The puzzling interpretation of NIR indices: The case of NaI2.21

Abstract

We present a detailed study of the Na I line strength index centered in the $K$-band at $22100$, Å (NaI2.21 hereafter) relying on different samples of early-type galaxies. Consistent with previous studies, we find that the observed line strength indices cannot be fit by state-of-art scaled-solar stellar population models, even using our newly developed models in the NIR. The models clearly underestimate the large NaI2.21 values measured for most early-type galaxies. However, we develop a Na-enhanced version of our newly developed models in the NIR, which - together with the effect of a bottom-heavy initial mass function - yield NaI2.21 indices in the range of the observations. Therefore, we suggest a scenario in which the combined effect of [Na/Fe] enhancement and a bottom-heavy initial mass function are mainly responsible for the large NaI2.21 indices observed for most early-type galaxies. To a smaller extent, also [C/Fe] enhancement might contribute to the large observed NaI2.21 values.

arXiv comment13 pages, 4 figures, accepted for publication in MNRAS

References in corpus (54)

• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• Evolutionary tracks and isochrones for low- and intermediate-mass stars: from 0.15 to 7 M_sun, and from Z=0.0004 to 0.03
• Evolutionary population synthesis: models, analysis of the ingredients and application to high-z galaxies
• A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones
• X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very Large Telescope
• Evolutionary Stellar Population Synthesis with MILES. Part I: The Base Models and a New Line Index System
• The Infrared Telescope Facility (IRTF) Spectral Library: Cool Stars
• Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters
• The Stellar Population Histories of Local Early-Type Galaxies. I. Population Parameters
• A large stellar evolution database for population synthesis studies. II. Stellar models and isochrones for an alpha-enhanced metal distribution
• A Substantial Population of Low Mass Stars in Luminous Elliptical Galaxies
• Evolutionary stellar population synthesis with MILES - II. Scaled-solar and α-enhanced models
• Population Synthesis in the Blue IV: Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations
• GALEX UV Color-Magnitude Relations and Evidence for Recent Star Formation in Early-type Galaxies
• An atmospheric radiation model for Cerro Paranal. I. The optical spectral range
• MIUSCAT: extended MILES spectral coverage. I. Stellar populations synthesis models
• SPIDER VIII - Constraints on the Stellar Initial Mass Function of Early-type Galaxies from a Variety of Spectral Features
• Early-Type Galaxy Archeology: Ages, Abundance Ratios, and Effective Temperatures from Full-Spectrum Fitting
• New ATLAS9 And MARCS Model Atmosphere Grids for the Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Counting Low-Mass Stars in Integrated Light
• The SEGUE Stellar Parameter Pipeline. III. Comparison with High-Resolution Spectroscopy of SDSS/SEGUE Field Stars
• Evolutionary synthesis of stellar populations: a modular tool
• Systematic variation of the stellar Initial Mass Function with velocity dispersion in early-type galaxies
• Modeling the color evolution of luminous red galaxies - improvements with empirical stellar spectra
• Stellar populations of early-type galaxies in different environments II. Ages and metallicities
• Absorption-line probes of the prevalence and properties of outflows in present-day star-forming galaxies
• Empirical calibration of the near-IR CaII triplet - IV. The stellar population synthesis models
• Evidence For A Mild Steepening And Bottom-Heavy IMF In Massive Galaxies From Sodium And Titanium-Oxide Indicators
• The stellar IMF determined in early-type galaxies from a non-degenerate set of optical line indices
• On the dependence of spectroscopic indices of early-type galaxies on age, metallicity and velocity dispersion
• The Ages and Metallicities of Early Type Galaxies in the Fornax Cluster
• The SAURON project - XV. Modes of star formation in early-type galaxies and the evolution of the red sequence
• The SINFONI Nearby Elliptical Lens Locator Survey: Discovery of two new low-redshift strong lenses and implications for the initial mass function in giant early-type galaxies
• Center-to-Limb Variation of Solar 3-D Hydrodynamical Simulations
• The X-shooter Spectral Library (XSL): I. DR1. Near-ultraviolet through optical spectra from the first year of the survey
• Flux calibration of medium-resolution spectra from 300 nm to 2500 nm: Model reference spectra and telluric correction
• Radial constraints on the Initial Mass Function from TiO features and Wing-Ford band in Early-type Galaxies
• An Accurate, Easy to Use Abundace Scale for Globular Clusters Based on 2.2um Spectra of Giant Stars
• The peculiar motions of early-type galaxies in two distant regions - V. The Mg-sigma relation, age and metallicity
• A New Approach to the Study of Stellar Populations in Early-Type Galaxies: K-band Spectral Indices and an Application to the Fornax Cluster
• MILES extended: Stellar population synthesis models from the optical to the infrared
• Moderate resolution near-infrared spectroscopy of cool stars: a new K-band library
• Medium Resolution Near Infrared (2.15micron--2.35micron) Spectroscopy of Late-type Main Sequence stars
• Stellar population synthesis models between 2.5 and 5 μm based on the empirical IRTF stellar library
• Differences in carbon and nitrogen abundances between field and cluster early-type galaxies
• The non-universality of the low-mass end of the IMF is robust against the choice of SSP model
• On the nature of sodium excess objects. I. Data and observed trends
• The IMF-sensitive 1.14-micron Na I doublet in early-type galaxies
• Early-type galaxies in the near-infrared: 1.5-2.4\mum spectroscopy
• Evidence for intermediate-age stellar populations in early-type galaxies from K-band spectroscopy
• On the Environmental Dependence of Cluster Galaxy Assembly Timescale
• Single stellar populations in the near-infrared II. Synthesis models
• Near-infrared spectroscopy of stellar populations in nearby spiral galaxies
• Stellar populations of massive elliptical galaxies in very rich clusters

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• A collection of model stellar spectra for spectral types B to early-M
• IMF radial gradients in most massive early-type galaxies
• Modelling simple stellar populations in the near-ultraviolet to near-infrared with the X-shooter Spectral Library (XSL)
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