Astronomical Science Coccato L. et al., Counter-rotating Stellar Discs in Galaxies '` ,F ( Figure 1. Fit of the galaxy spectrum (black) in a spatial bin. The best-fitting model (green) is the sum of the spectra of the ionised gas component (magenta) and the two stellar components (blue and red). The differences in the position of absorption line features and in the HÎ˛ equivalent widths between the two stellar components (indicating different kinematics and stellar population content) are clearly evident. %D ( -NQL@KHRDC kTW 6@UDKDMFSG Ă„ are younger, more metal-poor, and have higher abundances of Îą-elements than the main stellar discs. 2007). The combination of the collecting power of an 8-metre-class telescope, the large wavelength coverage (4150â€“6200 Ă…) and the high spectral resolution (full width half maximum [FWHM] of 2.0 Ă…) with the HR-blue grism makes VIMOS on the VLT the best-suited integral field unit for this kind of study. -&" [Îą/Fe] 3.6 Âą 0.6 2.0 Âą 0.5 âˆ’0.04 Âą 0.03 âˆ’0.15 Âą 0.07 0.09 Âą 0.02 0.18 Âą 0.03 NGC 4550 Main: Secondary: 6.9 Âą 0.6 6.5 Âą 0.5 âˆ’0.01 Âą 0.03 âˆ’0.13 Âą 0.04 0.20 Âą 0.02 0.28 Âą 0.02 NGC 5719 Main: Secondary: 4.0 Âą 0.9 1.3 Âą 0.2 0.08 Âą 0.02 0.3 Âą 0.02 0.10 Âą 0.02 0.14 Âą 0.02 FD &XQ FD &XQ : _ < %D FD &XQ FD &XQ :9 l l JOB l 61 @QBRDB l l ' FD &XQ < FD &XQ :9 l ' :9 :9 < '< ' : FD &XQ l < 9 ' < ,@HM BNLONMDMS l :_ % D< ,F%D Ă„ :9 :9 :9 ' < l -&" 8 @QBRDB l :9 ' < l ' < ' < D< ' < ,FA Ă„ l l OB l l 34 l l l l l 7 @QBRDB 5 JL R The Messenger 151 â€“ March 2013 l l l l 7 @QBRDB 5 JL R l l l l 7 @QBRDB 5 JL R (NMHRDC F@R -&" 8 @QBRDB - : :9 % _ 2DBNMC@QX BNLONMDMS -&" 8 @QBRDB [Z/H] FD &XQ '` Ă„ 6#$" @QBRDB :_ %D< Age [Gyr] NGC 3593 Main: Secondary: the kinematics and the Lick indices of the fitted components. The measured kineÂmatics are used to construct the twodimensional velocity fields, where the structure of the adopted spatial binning is still visible, and the counter-rotation between the two stellar components is remarkable (lower panels). The Lick indices are shown in the diagnostic plots (upper right panels) with the predictions of single stellar population models (Thomas et al., 2011). We use HÎ˛ and the combined [MgFe]: = âˆš(Mgb Âˇ [0.82 Âˇ Fe5270 + 0.28 Âˇ Fe5335]) index as indicator of stellar age and metallicity. We also take into account the variation in the abundance of Îą-elements and metallicity by measuring Table 1 summarises the mean properties of the two counter-rotating stellar populations, and Figures 2, 3 and 4 illustrate our results. In these figures, the extension of the VIMOS/IFU field of view is plotted over the galaxy image (upper-left panels). The collected spectra are then spatially binned over the field of view with the Voronoi Âbinning technique to increase the signalto-noise ratio (see Coccato et al. [2013] for further details). The spectral decomposition technique is then applied on the spectrum of each spatial bin to measure In all the sample galaxies, we confirm the presence of two stellar discs of comparable size, and one ionised gas component. The secondary stellar component and the ionised gas component counter-rotate with respect to the main stellar disc. Moreover, in all the observed galaxies, these counter-rotating secondary components Table 1. Luminosity-weighted values for the stellar population parameters of the stellar discs. %D Ă„ Figure 2. Results of the spectroscopic decomposition of NGCÂ 3593. The top left panel shows the galaxy image with the location of the VIMOS observed field of view. The bottom panels show the two-dimensional kinematics of the main, secondary and ionised gas components, respectively. The top-right panels show the measured equivalent width of the Lick indices; grids with the predictions from single stellar population models are also shown. The crosses on the top-right side of the panels show the mean error bars on the measured indices. Each spatial bin returns two sets of Lick indices, one for each stellar component: red symbols represent the main stellar component, whereas blue symbols represent the secondary counter-rotating component.