TY - JOUR
T1 - The puzzlingly small Ca II triplet absorption in elliptical galaxies
AU - Saglia, R. P.
AU - Maraston, Claudia
AU - Thomas, Daniel
AU - Bender, Ralf
AU - Colless, Matthew
N1 - Funding Information:
R. P. S. acknowledges the International Research Exchange fellowship that made possible his visit to the Research School of Astronomy and Astrophysics of the Australian National University in Canberra, where part of the research project described here was performed. R. P. S., R. B., C. M., and D. T. acknowledge the support by the DFG grant SFB 375. We thank S. Edwards, C. Harrison, and L. Pittroff for helping during the observations and data reduction. We acknowledge the discussion with Laura Greggio. We acknowledge the observatories that supported this project: Calar Alto (Centro Astrofisico Hispano Alemano), Siding Spring (MSSSO), and La Silla (ESO).
PY - 2002/9/30
Y1 - 2002/9/30
N2 - We measure the central values (within Re/8) of the Ca II triplet line indices CaT* and CaT and the Paschen index PaT at 8600 Å for a 93% complete sample of 75 nearby early-type galaxies with B T< 12 mag and Vgal< 2490 km s-1. We find that the values of CaT* are constant to within 5% over the range of central velocity dispersions 100 km s-1 ≤ σ ≤ 340 km s-1, while the PaT (and CaT) values are mildly anticorrelated with σ. Using simple and composite stellar population models, we show the following: (1) The measured CaT* and CaT are lower than expected from simple stellar population (SSP) models with Salpeter initial mass functions (IMFs) and with metallicities and ages derived from optical Lick (Fe, Mg, and Hβ) indices. Uncertainties in the calibration, the fitting functions, and the SSP modeling taken separately cannot explain the discrepancy. On average, the observed PaT values are within the range allowed by the models and the large uncertainties in the fitting functions. (2) The steepening of the IMF at low masses required to lower the CaT* and CaT indices to the observed values is incompatible with the measured FeH index at 9916 A° and the dynamical mass-to-light ratios of elliptical galaxies. (3) Composite stellar populations with a low-metallicity component reduce the disagreement, but rather artificial metallicity distributions are needed. Another explanation may be that calcium is indeed underabundant in elliptical galaxies.
AB - We measure the central values (within Re/8) of the Ca II triplet line indices CaT* and CaT and the Paschen index PaT at 8600 Å for a 93% complete sample of 75 nearby early-type galaxies with B T< 12 mag and Vgal< 2490 km s-1. We find that the values of CaT* are constant to within 5% over the range of central velocity dispersions 100 km s-1 ≤ σ ≤ 340 km s-1, while the PaT (and CaT) values are mildly anticorrelated with σ. Using simple and composite stellar population models, we show the following: (1) The measured CaT* and CaT are lower than expected from simple stellar population (SSP) models with Salpeter initial mass functions (IMFs) and with metallicities and ages derived from optical Lick (Fe, Mg, and Hβ) indices. Uncertainties in the calibration, the fitting functions, and the SSP modeling taken separately cannot explain the discrepancy. On average, the observed PaT values are within the range allowed by the models and the large uncertainties in the fitting functions. (2) The steepening of the IMF at low masses required to lower the CaT* and CaT indices to the observed values is incompatible with the measured FeH index at 9916 A° and the dynamical mass-to-light ratios of elliptical galaxies. (3) Composite stellar populations with a low-metallicity component reduce the disagreement, but rather artificial metallicity distributions are needed. Another explanation may be that calcium is indeed underabundant in elliptical galaxies.
KW - galaxies: elliptical and lenticular, cD
KW - galaxies: fundamental parameters
UR - http://www.scopus.com/inward/record.url?scp=0038088960&partnerID=8YFLogxK
U2 - 10.1086/344742
DO - 10.1086/344742
M3 - Article
AN - SCOPUS:0038088960
SN - 0004-637X
VL - 579
SP - L13-L16
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
ER -