The Initial Mass Function of the Massive Star‐forming Region NGC 3603 from Near‐Infrared Adaptive Optics Observations

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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High-contrast and resolution near-infrared photometry of the core of R136

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab388 ◽

2021 ◽

Vol 503 (1) ◽

pp. 292-311

Author(s):

Zeinab Khorrami ◽

Maud Langlois ◽

Paul C Clark ◽

Farrokh Vakili ◽

Anne S M Buckner ◽

...

Keyword(s):

Adaptive Optics ◽

Near Infrared ◽

Outer Region ◽

Mass Range ◽

Mass Function ◽

Large Magellanic Cloud ◽

Star Forming ◽

The Core ◽

Very Large Telescope ◽

30 Doradus

ABSTRACT We present the sharpest and deepest near-infrared photometric analysis of the core of R136, a newly formed massive star cluster at the centre of the 30 Doradus star-forming region in the Large Magellanic Cloud. We used the extreme adaptive optics of the SPHERE focal instrument implemented on the ESO Very Large Telescope and operated in its IRDIS imaging mode for the second time with longer exposure time in the H and K filters. Our aim was to (i) increase the number of resolved sources in the core of R136, and (ii) to compare with the first epoch to classify the properties of the detected common sources between the two epochs. Within the field of view (FOV) of 10.8″ × 12.1″ ($2.7\,\text {pc}\times 3.0\, \text {pc}$), we detected 1499 sources in both H and K filters, for which 76 per cent of these sources have visual companions closer than 0.2″. The larger number of detected sources enabled us to better sample the mass function (MF). The MF slopes are estimated at ages of 1, 1.5, and 2 Myr, at different radii, and for different mass ranges. The MF slopes for the mass range of 10–300 M⊙ are about 0.3 dex steeper than the mass range of 3–300 M⊙, for the whole FOV and different radii. Comparing the JHK colours of 790 sources common in between the two epochs, 67 per cent of detected sources in the outer region (r > 3″) are not consistent with evolutionary models at 1–2 Myr and with extinctions similar to the average cluster value, suggesting an origin from ongoing star formation within 30 Doradus, unrelated to R136.

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Chandra Study of the Cepheus B Star‐forming Region: Stellar Populations and the Initial Mass Function

The Astrophysical Journal Supplement Series ◽

10.1086/501453 ◽

2006 ◽

Vol 163 (2) ◽

pp. 306-334 ◽

Cited By ~ 65

Author(s):

Konstantin V. Getman ◽

Eric D. Feigelson ◽

Leisa Townsley ◽

Patrick Broos ◽

Gordon Garmire ◽

...

Keyword(s):

Stellar Populations ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Star Forming

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The influence of a top-heavy integrated galactic IMF and dust on the chemical evolution of high-redshift starbursts

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa848 ◽

2020 ◽

Vol 494 (2) ◽

pp. 2355-2373 ◽

Cited By ~ 2

Author(s):

M Palla ◽

F Calura ◽

F Matteucci ◽

X L Fan ◽

F Vincenzo ◽

...

Keyword(s):

Star Formation ◽

Chemical Evolution ◽

Chemical Elements ◽

High Redshift ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Strong Impact ◽

Star Forming ◽

Abundance Patterns

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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Integrated Near‐Infrared Colors of Star Clusters: Analysis of the Stochastic Effects on the Initial Mass Function

The Astrophysical Journal ◽

10.1086/303921 ◽

1997 ◽

Vol 479 (2) ◽

pp. 764-775 ◽

Cited By ~ 49

Author(s):

Joao F. C. Santos, Jr. ◽

Jay A. Frogel

Keyword(s):

Near Infrared ◽

Star Clusters ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Stochastic Effects

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System initial mass function of the 25 Ori group from planetary-mass objects to intermediate/high-mass stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz756 ◽

2019 ◽

Vol 486 (2) ◽

pp. 1718-1740 ◽

Cited By ~ 4

Author(s):

Genaro Suárez ◽

Juan José Downes ◽

Carlos Román-Zúñiga ◽

Miguel Cerviño ◽

César Briceño ◽

...

Keyword(s):

Power Law ◽

Near Infrared ◽

Mass Range ◽

Mass Function ◽

Initial Mass Function ◽

High Mass ◽

Initial Mass ◽

Formation Mechanisms ◽

Stellar Association ◽

Planetary Mass

Abstract The stellar initial mass function (IMF) is an essential input for many astrophysical studies but only in a few cases has it been determined over the whole cluster mass range, limiting the conclusions about its nature. The 25 Orionis group (25 Ori) is an excellent laboratory for investigating the IMF across the entire mass range of the population, from planetary-mass objects to intermediate/high-mass stars. We combine new deep optical photometry with optical and near-infrared data from the literature to select 1687 member candidates covering a 1.1° radius area in 25 Ori. With this sample we derived the 25 Ori system IMF from 0.012 to 13.1 M⊙. This system IMF is well described by a two-segment power law with Γ = −0.74 ± 0.04 for m < 0.4 M⊙ and Γ = 1.50 ± 0.11 for m ≥ 0.4 M⊙. It is also well described over the whole mass range by a tapered power-law function with Γ = 1.10 ± 0.09, mp = 0.31 ± 0.03 and β = 2.11 ± 0.09. The best lognormal representation of the system IMF has mc = 0.31 ± 0.04 and σ = 0.46 ± 0.05 for m < 1 M⊙. This system IMF does not present significant variations with the radii. We compared the resultant system IMF as well as the brown dwarf/star ratio of 0.16 ± 0.03 that we estimated for 25 Ori with that of other stellar regions with diverse conditions and found no significant discrepancies. These results support the idea that general star-formation mechanisms are probably not strongly dependent on environmental conditions. We found that the substellar and stellar objects in 25 Ori do not have any preferential spatial distributions and confirmed that 25 Ori is a gravitationally unbound stellar association.

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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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