Seeing red in M32 : constraints on the stellar content from near- and mid-infrared observations and applications for studies of more distant galaxies

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DOIResolve DOI: http://doi.org/10.1088/0004-637X/791/1/66
AuthorSearch for:
TypeArticle
Journal titleThe Astrophysical Journal
ISSN0004-637X
Volume791
Issue1
Article number66
Pages123; # of pages: 23
Subjectgalaxies: dwarf; galaxies: evolution; galaxies: individual (M32); Local Group
AbstractThe properties of asymptotic giant branch (AGB) stars in the Local Group galaxy M32 are investigated using ground- and space-based observations that span the 1-8 μm 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 gigayears 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 modeling AGB luminosity functions (LFs). Model LFs that assume the star-forming history measured by Monachesi et al. 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″ (>60 pc) 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″ to "disky" values at r > 48″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.
Publication date
LanguageEnglish
AffiliationNational Science Infrastructure; National Research Council Canada
Peer reviewedYes
NPARC number21272866
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Record identifiera0921156-1ef7-4882-857d-190368ed9f12
Record created2014-12-03
Record modified2016-07-18
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