Lick index system Lick index system definition at the RSS/SALTdefinition at the RSS/SALT

A.Y. Kniazev (SALT/SAAO), A.Y. Kniazev (SALT/SAAO),

O.K. Sil’chenko (SAI MSU)O.K. Sil’chenko (SAI MSU)

Lick index system is a tool to Lick index system is a tool to derive (mean) stellar derive (mean) stellar

population characteristics population characteristics through the evolutionary through the evolutionary synthesis of integrated synthesis of integrated

spectra. Can be applied to spectra. Can be applied to galaxies and stellar clusters.galaxies and stellar clusters.

The problem of equivalent width The problem of equivalent width measurements: an arbitrary continuum measurements: an arbitrary continuum

levellevel

Typical galactic Typical galactic spectra, being of F-K spectra, being of F-K spectral types, have spectral types, have NO spectral ranges NO spectral ranges free of absorption free of absorption lines, to trace safely lines, to trace safely the continuum level.the continuum level.

Lick indices: unified prescription of Lick indices: unified prescription of absorption line measurementsabsorption line measurements

The borders of lines The borders of lines and continuum bands and continuum bands for integration are for integration are fixed! (Adopted to the fixed! (Adopted to the Lick/IDS spectral Lick/IDS spectral resolution)resolution)

The description of some Lick indices: The central (`line’) band and two continuum bands

The preference of Lick indices The preference of Lick indices over the direct spectrum (SED) over the direct spectrum (SED)

fitting:fitting: No problem with (unknown internal) No problem with (unknown internal)

dust: continuum interpolation onto dust: continuum interpolation onto the absorption line centers the absorption line centers eliminates dust effect.eliminates dust effect.

The preference of Lick indices The preference of Lick indices over the direct spectrum (SED) over the direct spectrum (SED)

fitting:fitting: Even more important – independent Even more important – independent

determination of abundances of determination of abundances of VARIOUS chemical elementsVARIOUS chemical elements

Current stellar spectral libraries used in fitting Current stellar spectral libraries used in fitting contain stars with only SOLAR element contain stars with only SOLAR element abundance ratios for nearly solar metallicities abundance ratios for nearly solar metallicities (there are no other stars in the Sun vicinity), (there are no other stars in the Sun vicinity), while in external galaxies a great variety of while in external galaxies a great variety of abundance ratios is observed.abundance ratios is observed.

Massive elliptical galaxies are strongly Massive elliptical galaxies are strongly magnesium overabundant (Worthey, Faber, magnesium overabundant (Worthey, Faber,

Gonzalez 1992Gonzalez 1992))

Solid lines are SSP-models of two different ages with SOLAR Mg/Fe; the signs supplied by arrows present observed elliptical galaxies with the index radial gradients indicated

Lick system calibrationLick system calibration

To calibrate the Lick system onto the To calibrate the Lick system onto the particular spectrograph and spectral particular spectrograph and spectral resolutions, 15 standard stars from resolutions, 15 standard stars from the Worthey et al. (1994)’s list have the Worthey et al. (1994)’s list have been observed ~40 times with the been observed ~40 times with the RSS/SALT during commissioning RSS/SALT during commissioning period (2011).period (2011).

Two gratings, VPHG900 and Two gratings, VPHG900 and VPHG1800, and two slit widths, 0.6 A VPHG1800, and two slit widths, 0.6 A and 1.25 A, have been probed.and 1.25 A, have been probed.

The Lick system for the The Lick system for the VPHG900VPHG900

The index correction for the The index correction for the stellar velocity dispersion: the stellar velocity dispersion: the grating VPH900, the spectral grating VPH900, the spectral

resolution of 5.6 Aresolution of 5.6 A

The Lick system for the The Lick system for the VPHG1800VPHG1800

The index correction for the The index correction for the stellar velocity dispersion: the stellar velocity dispersion: the grating VPH1800, the spectral grating VPH1800, the spectral

resolution of 2.5 Aresolution of 2.5 A

Comparison of the Lick index profiles Comparison of the Lick index profiles measured in the lenticular galaxy measured in the lenticular galaxy NGC509 with the MPFS/BTA and NGC509 with the MPFS/BTA and

RSS/SALTRSS/SALT

Relic rings in S0 galaxies with young bulges

The kinematic profiles of NGC509 and NGC 516: the LOS velocities of the stellar component, and the stellar velocity dispersions. The SAURON LOS velocity field cut by the digital slit along the major axis is over-plotted for comparison (Krajnovic et al. 2011).

Relic rings in S0 galaxies with young bulges

The age diagnostic index-index diagrams for the disks and rings of NGC509 and NGC516. The stellar population models for [Mg/Fe]= 0.0 and five different ages, plotted by red curves and marked by log(Gyr), are plotted as the reference frame; the blue lines crossing the model metallicity sequences mark the metallicities of +0.67, +0.35, 0.00, –0.33 from right to left. Left panel: – The large-scale stellar disks, at R > 12′′ for NGC509 and at R > 7′′ for NGC516; Right panel: – the ‘relic rings’ zones, at R = 8′′ − 10′′ for NGC509 and at R = 6′′ − 7′′ for NGC516.

Further statistics: elliptical Further statistics: elliptical galaxies are calcium-galaxies are calcium-

underabundant and carbon- underabundant and carbon- and nitrogen-and nitrogen-overabundantoverabundant

Proctor & Sansom 2002

Unnoticed feature: Fe5015 contains strong Ti lines, so the Ti/Fe ratio in elliptical galaxies is also non-solar