Carbon and Nitrogen Abundances in Early-type Galaxies

Abstract

For the first time, we undertake a systematic examination of the nitrogen abundances for a sample of 35 early-type galaxies spanning a range of masses and local environment. The nitrogen-sensitive molecular feature at 3360Åhas been employed in conjunction with a suite of atomic- and molecular-sensitive indices to provide unique and definitive constraints on the chemical content of these systems. By employing NH3360, we are now able to break the carbon, nitrogen, and oxygen degeneracies inherent to the use of the CN-index. We demonstrate that the NH3360 feature shows little dependency upon the velocity dispersion (our proxy for mass) of the galaxies, contrary to what is seen for carbon- and magnesium-sensitive indices. At face value, these results are at odds with conclusions drawn previously using indices sensitive to both carbon and nitrogen, such as cyanogen (CN). With the aid of stellar population models, we find that the N/Fe ratios in these galaxies are consistent with being mildly-enhanced with respect to the solar ratio. We also explore the dependence of these findings upon environment, by analyzing the co-added spectra of galaxies in the field and the Coma cluster. We confirm the previously found differences in carbon abundances between galaxies in low- and high-density environments, while showing that these differences do not seem to exist for nitrogen. We discuss the implications of these findings for the derivation of the star formation histories in early-type galaxies, and for the origin of carbon and nitrogen, themselves.

5 pages, 2 figures. Accepted by ApJ Letters

References in corpus (15)

• Stellar population synthesis at the resolution of 2003
• SparsePak: A Formatted Fiber Field Unit for The WIYN Telescope Bench Spectrograph. I. Design, Construction, and Calibration
• Stellar evolution with rotation VIII: Models at Z = 10^{-5} and CNO yields for early galactic evolution
• Population Synthesis in the Blue IV: Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations
• Oxygen, Carbon and Nitrogen evolution in galaxies
• A strong case for fast stellar rotation at very low metallicities
• Measuring Ages and Elemental Abundances from Unresolved Stellar Populations: Fe, Mg, C, N, and Ca
• Stellar populations of early-type galaxies in different environments I. Line-strength indices
• The star formation history of early-type galaxies as a function of mass and environment
• Carbon Nitrogen, and Oxygen Galactic Gradients: A Solution to the Carbon Enrichment Problem
• Formation & evolution of the Galactic bulge: constraints from stellar abundances
• Line Strengths in Early-Type Cluster Galaxies at z=0.33: Implications for alpha/Fe, Nitrogen and the Histories of E/S0s
• Differences in carbon and nitrogen abundances between field and cluster early-type galaxies
• The Chemical Evolution of Magnesium Isotopic Abundances in the Solar Neighbourhood
• Secondary Episode of Star Formation in Elliptical Galaxies

Cited by in corpus (9)

• UV-extended E-MILES stellar population models: young components in massive early-type galaxies
• The Assembly Histories of Quiescent Galaxies Since z=0.7 from Absorption Line Spectroscopy
• Exploring the Star Formation History of Elliptical Galaxies: Beyond Simple Stellar Populations with a New Estimator of Line Strengths
• Individual Alpha Elements, C, N, and Ba in Early Type Galaxies
• Abundance ratios in red-sequence galaxies over a wide mass range: The "X-planes" for magnesium, calcium, carbon and nitrogen
• Revealing O VII from stacked X-ray grating spectra of clusters, groups and elliptical galaxies
• Evidence for intermediate-age stellar populations in early-type galaxies from K-band spectroscopy
• Stellar mass-loss, rotation and the chemical enrichment of early type galaxies
• NH and Mg Index Trends in Elliptical Galaxies