4) are both corrected from redshift (rest frame values); FWHM is in addition corrected for the instrumental response. No FWHM value is given for unresolved lines.

  
Table 2: Emission-line measurements

\begin{table}
$^{\ast}$\space Gaussian fit inappropriate/impossible for this line.\end{table}

The classification of the NELGs can be made on the basis of diagnostic diagrams which discriminate between different physical processes [(Baldwin et al. 1981)]: either photoionization by a non-thermal power-law continuum in a narrow-line AGN (i.e. Seyfert 2 galaxies and LINERS), or photoionization due to UV photons emitted by hot OB stars (i.e. HII region galaxies). We have computed flux ratios for the most important diagnostic lines [(Veilleux & Osterbrock 1987)]. Criteria involving ratios between adjacent lines were used to get rid as much as possible of extinction problems. From the [OIII]/H$\beta$ - [SII]/H$\alpha$ diagram, all 4 NELGs turn out to be unambiguously objects with a HII-like spectrum. The diagnostics based on [OIII]/H$\beta$ - [NII]/H$\alpha$ and [OIII]/H$\beta$ - [OI]/H$\alpha$ diagrams are a bit less certain given the errors in the measured fluxes, but give results which are consistent with this classification.


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