%0 Generic %1 spiniello2013stellar %A Spiniello, Chiara %A Trager, Scott %A Koopmans, Léon V. E. %A Conroy, Charlie %D 2013 %K imf mass variation %T The stellar IMF determined in early-type galaxies from a non-degenerate set of optical line indices %U http://arxiv.org/abs/1305.2873 %X We investigate the optical spectral region of spectra of ~1000 stars searching for IMF-sensitive features to constrain the low-mass end of the initial mass function (IMF) slope in elliptical galaxies. We use the MILES stellar library in the wavelength range 3500-7500 A to select indices that are sensitive to cool dwarf stars and that only weakly depend on age and metallicity. We find several promising indices of molecular TiO and CaH lines. The use of these indicators bluer than NIR features (NaI, CaT, Wing-Ford FeH) is crucial if we want to compare our observations to optical simple stellar population models. In this wavelength range, the response of a change in the effective temperature of the cool red giant (RGB) population is similar to the response of a change in the number of dwarf stars in the galaxy. We show that it is possible to break the degeneracy between IMF variation and Teff,RGB with our new IMF indicators. We conclude that our new CaH1 index (6380A), the only indicator that comes purely from cool dwarfs, allows the determination of the low-mass end of the IMF from integrated-light measurements, when combined with different TiO lines and age- and metallicity-dependent features such as Hbeta, Mgb, Fe5270 and Fe5335. We measure line-index strengths of our new optical IMF-indicators in the Conroy & van Dokkum SSP models with ages= 3.0,13.5Gyr, a/Fe=+0.0,+0.4dex and deltaTeff,RGB=-200,+50 K. We compare these to index strengths of the same spectral features in a sample of stacked SDSS early-type galaxy spectra with varying velocity dispersions. We find a clear trend of steepening IMF with increasing velocity dispersion from 150 to 310 km/s described by the linear equation x =(2.26 +-0.08)*log(sigma200)+(2.13+-0.15),where x is the IMF slope and sigma200 is the central stellar velocity dispersion measured in units of 200 km/s.

@misc{spiniello2013stellar, abstract = {We investigate the optical spectral region of spectra of ~1000 stars searching for IMF-sensitive features to constrain the low-mass end of the initial mass function (IMF) slope in elliptical galaxies. We use the MILES stellar library in the wavelength range [3500-7500] A to select indices that are sensitive to cool dwarf stars and that only weakly depend on age and metallicity. We find several promising indices of molecular TiO and CaH lines. The use of these indicators bluer than NIR features (NaI, CaT, Wing-Ford FeH) is crucial if we want to compare our observations to optical simple stellar population models. In this wavelength range, the response of a change in the effective temperature of the cool red giant (RGB) population is similar to the response of a change in the number of dwarf stars in the galaxy. We show that it is possible to break the degeneracy between IMF variation and Teff,RGB with our new IMF indicators. We conclude that our new CaH1 index (6380A), the only indicator that comes purely from cool dwarfs, allows the determination of the low-mass end of the IMF from integrated-light measurements, when combined with different TiO lines and age- and metallicity-dependent features such as Hbeta, Mgb, Fe5270 and Fe5335. We measure line-index strengths of our new optical IMF-indicators in the Conroy & van Dokkum SSP models with ages= [3.0,13.5]Gyr, [a/Fe]=[+0.0,+0.4]dex and deltaTeff,RGB=[-200,+50] K. We compare these to index strengths of the same spectral features in a sample of stacked SDSS early-type galaxy spectra with varying velocity dispersions. We find a clear trend of steepening IMF with increasing velocity dispersion from 150 to 310 km/s described by the linear equation x =(2.26 +-0.08)*log(sigma200)+(2.13+-0.15),where x is the IMF slope and sigma200 is the central stellar velocity dispersion measured in units of 200 km/s.}, added-at = {2013-05-15T01:57:59.000+0200}, author = {Spiniello, Chiara and Trager, Scott and Koopmans, Léon V. E. and Conroy, Charlie}, biburl = {https://www.bibsonomy.org/bibtex/24a3986e18a5f5cad2e1bd67a9835e50b/miki}, description = {[1305.2873] The stellar IMF determined in early-type galaxies from a non-degenerate set of optical line indices}, interhash = {8969b8c1dbf9ebd9646f063892423351}, intrahash = {4a3986e18a5f5cad2e1bd67a9835e50b}, keywords = {imf mass variation}, note = {cite arxiv:1305.2873Comment: 15 pages, 9 figures}, timestamp = {2013-05-15T01:57:59.000+0200}, title = {The stellar IMF determined in early-type galaxies from a non-degenerate set of optical line indices}, url = {http://arxiv.org/abs/1305.2873}, year = 2013 }