Systematic variation of the stellar initial mass function with velocity dispersion in early-type galaxies

Ricciardelli, Elena; Falcón-Barroso, J.; de Carvalho, Reinaldo R.; Vazdekis, A.; de la Rosa, I. G.; La Barbera, Francesco; Ferreras, Ignacio
Referencia bibliográfica

Monthly Notices of the Royal Astronomical Society: Letters, Volume 429, Issue 1, p.L15-L19

Fecha de publicación:
2
2013
Número de autores
7
Número de autores del IAC
3
Número de citas
205
Número de citas referidas
192
Descripción
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 Spheroids Panchromatic Investigation in Different Environmental Regions 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 Å-1). 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 [α/Fe] or even individual element abundance ratios), the observed trends suggest that low-mass ETGs are better fitted by a Kroupa-like IMF, whereas massive galaxies require bottom-heavy IMFs, exceeding the Salpeter slope at σ ≳ 200 km s-1.
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