Mild radial variations of the stellar IMF in the bulge of M31

Abstract

Using new, homogeneous, long-slit spectroscopy in the wavelength range from ~0.35 to ~1micron, we study radial gradients of optical and near-infrared (NIR) IMF-sensitive features along the major axis of the bulge of M31, out to a galacto-centric distance of ~200'' (~800pc). Based on state-of-the-art stellar population synthesis models with varying Na abundance ratio, we fit a number of spectral indices, from different chemical species (including TiO's, Ca, and Na indices), to constrain the low-mass (<0.5M_Sun) end slope (i.e. the fraction of low-mass stars) of the stellar IMF, as a function of galacto-centric distance. Outside a radial distance of ~10'', we infer an IMF similar to a Milky-Way-like distribution, while at small galacto-centric distances, an IMF radial gradient is detected, with a mildly bottom-heavy IMF in the few inner arcsec. We are able to fit Na features (both NaD and NaI8190), without requiring extremely high Na abundance ratios. [Na/Fe] is ~0.4dex for most of the bulge, rising up to ~0.6dex in the innermost radial bins. Our results imply an overall, luminosity-weighted, IMF and mass-to-light ratio for the M31 bulge, consistent with those for a Milky-Way-like distribution, in contrast to results obtained, in general, for most massive early-type galaxies.

arXiv commentaccepted for publication in MNRAS, 22 pages, 16 figures

References in corpus (84)

• On the variation of the Initial Mass Function
• The slope of the black-hole mass versus velocity dispersion correlation
• 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
• Parametric Recovery of Line-of-Sight Velocity Distributions from Absorption-Line Spectra of Galaxies via Penalized Likelihood
• Evolutionary population synthesis: models, analysis of the ingredients and application to high-z galaxies
• The epochs of early-type galaxy formation as a function of environment
• MILES: A Medium resolution INT Library of Empirical Spectra
• A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones
• Improving the full spectrum fitting method: accurate convolution with Gauss-Hermite functions
• CALIFA, the Calar Alto Legacy Integral Field Area survey: I. Survey presentation
• Stellar population models of Lick indices with variable element abundance ratios
• The SAURON project - V. Integral-field emission-line kinematics of 48 elliptical and lenticular galaxies
• The Two Phases of Galaxy Formation
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• The Atlas3D project - XX. Mass-size and mass-sigma distributions of early-type galaxies: bulge fraction drives kinematics, mass-to-light ratio, molecular gas fraction and stellar initial mass function
• Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters
• An Infrared Spectroscopic Sequence of M, L and T Dwarfs
• A systematic variation of the stellar initial mass function in early-type galaxies
• The Indo-U.S. Library of Coude Feed Stellar Spectra
• The Sloan Lens ACS Survey. X. Stellar, Dynamical, and Total Mass Correlations of Massive Early-type Galaxies
• UV-extended E-MILES stellar population models: young components in massive early-type galaxies
• A Substantial Population of Low Mass Stars in Luminous Elliptical Galaxies
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• The Stellar Initial Mass Function in Early-Type Galaxies From Absorption Line Spectroscopy. II. Results
• The initial mass function of early-type galaxies
• A new chemo-evolutionary population synthesis model for early-type galaxies. I: Theoretical basis
• Evolutionary stellar population synthesis with MILES - II. Scaled-solar and α-enhanced models
• Empirical calibration of the near-IR Ca II triplet - I. The stellar library and index definition
• 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
• Higher-order Balmer line indices in alpha/Fe-enhanced stellar population models
• Counting Low-Mass Stars in Integrated Light
• Two-dimensional kinematics of SLACS lenses: III. Mass structure and dynamics of early-type lens galaxies beyond z ~ 0.1
• The long bar as seen by the VVV survey: I. Colour-magnitude diagrams
• Systematic variation of the stellar Initial Mass Function with velocity dispersion in early-type galaxies
• Stellar mass map and dark matter distribution in M31
• Flux-calibrated stellar population models of Lick absorption-line indices with variable element abundance ratios
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. VI. Age and abundance structure of the stellar populations in the central sub-kpc of the Milky Way
• Radial variations in the stellar initial mass function of early-type galaxies
• Empirical calibration of the near-IR CaII triplet - IV. The stellar population synthesis models
• The stellar IMF determined in early-type galaxies from a non-degenerate set of optical line indices
• The Stellar Initial Mass Function in Early-Type Galaxies from Absorption Line Spectroscopy. III. Radial Gradients
• Near-IR line-strengths in elliptical galaxies: evidence for IMF variations?
• The Dawes Review 8: Measuring the Stellar Initial Mass Function
• SDSS-IV MaNGA: The Spatially Resolved Stellar Initial Mass Function in $\sim$400 Early-Type Galaxies
• 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
• An inventory of the stellar initial mass function in early-type galaxies
• The old and heavy bulge of M31 I. Kinematics and stellar populations
• Radial constraints on the Initial Mass Function from TiO features and Wing-Ford band in Early-type Galaxies
• Rejuvenation of spiral bulges
• A giant elliptical galaxy with a lightweight initial mass function
• MUSE observations of M87: radial gradients for the stellar initial-mass function and the abundance of Sodium
• The link between the Star Formation History and [alpha/Fe]
• Stellar and total mass in early-type lensing galaxies
• IMF shape constraints from stellar populations and dynamics from CALIFA
• An optimized H_βindex for disentangling stellar population ages
• The SWELLS survey - V. A Salpeter stellar initial mass function in the bulges of massive spiral galaxies
• IMF and [Na/Fe] abundance ratios from optical and NIR Spectral Features in Early-type Galaxies
• Unveiling dark halos in lensing galaxies
• Galaxy evolution across environments as probed by the ages, stellar metallicities and [alpha/Fe] of central and satellite galaxies
• Evidence for a non-universal stellar initial mass function in low-redshift high-density early-type galaxies
• The Near Infrared NaI Doublet Feature in M Stars
• IMF radial gradients in most massive early-type galaxies
• Eccentric-disk models for the nucleus of M31
• Disk-Bulge-Halo Models for the Andromeda Galaxy
• Variations of the initial mass function in semi-analytical models: implications for the mass assembly and the chemical enrichment of galaxies in the GAEA model
• Skycorr: A general tool for spectroscopic sky subtraction
• MILES extended: Stellar population synthesis models from the optical to the infrared
• The Fornax 3D project: a two-dimensional view of the stellar initial mass function in the massive lenticular galaxy FCC 167
• Strong Gravitational Lensing and the Stellar IMF of Early-type Galaxies
• Sculpting Andromeda -- made-to-measure models for M31's bar and composite bulge: dynamics, stellar and dark matter mass
• Galaxy properties as revealed by MaNGA. I. Constraints on Initial Mass Function and M${}_{\ast }$/L gradients in ellipticals
• Constraining the low-mass end of the Initial Mass Function with Gravitational Lensing
• On the nature of sodium excess objects. I. Data and observed trends
• The Initial Mass Function of Early-type Galaxies: no correlation with [Mg/Fe]
• KINETyS: Constraining spatial variations of the stellar initial mass function in early-type galaxies
• Kinetys II: Constraints on spatial variations of the stellar initial mass function from K-band spectroscopy
• The stellar populations of the central region of M31
• Radial gradients in initial mass function sensitive absorption features in the Coma brightest cluster galaxies
• The initial mass functions of M31 and M32 through far red stellar absorption features
• Andromeda chained to the Box -- Dynamical Models for M31: Bulge & Bar
• On the shape and evolution of a cosmic ray regulated galaxy-wide stellar initial mass function
• Evidence for non-axisymmetry in M31 from wide-field kinematics of stars and gas
• What does (not) drive the variation of the low-mass end of the stellar initial mass function of early-type galaxies

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• sMILES SSPs: A Library of Semi-Empirical MILES Stellar Population Models with Variable [$\alpha$/Fe] Abundances
• INSPIRE: INvestigating Stellar Population In RElics IV. The Initial Mass Function slope in relics
• Variation of the stellar initial mass function in semi-analytical models III: testing the cosmic ray regulated integrated galaxy-wide initial mass function
• CO radial gradients in the bulge of M31
• Puzzling radial gradients of K-band absorption features in the giant elliptical galaxy M87
• Semiresolved Stellar Populations as Distance Indicators
• Downsizing revised: Star formation timescales for elliptical galaxies with an environment-dependent IMF and number of SNIa