In 37 massive ETGs, the IMF becomes less bottom-heavy with radius, with average α_IMF falling from 2.16 to 1.74 and IMF gradients dominating M/L variations over stellar population effects.
Systematic variation of the stellar Initial Mass Function with velocity dispersion in early-type galaxies
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abstract
An essential component of galaxy formation theory is the stellar initial mass function (IMF), that describes the parent distribution of stellar mass in star forming regions. We present observational evidence in a sample of early-type galaxies (ETGs) of a tight correlation between central velocity dispersion and the strength of several absorption features sensitive to the presence of low-mass stars. Our sample comprises ~40,000 ETGs from the SPIDER survey (z<0.1). The data, extracted from the Sloan Digital Sky Survey, are combined, rejecting both noisy data, and spectra with contamination from telluric lines, resulting in a set of 18 stacked spectra at high signal-to-noise ratio (S/N> 400 per A). A combined analysis of IMF-sensitive line strengths and spectral fitting is performed with the latest state-of the art population synthesis models (an extended version of the MILES models). A significant trend is found between IMF slope and velocity dispersion, towards an excess of low-mass stars in the most massive galaxies. Although we emphasize that accurate values of the IMF slope will require a detailed analysis of chemical composition (such as [a/Fe] or even individual element abundance ratios), the observed trends suggest that low-mass ETGs are better fit by a Kroupa-like IMF, whereas massive galaxies require bottom-heavy IMFs, exceeding the Salpeter slope at velocity dispersions above 200km/s.
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astro-ph.GA 2years
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UNVERDICTED 2representative citing papers
PCA of H-band IFU pixel spectra decomposes cool stellar populations in NGC 5128 and NGC 5102, identifying M-giant, long-period variable, and carbon star contributions.
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The MASSIVE SURVEY XXI: Local Variations in the Stellar Initial Mass Function of MASSIVE Early-Type Galaxies
In 37 massive ETGs, the IMF becomes less bottom-heavy with radius, with average α_IMF falling from 2.16 to 1.74 and IMF gradients dominating M/L variations over stellar population effects.
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Decomposing cool stellar populations with H-band spectral fluctuations: Long-period variable stars in NGC 5128 and carbon stars in NGC 5102
PCA of H-band IFU pixel spectra decomposes cool stellar populations in NGC 5128 and NGC 5102, identifying M-giant, long-period variable, and carbon star contributions.