Radial trends in imf-sensitive absorption features in two early-type galaxies: Evidence for abundance-driven gradients
- Institute for Astronomy, University of Hawaii at Mānoa, Honolulu, HI (United States)
Samples of early-type galaxies show a correlation between stellar velocity dispersion and the stellar initial mass function (IMF) as inferred from gravity-sensitive absorption lines in the galaxies’ central regions. To search for spatial variations in the IMF, we have observed two early-type galaxies with Keck/LRIS and measured radial gradients in the strengths of absorption features from 4000–5500 Å and 8000–10000 Å. We present spatially resolved measurements of the dwarf-sensitive spectral indices Na I (8190 Å) and Wing-Ford FeH (9915 Å), as well as indices for species of H, C{sub 2}, CN, Mg, Ca, TiO, and Fe. Our measurements show a metallicity gradient in both objects, and Mg/Fe consistent with a shallow gradient in α-enhancement, matching widely observed trends for massive early-type galaxies. The Na I index and the CN{sub 1} index at 4160 Å exhibit significantly steeper gradients, with a break at r∼0.1 r{sub eff} (r∼300 pc). Inside this radius, Na I strength increases sharply toward the galaxy center, consistent with a rapid central rise in [Na/Fe]. In contrast, the ratio of the FeH to Fe index strength decreases toward the galaxy center. This behavior cannot be reproduced by a steepening IMF inside of 0.1 r{sub eff} if the IMF is a single power law. While gradients in the mass function above ∼0.4 M{sub ⊙} may occur, exceptional care is required to disentangle these IMF variations from the extreme variations in individual element abundances near the galaxies’ centers.
- OSTI ID:
- 22890078
- Journal Information:
- Astrophysical Journal, Vol. 821, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
Similar Records
EVIDENCE FOR A MILD STEEPENING AND BOTTOM-HEAVY INITIAL MASS FUNCTION IN MASSIVE GALAXIES FROM SODIUM AND TITANIUM-OXIDE INDICATORS
THE STELLAR INITIAL MASS FUNCTION IN EARLY-TYPE GALAXIES FROM ABSORPTION LINE SPECTROSCOPY. II. RESULTS