The Initial Mass Function of a Massive Star‐forming Region W51

ABSTRACT We study the effects of the integrated galactic initial mass function (IGIMF) and dust evolution on the abundance patterns of high redshift starburst galaxies. In our chemical models, the rapid collapse of gas clouds triggers an intense and rapid star formation episode, which lasts until the onset of a galactic wind, powered by the thermal energy injected by stellar winds and supernova explosions. Our models follow the evolution of several chemical elements (C, N, α-elements, and Fe) both in the gas and dust phases. We test different values of β, the slope of the embedded cluster mass function for the IGIMF, where lower β values imply a more top-heavy initial mass function (IMF). The computed abundances are compared to high-quality abundance measurements obtained in lensed galaxies and from composite spectra in large samples of star-forming galaxies in the redshift range 2 ≲ z ≲ 3. The adoption of the IGIMF causes a sensible increase of the rate of star formation with respect to a standard Salpeter IMF, with a strong impact on chemical evolution. We find that in order to reproduce the observed abundance patterns in these galaxies, either we need a very top-heavy IGIMF (β < 2) or large amounts of dust. In particular, if dust is important, the IGIMF should have β ≥ 2, which means an IMF slightly more top-heavy than the Salpeter one. The evolution of the dust mass with time for galaxies of different mass and IMF is also computed, highlighting that the dust amount increases with a top-heavier IGIMF.

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The sub-solar initial mass function in the Large Magellanic Cloud

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308028524 ◽

2008 ◽

Vol 4 (S256) ◽

pp. 250-255

Author(s):

Dimitrios A. Gouliermis

Keyword(s):

Star Formation ◽

Hubble Space Telescope ◽

Mass Function ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Magellanic Clouds ◽

Initial Mass Function ◽

Initial Mass ◽

Star Forming ◽

Advanced Camera For Surveys

AbstractThe Magellanic Clouds offer a unique variety of star forming regions seen as bright nebulae of ionized gas, related to bright young stellar associations. Nowadays, observations with the high resolving efficiency of the Hubble Space Telescope allow the detection of the faintest infant stars, and a more complete picture of clustered star formation in our dwarf neighbors has emerged. I present results from our studies of the Magellanic Clouds, with emphasis in the young low-mass pre-main sequence populations. Our data include imaging with the Advanced Camera for Surveys of the association LH 95 in the Large Magellanic Cloud, the deepest observations ever taken with HST of this galaxy. I discuss our findings in terms of the initial mass function, which we constructed with an unprecedented completeness down to the sub-solar regime, as the outcome of star formation in the low-metallicity environment of the LMC.

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Impact of metallicity and star formation rate on the time-dependent, galaxy-wide stellar initial mass function

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833055 ◽

2018 ◽

Vol 620 ◽

pp. A39 ◽

Cited By ~ 32

Author(s):

T. Jeřábková ◽

A. Hasani Zonoozi ◽

P. Kroupa ◽

G. Beccari ◽

Z. Yan ◽

...

Keyword(s):

Star Formation ◽

Dwarf Galaxies ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Probability Density Distribution ◽

Star Forming ◽

The Galaxy ◽

Stellar Initial Mass Function ◽

Stellar Masses

The stellar initial mass function (IMF) is commonly assumed to be an invariant probability density distribution function of initial stellar masses. These initial stellar masses are generally represented by the canonical IMF, which is defined as the result of one star formation event in an embedded cluster. As a consequence, the galaxy-wide IMF (gwIMF) should also be invariant and of the same form as the canonical IMF; gwIMF is defined as the sum of the IMFs of all star-forming regions in which embedded clusters form and spawn the galactic field population of the galaxy. Recent observational and theoretical results challenge the hypothesis that the gwIMF is invariant. In order to study the possible reasons for this variation, it is useful to relate the observed IMF to the gwIMF. Starting with the IMF determined in resolved star clusters, we apply the IGIMF-theory to calculate a comprehensive grid of gwIMF models for metallicities, [Fe/H] ∈ (−3, 1), and galaxy-wide star formation rates (SFRs), SFR ∈ (10−5, 105) M⊙ yr−1. For a galaxy with metallicity [Fe/H] < 0 and SFR > 1 M⊙ yr−1, which is a common condition in the early Universe, we find that the gwIMF is both bottom light (relatively fewer low-mass stars) and top heavy (more massive stars), when compared to the canonical IMF. For a SFR < 1 M⊙ yr−1 the gwIMF becomes top light regardless of the metallicity. For metallicities [Fe/H] > 0 the gwIMF can become bottom heavy regardless of the SFR. The IGIMF models predict that massive elliptical galaxies should have formed with a gwIMF that is top heavy within the first few hundred Myr of the life of the galaxy and that it evolves into a bottom heavy gwIMF in the metal-enriched galactic centre. Using the gwIMF grids, we study the SFR−Hα relation and its dependency on metallicity and the SFR. We also study the correction factors to the Kennicutt SFRK − Hα relation and provide new fitting functions. Late-type dwarf galaxies show significantly higher SFRs with respect to Kennicutt SFRs, while star-forming massive galaxies have significantly lower SFRs than hitherto thought. This has implications for gas-consumption timescales and for the main sequence of galaxies. We explicitly discuss Leo P and ultra-faint dwarf galaxies.

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The massive star-forming region Cygnus OB2

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309992055 ◽

2009 ◽

Vol 5 (S266) ◽

pp. 551-554

Author(s):

N. J. Wright ◽

J. J. Drake

Keyword(s):

Massive Star ◽

Near Infrared ◽

Protoplanetary Disks ◽

Mass Function ◽

Initial Mass Function ◽

Point Sources ◽

Older Population ◽

X Ray ◽

Ob Stars ◽

Star Forming

AbstractWe present results from a catalogue of 1696 X-ray point sources detected in the massive star-forming region Cygnus OB2, the majority of which have optical or near-infrared associations. We derive ages of 3.5 and 5.25 Myr for the stellar populations in our two fields, in agreement with recent studies that suggest that the central 1–3 Myr-old OB association is surrounded and contaminated by an older population with an age of 5–10 Myr. The fraction of sources with protoplanetary disks, as traced by K-band excesses, is unusually low. Although this has previously been interpreted as due to the influence of the large number of OB stars in Cyg OB2, contamination from an older population of stars in the region could also be responsible. An initial mass function is derived and found to have a slope of Γ = −1.27, in agreement with the canonical value. Finally, we introduce the recently approved Chandra Cygnus OB2 Legacy Survey that will image a 1 square degree area of the Cygnus OB2 association to a depth of 120~ks, likely detecting ~ 10 000 stellar X-ray sources.

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The initial mass function and history of the star-formation rate in star-forming complexes in galaxies

Astronomy Reports ◽

10.1134/1.1822973 ◽

2004 ◽

Vol 48 (11) ◽

pp. 909-920

Author(s):

F. Kh. Sakhibov ◽

M. A. Smirnov

Keyword(s):

Star Formation ◽

Star Formation Rate ◽

Formation Rate ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Star Forming ◽

History Of

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The massive star Initial Mass function

Symposium - International Astronomical Union ◽

10.1017/s007418090021303x ◽

2003 ◽

Vol 212 ◽

pp. 642-651 ◽

Cited By ~ 3

Author(s):

Daniel Schaerer

Keyword(s):

Massive Star ◽

Current Knowledge ◽

Star Clusters ◽

Mass Function ◽

Initial Mass Function ◽

H Ii Regions ◽

Star Forming ◽

Star Forming Regions ◽

Super Star Clusters ◽

The Imf

We review our current knowledge on the IMF in nearby environments, massive star forming regions, super star clusters, starbursts and alike objects from studies of integrated light, and discuss the various techniques used to constrain the IMF. In most cases, including UV-optical studies of stellar features and optical-IR analysis of nebular emission, the data is found to be compatible with a ‘universal’ Salpeter-like IMF with a high upper mass cut-off over a large metallicity range. In contrast, near-IR observations of nuclear starbursts and LIRG show indications of a lowerMupand/or a steeper IMF slope, for which no alternate explanation has yet been found. Also, dynamical mass measurements of seven super star clusters provide so far no simple picture of the IMF. Finally, we present recent results of a direct stellar probe of the upper end of the IMF in metal-rich H ii regions, showing no deficiency of massive stars at high metallicity, and determining a lower limit ofMup≳ 60 – 90 M⊙.

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The Variation of the Initial Mass Function in Clusters

Symposium - International Astronomical Union ◽

10.1017/s0074180900241648 ◽

2004 ◽

Vol 221 ◽

pp. 237-246

Author(s):

K. L. Luhman

Keyword(s):

Star Formation ◽

Brown Dwarfs ◽

Mass Function ◽

Open Clusters ◽

Initial Mass Function ◽

Initial Mass ◽

Star Forming ◽

Star Forming Regions

I review recent measurements of the initial mass function of stars and brown dwarfs in star-forming regions and open clusters and summarize the implications of these data for theories of star formation.

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