THE LOW-MASS STELLAR POPULATION IN L1641: EVIDENCE FOR ENVIRONMENTAL DEPENDENCE OF THE STELLAR INITIAL MASS FUNCTION

Starburst galaxies are currently forming massive stars at prodigious rates. I discuss the star-formation histories and the shape of the initial mass function, with particular emphasis on the high- and on the low-mass end. The classical Salpeter IMF is consistent with constraints from observations of the most massive stars, irrespective of environmental properties. The situation at the low-mass end is less clear: direct star counts in nearby giant H II regions show stars down to ~1 M⊙, whereas dynamical arguments in some starburst galaxies suggest a deficit of such stars.

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The star formation timescale of elliptical galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936636 ◽

2019 ◽

Vol 632 ◽

pp. A110 ◽

Cited By ~ 2

Author(s):

Zhiqiang Yan ◽

Tereza Jerabkova ◽

Pavel Kroupa

Keyword(s):

Star Formation ◽

Stellar Population ◽

Mass Function ◽

Elliptical Galaxies ◽

Initial Mass Function ◽

Different Types ◽

The Galaxy ◽

Stellar Initial Mass Function ◽

Low Mass ◽

Natural Solution

The alpha element to iron peak element ratio, for example [Mg/Fe], is a commonly applied indicator of the galaxy star formation timescale (SFT) since the two groups of elements are mainly produced by different types of supernovae that explode over different timescales. However, it is insufficient to consider only [Mg/Fe] when estimating the SFT. The [Mg/Fe] yield of a stellar population depends on its metallicity. Therefore, it is possible for galaxies with different SFTs and at the same time different total metallicity to have the same [Mg/Fe]. This effect has not been properly taken into consideration in previous studies. In this study, we assume the galaxy-wide stellar initial mass function (gwIMF) to be canonical and invariant. We demonstrate that our computation code reproduces the SFT estimations of previous studies, where only the [Mg/Fe] observational constraint is applied. We then demonstrate that once both metallicity and [Mg/Fe] observations are considered, a more severe “downsizing relation” is required. This means that either low-mass ellipticals have longer SFTs (> 4 Gyr for galaxies with mass below 1010 M⊙) or massive ellipticals have shorter SFTs (≈200 Myr for galaxies more massive than 1011 M⊙) than previously thought. This modification increases the difficulty in reconciling such SFTs with other observational constraints. We show that applying different stellar yield modifications does not relieve this formation timescale problem. The quite unrealistically short SFT required by [Mg/Fe] and total metallicity would be prolonged if a variable stellar gwIMF were assumed. Since a systematically varying gwIMF has been suggested by various observations this could present a natural solution to this problem.

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Variation in the Stellar Initial Mass Function from the Chromospheric Activity of M Dwarfs in Early-type Galaxies

The Astrophysical Journal ◽

10.3847/1538-4357/ac2a30 ◽

2021 ◽

Vol 923 (1) ◽

pp. 43

Author(s):

Pieter van Dokkum ◽

Charlie Conroy

Keyword(s):

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Early Type ◽

M Dwarfs ◽

Low Mass Stars ◽

Chromospheric Activity ◽

Stellar Initial Mass Function ◽

Low Mass ◽

The Imf

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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The Intermediate‐Mass Stellar Population of the Large Magellanic Cloud Cluster NGC 1818 and the Universality of the Stellar Initial Mass Function

The Astrophysical Journal ◽

10.1086/303790 ◽

1997 ◽

Vol 478 (1) ◽

pp. 124-133 ◽

Cited By ~ 42

Author(s):

Deidre A. Hunter ◽

Robert M. Light ◽

Jon A. Holtzman ◽

Roger Lynds ◽

Earl J. O'Neil ◽

...

Keyword(s):

Stellar Population ◽

Mass Function ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Initial Mass Function ◽

Initial Mass ◽

Intermediate Mass ◽

Cloud Cluster ◽

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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LOW-MASS X-RAY BINARIES INDICATE A TOP-HEAVY STELLAR INITIAL MASS FUNCTION IN ULTRACOMPACT DWARF GALAXIES

The Astrophysical Journal ◽

10.1088/0004-637x/747/1/72 ◽

2012 ◽

Vol 747 (1) ◽

pp. 72 ◽

Cited By ~ 68

Author(s):

Jörg Dabringhausen ◽

Pavel Kroupa ◽

Jan Pflamm-Altenburg ◽

Steffen Mieske

Keyword(s):

Dwarf Galaxies ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

X Ray ◽

Stellar Initial Mass Function ◽

Low Mass ◽

X Ray Binaries

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TIMESCALES FOR LOW-MASS STAR FORMATION IN EXTRAGALACTIC ENVIRONMENTS: IMPLICATIONS FOR THE STELLAR INITIAL MASS FUNCTION

The Astrophysical Journal ◽

10.1088/0004-637x/692/1/283 ◽

2009 ◽

Vol 692 (1) ◽

pp. 283-289 ◽

Cited By ~ 9

Author(s):

M. Banerji ◽

S. Viti ◽

D. A. Williams ◽

J. M. C. Rawlings

Keyword(s):

Star Formation ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Mass Star ◽

Stellar Initial Mass Function ◽

Low Mass

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Connection between dynamically derived IMF normalisation and stellar populations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315003373 ◽

2014 ◽

Vol 10 (S311) ◽

pp. 49-52

Author(s):

Richard M. McDermid

Keyword(s):

Stellar Population ◽

Stellar Dynamics ◽

Mass Function ◽

Abundance Ratio ◽

Initial Mass Function ◽

Low Mass Stars ◽

Stellar Initial Mass Function ◽

Low Mass ◽

Future Work ◽

The Imf

AbstractIn this contributed talk I present recent results on the connection between stellar population properties and the normalisation of the stellar initial mass function (IMF) measured using stellar dynamics, based on a large sample of 260 early-type galaxies observed as part of the ATLAS3D project. This measure of the IMF normalisation is found to vary non-uniformly with age- and metallicity-sensitive absorption line strengths. Applying single stellar population models, there are weak but measurable trends of the IMF with age and abundance ratio. Accounting for the dependence of stellar population parameters on velocity dispersion effectively removes these trends, but subsequently introduces a trend with metallicity, such that ‘heavy’ IMFs favour lower metallicities. The correlations are weaker than those found from previous studies directly detecting low-mass stars, suggesting some degree of tension between the different approaches of measuring the IMF. Resolving these discrepancies will be the focus of future work.

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