Seeing Red in M32: Constraints on the Stellar Content from Near- and Mid-Infrared Observations and Applications for Studies of More Distant Galaxies

Abstract

The properties of asymptotic giant branch (AGB) stars in the Local Group galaxy M32 are investigated using ground and space-based observations that span the 1 - 8um wavelength interval, with the goal of demonstrating the utility of infrared observations as probes of stellar content. Comparisons with isochrones indicate that the brightest resolved stars in M32 have ages of a few Gyr, and are younger on average than AGB stars with the same intrinsic brightness in the outer disk of M31. Accounting for stellar variability is shown to be essential for modelling AGB luminosity functions (LFs). Model LFs that assume the star-forming history measured by Monachesi et al. (2012, ApJ, 745, 97) and the variability properties of Galactic AGB stars match both the K and [5.8] LFs of M32. Models also suggest that the slope of the [5.8] LF between M_[5.8] = -8.5 and --10.0 is sensitive to the mix of stellar ages, and a sizeable fraction of the stars in M32 must have an age older than 7 Gyr in order to match the [5.8] LF. The structural properties of M32 in the infrared are also investigated. The effective radii that are computed from near-infrared and mid-infrared isophotes are similar to those measured at visible wavelengths, suggesting that the stellar content of M32 is well-mixed. However, isophotes at radii > 16 arcsec (> 60 parsecs) in the near and mid-infrared are flatter than those at visible wavelengths. The coefficient of the fourth-order cosine term in the fourier expansion of isophotes changes from `boxy' values at r < 16 arcsec to `disky' values at r > 48 arcsec in [3.6] and [4.5]. The mid-infrared colors near the center of M32 do not vary systematically with radius, providing evidence of a well-mixed stellar content in this part of the galaxy.

arXiv commentTo appear in The Astrophysical Journal

References in corpus (54)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
• Evolutionary population synthesis: models, analysis of the ingredients and application to high-z galaxies
• Evolution of asymptotic giant branch stars II. Optical to far-infrared isochrones with improved TP-AGB models
• The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 microns Using GLIMPSE Data
• Spitzer Survey of the Large Magellanic Cloud, Surveying the Agents of a Galaxy's Evolution (SAGE) I: Overview and Initial Results
• Absolute Calibration of the Infrared Array Camera on the Spitzer Space Telescope
• HI in Local Group Dwarf Galaxies and Stripping by the Galactic Halo
• The Galactic disk mass-budget : I. stellar mass-function and density
• The Panchromatic Hubble Andromeda Treasury
• The ACS Nearby Galaxy Survey Treasury IX. Constraining asymptotic giant branch evolution with old metal-poor galaxies
• Number Counts At 3 < lambda < 10 um From the Spitzer Space Telescope
• M32+/-1
• Spitzer/MIPS Infrared Imaging of M31: Further Evidence for a Spiral/Ring Composite Structure
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA) II: Dust and Gas in Andromeda
• Tidal Interaction of M32 and NGC 205 with M31: Surface Photometry and Numerical Simulations
• The mid- and far-infrared colours of AGB and post-AGB stars
• An almost head-on collision as the origin of two off-centre rings in the Andromeda galaxy
• A new formation model for M32: A threshed early-type spiral?
• An Imaging Survey of Early-Type Barred Galaxies
• Hubble Space Telescope Observations of M32: The Color-Magnitude Diagram
• Evidence for an outer disk in the Prototype `Compact Elliptical' Galaxy M32
• Does M31 result from an ancient major merger?
• New Light on the Formation and Evolution of M31 and its Globular Cluster System
• Near Infrared spectroscopy of post-starburst galaxies: a limited impact of TP-AGB stars on galaxy SEDs
• Dynamical Mass Estimates for the Halo of M31 from Keck Spectroscopy
• The Contribution of TP-AGB and RHeB Stars to the Near-IR Luminosity of Local Galaxies: Implications for Stellar Mass Measurements of High Redshift Galaxies
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA). I: Global far-infrared and sub-mm morphology
• Stellar populations of early-type galaxies in different environments III. Line-strength gradients
• Evolution of Thermally Pulsing Asymptotic Giant Branch Stars IV. Constraining Mass-Loss & Lifetimes of Low Mass, Low Metallicity AGB Stars
• The Star Formation History and Dust Content in the Far Outer Disc of M31
• The M33 Variable Star Population Revealed by Spitzer
• The Chemical Properties of Milky Way and M31 Globular Clusters: II. Stellar Population Model Predictions
• Balmer and Metal Absorption Feature Gradients in M32
• Radial Age and Metal Abundance Gradients in the Stellar Content of M32
• Observational Constraints on Red and Blue Helium Burning Sequences
• An analysis of the composite stellar population in M32
• The Star Formation History of M32
• Shaken, Not Stirred: The Disrupted Disk of the Starburst Galaxy NGC 253
• Molecular gas in the inner 0.7kpc-radius ring of M31
• The Recent Stellar Archeology of M31 - The Nearest Red Disk Galaxy
• A point source survey of M31 with the Spitzer Space Telescope
• An Ancient Metal-Poor Population in M32, and Halo Satellite Accretion in M31, Identified by RR Lyrae Stars
• The Evolved Red Stellar Content of M32
• Probing the Central Regions of Nearby Compact Elliptical Galaxies
• The Asymptotic Giant Branch and the Tip of the Red Giant Branch as Probes of Star Formation History: The Nearby Dwarf Irregular Galaxy KKH 98
• The Peak Brightness and Spatial Distribution of AGB Stars Near the Nucleus of M32
• The Brightest Stars in M32: Comparing Predictions from Spectra with the Resolved Stellar Content
• Young Stars at the Edge: Stellar Clustering in the Outer Regions of the M33 Disk
• A Large Group of Asymptotic Giant Branch Stars in the Disk of M31: A Missing Piece of the Puzzle?
• The Open Cluster NGC 2437 (Messier 46)
• Photometric Variability Among the Brightest Asymptotic Giant Branch Stars Near the Center of M32
• Identifying Bright Stars in Crowded Environments Using Velocity Dispersion Measurements, and an Application to the Center of M32

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• An Infrared Census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS). IV. Discovery of High-Redshift AGB Analogs
• Carbon Stars in the Satellites and Halo of M31
• The Star-Forming Histories of the Nucleus, Bulge, and Inner Disk of NGC 5102: Clues to the Evolution of a Nearby Lenticular Galaxy
• A Spitzer Space Telescope survey of extreme Asymptotic Giant Branch stars in M32
• Raven and the Center of Maffei 1: Multi-Object Adaptive Optics Observations of the Center of a Nearby Elliptical Galaxy and the Detection of an Intermediate Age Population
• Cluster Glimpses with Raven: AO Corrected Near and Mid-Infrared Images of Glimpse C01 and Glimpse C02
• The Lop-sided Spiral Galaxy NGC 247: Clues to a Possible Interaction with NGC 253
• Infrared variable stars in the compact elliptical galaxy M32
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