Radial Trends in IMF-Sensitive Absorption Features in Two Early-Type Galaxies: Evidence for Abundance-Driven Gradients

Abstract

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 8000-10,000 Å. We present spatially resolved measurements of the dwarf-sensitive spectral indices NaI (8190 Å) and Wing-Ford FeH (9915 Å), as well as indices for species of H, C${}_2$, 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 NaI index and the CN${}_1$ index at 4160 Å exhibit significantly steeper gradients, with a break at $r\sim 0.1r_{\mathrm{eff}}$ ($r\sim 300$ pc). Inside this radius NaI strength increases sharply toward the galaxy center, consistent with a rapid central rise in [Na/Fe]. In contrast, the ratio of FeH to Fe index strength decreases toward the galaxy center. This behavior cannot be reproduced by a steepening IMF inside $0.1r_{\mathrm{eff}}$ if the IMF is a single power law. While gradients in the mass function above $\sim 0.4M_{\odot }$ may occur, exceptional care is required to disentangle these IMF variations from the extreme variations in individual element abundances near the galaxies' centers.

Accepted for publication in ApJ. Updates from v1 include an expanded comparison of measured index strengths to SPS models. 20 page body + 7 page appendix + references. Includes 25 figures

References in corpus (37)

• Star Formation in AEGIS Field Galaxies since z=1.1 : The Dominance of Gradually Declining Star Formation, and the Main Sequence of Star-Forming Galaxies
• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• 3D-HST+CANDELS: The Evolution of the Galaxy Size-Mass Distribution since $z=3$
• Galactic chemical evolution: Carbon through Zinc
• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• A systematic variation of the stellar initial mass function in early-type galaxies
• The Atlas3D Project - XXX. Star formation histories and stellar population scaling relations of early-type galaxies
• The Structure & Dynamics of Massive Early-type Galaxies: On Homology, Isothermality and Isotropy inside one Effective Radius
• Population Synthesis in the Blue IV: Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations
• The Relation Between SFR and Stellar Mass for Galaxies at 3.5 $\le z\le$ 6.5 in CANDELS
• The Universal Relation of Galactic Chemical Evolution: The Origin of the Mass-Metallicity Relation
• Very low metallicity massive star models: Pre-SN evolution and primary nitrogen production
• Oxygen, Sodium, Magnesium and Aluminium as tracers of the Galactic Bulge Formation
• The SAURON project - VI. Line strength maps of 48 elliptical and lenticular galaxies
• Radial variations in the stellar initial mass function of early-type galaxies
• Origin of multiple stellar populations in globular clusters and their helium enrichment
• Spatially resolved spectroscopy of early-type galaxies over a range in mass
• Measuring Ages and Elemental Abundances from Unresolved Stellar Populations: Fe, Mg, C, N, and Ca
• Light, Alpha, and Fe-Peak Element Abundances in the Galactic Bulge
• Variations of the stellar initial mass function in the progenitors of massive early-type galaxies and in extreme starburst environments
• Ages and Abundances of Red Sequence Galaxies as a Function of LINER Emission Line Strength
• The stellar population histories of early-type galaxies. III. The Coma Cluster
• 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
• The stellar initial mass function of early type galaxies from low to high stellar velocity dispersion: homogeneous analysis of ATLAS${}^{3D}$ and Sloan Lens ACS galaxies
• Radial constraints on the Initial Mass Function from TiO features and Wing-Ford band in Early-type Galaxies
• The SAURON Project - XIV. No escape from V${}_{\mathrm{esc}}$: a global and local parameter in early-type galaxy evolution
• P-MaNGA: Full spectral fitting and stellar population maps from prototype observations
• The SLUGGS survey: Exploring the metallicity gradients of nearby early-type galaxies to large radii
• The initial mass function of a massive relic galaxy
• The self-enrichment scenario in intermediate metallicity globular clusters
• Skycorr: A general tool for spectroscopic sky subtraction
• AGB Sodium Abundances in the Globular Cluster 47 Tucanae (NGC 104)
• Connection between dynamically derived IMF normalisation and stellar population parameters
• The IMF-sensitive 1.14-micron Na I doublet in early-type galaxies
• The initial mass functions of M31 and M32 through far red stellar absorption features
• Composite Stellar Populations and Element by Element Abundances in the Milky Way Bulge and Elliptical Galaxies

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• Detection of Enhanced Central Mass-to-Light Ratios in Low-Mass Early-Type Galaxies: Evidence for Black Holes?
• Calibrated, cosmological hydrodynamical simulations with variable IMFs III: Spatially-resolved properties and evolution
• The SLUGGS Survey: The Inner Dark Matter Density Slope of the Massive Elliptical Galaxy NGC 1407
• Stellar dynamics in the strong-lensing central galaxy of Abell 1201: A low stellar mass-to-light ratio, a large central compact mass, and a standard dark matter halo
• Evidence of a Bottom-heavy Initial Mass Function in Massive Early-type Galaxies from Near-infrared Metal Lines
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