TY - JOUR
T1 - The stellar halos of massive elliptical galaxies. II. Detailed abundance ratios at large radius
AU - Greene, Jenny E.
AU - Murphy, Jeremy D.
AU - Graves, Genevieve J.
AU - Gunn, James E.
AU - Raskutti, Sudhir
AU - Comerford, Julia M.
AU - Gebhardt, Karl
PY - 2013/10/20
Y1 - 2013/10/20
N2 - We study the radial dependence in stellar populations of 33 nearby early-type galaxies with central stellar velocity dispersions σ* ≳ 150 km s-1. We measure stellar population properties in composite spectra, and use ratios of these composites to highlight the largest spectral changes as a function of radius. Based on stellar population modeling, the typical star at 2Re is old (∼ 10 Gyr), relatively metal-poor ([Fe/H] ≈ -0.5), and α-enhanced ([Mg/Fe] ≈ 0.3). The stars were made rapidly at z ≈ 1.5-2 in shallow potential wells. Declining radial gradients in [C/Fe], which follow [Fe/H], also arise from rapid star formation timescales due to declining carbon yields from low-metallicity massive stars. In contrast, [N/Fe] remains high at large radius. Stars at large radius have different abundance ratio patterns from stars in the center of any present-day galaxy, but are similar to average Milky Way thick disk stars. Our observations are thus consistent with a picture in which the stellar outskirts are built up through minor mergers with disky galaxies whose star formation is truncated early (z ≈ 1.5-2).
AB - We study the radial dependence in stellar populations of 33 nearby early-type galaxies with central stellar velocity dispersions σ* ≳ 150 km s-1. We measure stellar population properties in composite spectra, and use ratios of these composites to highlight the largest spectral changes as a function of radius. Based on stellar population modeling, the typical star at 2Re is old (∼ 10 Gyr), relatively metal-poor ([Fe/H] ≈ -0.5), and α-enhanced ([Mg/Fe] ≈ 0.3). The stars were made rapidly at z ≈ 1.5-2 in shallow potential wells. Declining radial gradients in [C/Fe], which follow [Fe/H], also arise from rapid star formation timescales due to declining carbon yields from low-metallicity massive stars. In contrast, [N/Fe] remains high at large radius. Stars at large radius have different abundance ratio patterns from stars in the center of any present-day galaxy, but are similar to average Milky Way thick disk stars. Our observations are thus consistent with a picture in which the stellar outskirts are built up through minor mergers with disky galaxies whose star formation is truncated early (z ≈ 1.5-2).
KW - galaxies: abundances
KW - galaxies: elliptical and lenticular, cD
KW - galaxies: evolution
UR - https://www.scopus.com/pages/publications/84886902895
UR - https://www.scopus.com/pages/publications/84886902895#tab=citedBy
U2 - 10.1088/0004-637X/776/2/64
DO - 10.1088/0004-637X/776/2/64
M3 - Article
AN - SCOPUS:84886902895
SN - 0004-637X
VL - 776
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 64
ER -