Evidence of a bottom-heavy initial mass function in massive early-type galaxies from near-infrared metal lines

Lagattuta, David J., Mould, Jeremy R., Forbes, Duncan A., Monson, Andrew J., Pastorello, Nicola and Persson, S. Eric 2017, Evidence of a bottom-heavy initial mass function in massive early-type galaxies from near-infrared metal lines, Astrophysical Journal, vol. 846, no. 2, doi: 10.3847/1538-4357/aa8563.

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Title Evidence of a bottom-heavy initial mass function in massive early-type galaxies from near-infrared metal lines
Author(s) Lagattuta, David J.
Mould, Jeremy R.
Forbes, Duncan A.
Monson, Andrew J.
Pastorello, NicolaORCID iD for Pastorello, Nicola orcid.org/0000-0003-3032-3866
Persson, S. Eric
Journal name Astrophysical Journal
Volume number 846
Issue number 2
Total pages 16
Publisher Institute of Physics Publishing
Place of publication Philadelphia, Pa.
Publication date 2017-09-10
ISSN 0004-637X
Keyword(s) Science & Technology
Physical Sciences
Astronomy & Astrophysics
galaxies: elliptical and lenticular, cD
galaxies: evolution
galaxies: formation
galaxies: stellar content
stars: luminosity function, mass
Summary We present new evidence for a variable stellar initial mass function (IMF) in massive early-type galaxies, using high-resolution, near-infrared spectroscopy from the Folded-port InfraRed Echellette spectrograph (FIRE) on the Magellan Baade Telescope at Las Campanas Observatory. In this pilot study, we observe several gravity-sensitive metal lines between 1.1 and 1.3 μm in eight highly luminous () nearby galaxies. Thanks to the broad wavelength coverage of FIRE, we are also able to observe the Ca ii triplet feature, which helps with our analysis. After measuring the equivalent widths (EWs) of these lines, we notice mild to moderate trends between EW and central velocity dispersion (σ), with some species (K i, Na i, Mn i) showing a positive EW-σ correlation and others (Mg i, Ca ii, Fe i) a negative one. To minimize the effects of metallicity, we measure the ratio R = [EW(K i)/EW(Mg i)], finding a significant systematic increase in this ratio with respect to σ. We then probe for variations in the IMF by comparing the measured line ratios to the values expected in several IMF models. Overall, we find that low-mass galaxies ( km s -1 ) favor a Chabrier IMF, while high-mass galaxies ( km s -1 ) are better described with a steeper (dwarf-rich) IMF slope. While we note that our galaxy sample is small and may suffer from selection effects, these initial results are still promising. A larger sample of galaxies will therefore provide an even clearer picture of IMF trends in this regime.
Language eng
DOI 10.3847/1538-4357/aa8563
Field of Research 0201 Astronomical And Space Sciences
0305 Organic Chemistry
0306 Physical Chemistry (Incl. Structural)
HERDC Research category C1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Copyright notice ©2017, American Astronomical Society
Persistent URL http://hdl.handle.net/10536/DRO/DU:30106280

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