Serbian Astronomical Journal (Dec 2009)
Measurement of the Lick Indices in Early-Type Galaxies: Line-of-Sight Velocity Distribution Corrections for IC 1459
Abstract
In this paper we analyse the measurements of the absorption line-strength Lick indices in the early-type galaxy IC 1459. We use thelong-slit spectra of the elliptical galaxy IC 1459 from which its kinematicshad previously been extracted to calculate the Lick indices forthe observed spectral region (Mg$_2$, Fe5270, Fe5335 and H$_beta$). Weapply the usual procedure and correct the indices to the Lick spectralresolution and for the zero velocity dispersion. The procedure applied in thispaper also corrects to non-Gaussian line-of-sight velocity distribution(LOSVD) observed in this galaxy, especially in its outer parts. The findingsof Kuntschner (2004) were tested and it is shown that the departures from theGaussian LOSVD may indeed cause erroneous determinations of the Lick indices. The impact of the introduction of non-Gaussian LOSVD differs for differentindices. For the galaxy IC~1459 it is shown that the iron indices areespecially sensitive when the correction due to anistropies is introduced: thecorrections for Fe5270 and Fe5335 are $sim 10$ and $sim 19$ percentlarger, respectively, than the corrections obtained in case of a pure Gaussian. The corrections for Mg$_2$ index are shown to be negligible and thecorrections of the H$_beta$ index due to anisotropies are also small (below$sim 4$ per cent at most).
