Extremely alpha-Enriched Globular Clusters in Early-Type Galaxies: A Step towards the Dawn of Stellar Populations?

Abstract

We compare [alpha/Fe], metallicity, and age distributions of globular clusters in elliptical, lenticular, and spiral galaxies, which we derive from Lick line index measurements. We find a large number of globular clusters in elliptical galaxies that reach significantly higher [alpha/Fe] values (>0.5) than any clusters in lenticular and spiral galaxies. Most of these extremely alpha-enriched globular clusters are old (t > 8 Gyr) and cover the metallicity range -1 <~ [Z/H] <~ 0. A comparison with supernova yield models suggests that the progenitor gas clouds of these globular clusters must have been predominantly enriched by massive stars (>~20 M_sol) with little contribution from lower-mass stars. The measured [alpha/Fe] ratios are also consistent with yields of very massive pair-instability supernovae (~130-190 M_sol). Both scenarios imply that the chemical enrichment of the progenitor gas was completed on extremely short timescales of the order of a few Myr. Given the lower [alpha/Fe] average ratios of the diffuse stellar population in early-type galaxies, our results suggest that these extremely alpha-enhanced globular clusters could be members of the very first generation of star clusters formed, and that their formation epochs would predate the formation of the majority of stars in giant early-type galaxies.

6 pages, 3 figures, accepted for publication in the Astrophysical Journal

References in corpus (37)

• Embedded Clusters in Molecular Clouds
• The Nucleosynthetic Signature of Population III
• The epochs of early-type galaxy formation as a function of environment
• Stellar population models of Lick indices with variable element abundance ratios
• Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters
• Detecting Bimodality in Astronomical Datasets
• Dynamical Evolution of the Mass Function of Globular Star Clusters
• Nucleosynthesis in Type Ia Supernovae
• New Insights from HST Studies of Globular Cluster Systems I: Colors, Distances and Specific Frequencies of 28 Elliptical Galaxies
• The ACS Virgo Cluster Survey. I. Introduction to the Survey
• Nucleosynthesis in Type II Supernovae
• Higher-order Balmer line indices in alpha/Fe-enhanced stellar population models
• The Age Distribution of Massive Star Clusters in the Antennae Galaxies
• Globular Cluster Systems I: V-I Color Distributions
• The Ages and Abundances of the M87 Globular Clusters
• Photo-Chemical Evolution of Elliptical Galaxies I. The high-redshift formation scenario
• Explosive Nucleosynthesis in Hypernovae
• Keck Spectroscopy of Globular Clusters around NGC 1399
• The Globular Cluster System of NGC 5128 II. Ages, Metallicities, Kinematics, and Formation
• Integrated Spectroscopy of Bulge Globular Clusters and Fields I. The Data Base and Comparison of Individual Lick Indices in Clusters and Bulge
• Integrated Spectroscopy of Bulge Globular Clusters and Fields. II. Implications for stellar population models and elliptical galaxies
• New Light on the Formation and Evolution of M31 and its Globular Cluster System
• The Age Difference between the Globular Cluster Sub-populations in NGC 4472
• New Insights from HST Studies of Globular Cluster Systems II: Analysis of 29 S0 Systems
• VLT Spectroscopy of Globular Cluster Systems, II. Spectroscopic Ages, Metallicities, and [alpha/Fe] Ratios of Globular Clusters in Early-Type Galaxies
• The Chemical Properties of Milky Way and M31 Globular Clusters: I. A Comparative Study
• Deep Luminosity Functions of Old and Intermediate-Age Globular Clusters in NGC 1316: Evidence for Dynamical Evolution of Second-Generation Globular Clusters
• VLT spectroscopy of NGC3115 globular clusters
• VLT Spectroscopy of Globular Cluster Systems, I. The Photometric and Spectroscopic Dataset
• Old Globular Clusters Masquerading as Young in NGC 4365?
• The Globular Cluster Systems of the Sculptor Group
• Evidence for An Intermediate-Age, Metal-rich Population of Globular Clusters in NGC 4365
• Spectroscopy of Globular Clusters in M81
• Revisiting the Globular Cluster System of the Merger Remnant Elliptical NGC 3610
• Keck Spectroscopy of Globular Clusters in the Sombrero Galaxy
• Self-enrichment in globular clusters. I. An analytic approach
• SNII enrichment and the star cluster mass function

Cited by in corpus (34)

• The ACS Virgo Cluster Survey XV. The Formation Efficiencies of Globular Clusters in Early-Type Galaxies: The Effects of Mass and Environment
• The First Galaxies: Chemical Enrichment, Mixing, and Star Formation
• Star-Forming Galaxies at z~2 and the Formation of the Metal-Rich Globular Cluster Population
• The Ages, Metallicities and Alpha Element Enhancements of Globular Clusters in the Elliptical NGC 5128: A Homogeneous Spectroscopic Study with Gemini/GMOS
• The Kinematics of the Globular Cluster System of NGC 5128 with a New, Large Sample of Radial Velocity Measurements
• Pair-Instability Supernovae at the Epoch of Reionization
• The ACS Fornax Cluster Survey. X. Color Gradients of Globular Cluster Systems in Early-Type Galaxies
• Two formation channels of UCDs in Hickson Compact Groups
• The Age, Metallicity and Alpha-Element Abundance of Galactic Globular Clusters from Single Stellar Population Models
• Dynamical Evolution of Globular Cluster Systems formed in Galaxy Mergers: Deep HST/ACS Imaging of Old and Intermediate-Age Globular Clusters in NGC 3610
• Ages, Metallicities, and [alpha/Fe] ratios of globular clusters in NGC 147, NGC 185, and NGC 205
• Integrated Light Chemical Tagging Analyses of Seven M31 Outer Halo Globular Clusters from the Pan-Andromeda Archaeological Survey
• VLT Spectroscopy of Globular Clusters in Low Surface Brightness Dwarf Galaxies
• The Survey of Centaurus A's Baryonic Structures (SCABS). II. The Extended Globular Cluster System of NGC5128 and its Nearby Environment
• The chemical composition of globular clusters in the Local Group
• The Optical Colors of Giant Elliptical Galaxies and their Metal-Rich Globular Clusters Indicate a Bottom-Heavy Initial Mass Function
• The Formation of Globular Cluster Systems in Massive Elliptical Galaxies: Globular Cluster Multimodality from Radial Variation of Stellar Populations
• Sizes, Half-Mass Densities, and Mass Functions of Star Clusters in the Merger Remnant NGC 1316: Clues to the Fate of Second-Generation Globular Clusters
• Chemical enrichment of stars due to accretion from ISM during the Galaxy's assembly
• New Constraints on a complex relation between globular cluster colors and environment
• Dissolved Massive Metal-Rich Globular Clusters Can Cause the Range of UV Upturn Strengths Found among Early-type Galaxies
• Uncovering the formation of ultra-compact dwarf galaxies by multivariate statistical analysis
• The Next Generation Virgo cluster Survey (NGVS). XXVI. The issues of photometric age and metallicity estimates for globular clusters
• Color-Magnitude Relations within Globular Cluster Systems of Giant Elliptical Galaxies: The Effects of Globular Cluster Mass Loss and the Stellar Initial Mass Function
• Chemical Abundances of Globular Clusters in NGC 5128 (Centaurus A)
• Light-element abundance variations in globular clusters
• On the Precision of Full-spectrum Fitting of Simple Stellar Populations. I. Well-sampled Populations
• A globular cluster in the dwarf galaxy Sextans B
• Deep SDSS Optical Spectroscopy of Distant Halo Stars. III. Chemical analysis of extremely metal-poor stars
• On the Precision of Full-spectrum Fitting of Stellar Populations. III. Identifying Age Spreads
• Old Metal-rich Globular Cluster Populations: Peak Color and Peak Metallicity Trends with Mass of Host Spheroids
• Nonlinear Color-Metallicity Relations of Globular Clusters. XI. Nonlinearity Effect Revealed by NGC 5128 (Centaurus A) and NGC 4594 (Sombrero) Galaxies
• The Next Generation Fornax Survey (NGFS).VIII. A Support Vector Machine Approach for Disentangling Globular Clusters from other Sources
• Origin of the spectacular tidal shells of galaxy NGC474