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The Stellar Initial Mass Function in Early-Type Galaxies From Absorption Line Spectroscopy. I. Data and Empirical Trends
Cosmology and Nongalactic Astrophysics · Submitted 29 May 2012
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim These trends are consistent with a varying IMF, such that galaxies with deeper potential wells have more dwarf-enriched mass functions.
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The abstract, sentence by sentence
The strength of gravity-sensitive absorption lines in the integrated light of old stellar populations is one of the few direct probes of the stellar initial mass function (IMF) outside of the Milky Way. Owing to the advent of fully depleted CCDs with little or no fringing it has recently become possible to obtain accurate measurements of these features. Here we present spectra covering the wavelength ranges 0.35 - 0.55 micron and 0.72 - 1.03 micron for the bulge of M31 and 34 early-type galaxies from the SAURON sample, obtained with the Low Resolution Imaging Spectrometer on Keck. The signal-to-noise ratio is >200 per Angstrom out to 1 micron, which is sufficient to measure gravity-sensitive features for individual galaxies and to determine how they depend on other properties of the galaxies. Combining the new data with previously obtained spectra for globular clusters in M31 and the most massive elliptical galaxies in the Virgo cluster we find that the dwarf-sensitive Na I doublet and the FeH Wing-Ford band increase systematically with velocity dispersion, while the giant-sensitive Ca II triplet decreases with dispersion. These trends are consistent with a varying IMF, such that galaxies with deeper potential wells have more dwarf-enriched mass functions. In a companion paper (Conroy & van Dokkum 2012) we use a comprehensive stellar population synthesis model to demonstrate that IMF effects can be separated from age and abundance variations and quantify the IMF variation among early-type galaxies.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The strength of gravity-sensitive absorption lines in the integrated light of old stellar populations is one of the few direct probes of the stellar initial mass function (IMF) outside of the Milky Way. | background 1.00 | 0.05 | 0.03 | asserted 0.99 |
| s1 | Owing to the advent of fully depleted CCDs with little or no fringing it has recently become possible to obtain accurate measurements of these features. | background 0.84 | 0.07 | 0.01 | asserted 0.83 |
| s2 | Here we present spectra covering the wavelength ranges 0.35 - 0.55 micron and 0.72 - 1.03 micron for the bulge of M31 and 34 early-type galaxies from the SAURON sample, obtained with the Low Resolution Imaging Spectrometer on Keck. | method 0.79 | 0.96 | 0.02 | asserted 0.99 |
| s3 | The signal-to-noise ratio is >200 per Angstrom out to 1 micron, which is sufficient to measure gravity-sensitive features for individual galaxies and to determine how they depend on other properties of the galaxies. | method 0.76 | 0.93 | 0.03 | asserted 0.97 |
| s4 | Combining the new data with previously obtained spectra for globular clusters in M31 and the most massive elliptical galaxies in the Virgo cluster we find that the dwarf-sensitive Na I doublet and the FeH Wing-Ford band increase systematically with velocity dispersion, while the giant-sensitive Ca II triplet decreases with dispersion. | result 1.00 | 0.95 | 0.45 | asserted 1.00 |
| s5 | These trends are consistent with a varying IMF, such that galaxies with deeper potential wells have more dwarf-enriched mass functions. | interpretation 1.00 | 0.71 | 0.85 | hedged possibility 1.00 |
| s6 | In a companion paper (Conroy & van Dokkum 2012) we use a comprehensive stellar population synthesis model to demonstrate that IMF effects can be separated from age and abundance variations and quantify the IMF variation among early-type galaxies. | future work 0.86 | 0.68 | 0.06 | asserted 1.00 |
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Original abstract
The strength of gravity-sensitive absorption lines in the integrated light of old stellar populations is one of the few direct probes of the stellar initial mass function (IMF) outside of the Milky Way. Owing to the advent of fully depleted CCDs with little or no fringing it has recently become possible to obtain accurate measurements of these features. Here we present spectra covering the wavelength ranges 0.35 - 0.55 micron and 0.72 - 1.03 micron for the bulge of M31 and 34 early-type galaxies from the SAURON sample, obtained with the Low Resolution Imaging Spectrometer on Keck. The signal-to-noise ratio is >200 per Angstrom out to 1 micron, which is sufficient to measure gravity-sensitive features for individual galaxies and to determine how they depend on other properties of the galaxies. Combining the new data with previously obtained spectra for globular clusters in M31 and the most massive elliptical galaxies in the Virgo cluster we find that the dwarf-sensitive Na I doublet and the FeH Wing-Ford band increase systematically with velocity dispersion, while the giant-sensitive Ca II triplet decreases with dispersion. These trends are consistent with a varying IMF, such that galaxies with deeper potential wells have more dwarf-enriched mass functions. In a companion paper (Conroy & van Dokkum 2012) we use a comprehensive stellar population synthesis model to demonstrate that IMF effects can be separated from age and abundance variations and quantify the IMF variation among early-type galaxies.
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There is some strong evidence that giant elliptical galaxies grow their extended stellar haloes slowly, through accretion, around a dense, compact core [ref] .
Isolated ellipticals and their globular cluster systems I: Washington photometry of NGC 3585 and NGC 5812 · Introduction · 0.81
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