VARIATIONS OF THE STELLAR INITIAL MASS FUNCTION IN THE PROGENITORS OF MASSIVE EARLY-TYPE GALAXIES AND IN EXTREME STARBURST ENVIRONMENTS

Abstract Mass measurements and absorption-line studies indicate that the stellar initial mass function (IMF) is bottom-heavy in the central regions of many early-type galaxies, with an excess of low-mass stars compared to the IMF of the Milky Way. Here we test this hypothesis using a method that is independent of previous techniques. Low-mass stars have strong chromospheric activity characterized by nonthermal emission at short wavelengths. Approximately half of the UV flux of M dwarfs is contained in the λ1215.7 Lyα line, and we show that the total Lyα emission of an early-type galaxy is a sensitive probe of the IMF with a factor of ∼2 flux variation in response to plausible variations in the number of low-mass stars. We use the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure the Lyα line in the centers of the massive early-type galaxies NGC 1407 and NGC 2695. We detect Lyα emission in both galaxies and demonstrate that it originates in stars. We find that the Lyα to i-band flux ratio is a factor of 2.0 ± 0.4 higher in NGC 1407 than in NGC 2695, in agreement with the difference in their IMFs as previously determined from gravity-sensitive optical absorption lines. Although a larger sample of galaxies is required for definitive answers, these initial results support the hypothesis that the IMF is not universal but varies with environment.

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IMF variations in unresolved stellar populations: Challenges

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316004853 ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 193-194

Author(s):

Ignacio Ferreras ◽

Francesco La Barbera ◽

Alexandre Vazdekis

Keyword(s):

Stellar Populations ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Spectral Features ◽

Early Type ◽

Stellar Initial Mass Function

AbstractThis talk focuses on the challenges facing the recent discovery of variations of the stellar initial mass function in massive early-type galaxies, with special emphasis on the constraints via gravity-sensitive spectral features.

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KINETyS: Constraining spatial variations of the stellar initial mass function in early-type galaxies ★

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stx464 ◽

2017 ◽

Cited By ~ 11

Author(s):

Padraig D. Alton ◽

Russell J. Smith ◽

John R. Lucey

Keyword(s):

Mass Function ◽

Spatial Variations ◽

Initial Mass Function ◽

Initial Mass ◽

Early Type ◽

Stellar Initial Mass Function

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Stellar initial mass function variation in massive early-type galaxies: the potential role of the deuterium abundance

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2679 ◽

2020 ◽

Vol 498 (3) ◽

pp. 4051-4059 ◽

Cited By ~ 1

Author(s):

Timothy A Davis ◽

Freeke van de Voort

Keyword(s):

Mass Loss ◽

Cosmic Time ◽

Mass Function ◽

Stellar Mass ◽

Initial Mass Function ◽

Initial Mass ◽

Early Type ◽

Root Cause ◽

Stellar Initial Mass Function ◽

Low Mass

ABSTRACT The observed stellar initial mass function (IMF) appears to vary, becoming bottom-heavy in the centres of the most massive, metal-rich early-type galaxies. It is still unclear what physical processes might cause this IMF variation. In this paper, we demonstrate that the abundance of deuterium in the birth clouds of forming stars may be important in setting the IMF. We use models of disc accretion on to low-mass protostars to show that those forming from deuterium-poor gas are expected to have zero-age main-sequence masses significantly lower than those forming from primordial (high deuterium fraction) material. This deuterium abundance effect depends on stellar mass in our simple models, such that the resulting IMF would become bottom-heavy – as seen in observations. Stellar mass loss is entirely deuterium free and is important in fuelling star formation across cosmic time. Using the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulation we show that stellar mass-loss-induced deuterium variations are strongest in the same regions where IMF variations are observed: at the centres of the most massive, metal-rich, passive galaxies. While our analysis cannot prove that the deuterium abundance is the root cause of the observed IMF variation, it sets the stage for future theoretical and observational attempts to study this possibility.

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