Mass Segregation in the Young SMC Cluster NGC 330

We present a new study of the low end of the stellar IMF of NGC 330, the richest young star cluster in the Small Magellanic Cloud (SMC). Using deep broadband images taken with the HST/WFPC2 we have derived the cluster's luminosity function and constructed the initial mass function (IMF) in the mass range 1 − 7M⊙. We have investigated the IMF as a function of the radial distance from the cluster center. We find that, after correction for background contamination, the IMF is fairly homogeneous with a slope slightly steeper than Salpeter's in the central regions of the cluster (< 40″) but becomes increasingly steeper with distance, indicating a preponderance of massive stars in the core of the cluster. NGC 330 is one of the first clusters for which evidence of mass segregation is directly found.

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The Mass Function of Young Star Clusters in our Galaxy and Nearby Galaxies: Is It Universal?

Symposium - International Astronomical Union ◽

10.1017/s0074180900224327 ◽

2002 ◽

Vol 207 ◽

pp. 515-524

Author(s):

Ram Sagar

Keyword(s):

Star Clusters ◽

Dynamical Evolution ◽

Mass Function ◽

Young Star ◽

Initial Mass Function ◽

Galactocentric Distance ◽

Photometric Observations ◽

Nearby Galaxies ◽

Mass Segregation ◽

Young Star Clusters

Mass functions (MFs) derived from photometric observations of young star clusters of our Galaxy, the Magellanic Clouds (MCs), M31 and M33 have been used to investigate the question of universality of the initial mass function and presence of mass segregation in these systems. Observational determination of the MF slope of young star clusters have an inherent uncertainty of at least ∼ 1.0 dex in the Milky Way and of ∼ 0.4 dex in the MCs. There is no obvious dependence of the MF slope on either galactocentric distance or age of the young star clusters or on the spatial concentration of the stars formed or on the galactic characteristics including metallicity. Effects of mass segregation have been observed in a good number of young stellar groups of our Galaxy and MCs. As their ages are much smaller than their dynamical evolution times, star formation processes seem to be responsible for the observed mass segregation in them.

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The Initial Mass Function in Young Star Clusters

Highlights of Astronomy ◽

10.1017/s1539299600006821 ◽

1986 ◽

Vol 7 ◽

pp. 489-499

Author(s):

Hans Zinnecker

Keyword(s):

Star Formation ◽

Recent Work ◽

Star Clusters ◽

Mass Function ◽

Young Star ◽

Initial Mass Function ◽

Initial Mass ◽

Stellar Content ◽

Young Star Clusters ◽

The Imf

AbstractThis review discusses both the earlier and the most recent work on the IMF in young star clusters. It is argued that the study of the stellar content of young star clusters offers the best chance of developing a theory of star formation and of the IMF.

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Luminosity Function of Some Open Clusters

ISRN Astronomy and Astrophysics ◽

10.5402/2011/127030 ◽

2011 ◽

Vol 2011 ◽

pp. 1-9 ◽

Cited By ~ 2

Author(s):

W. H. Elsanhoury ◽

M. A. Hamdy ◽

M. I. Nouh ◽

A. S. Saad ◽

S. M. Saad

Keyword(s):

Luminosity Function ◽

Mass Function ◽

Statistical Investigation ◽

Open Clusters ◽

Initial Mass Function ◽

Initial Mass ◽

Classical Definition ◽

Different Ages ◽

The Imf

We investigated the luminosity function (LF) and initial mass function (IMF) of some open clusters having different ages. To calculate the LF, we followed the classical definition by van Rhijn (1936). Statistical investigation of the dispersion around a range of magnitudes concerning what is called Wielen dip revealed that the dip is unreal. To confirm the unreality of the dip, we computed the IMF for these open clusters, the statistical investigation of the IMF confirmed the results obtained using the LF, that is, there is no dip for these open clusters under study.

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An excess of massive stars in the local 30 Doradus starburst

Science ◽

10.1126/science.aan0106 ◽

2018 ◽

Vol 359 (6371) ◽

pp. 69-71 ◽

Cited By ~ 86

Author(s):

F. R. N. Schneider ◽

H. Sana ◽

C. J. Evans ◽

J. M. Bestenlehner ◽

N. Castro ◽

...

Keyword(s):

Star Formation ◽

Massive Stars ◽

Formation Rate ◽

Mass Range ◽

Mass Function ◽

Large Magellanic Cloud ◽

Initial Mass Function ◽

Star Forming ◽

30 Doradus ◽

The Imf

The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large star-formation events in the distant universe. We determined the recent formation history and the initial mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic observations of 247 stars more massive than 15 solar masses (M☉). The main episode of massive star formation began about 8 million years (My) ago, and the star-formation rate seems to have declined in the last 1 My. The IMF is densely sampled up to 200 M☉ and contains 32 ± 12% more stars above 30 M☉ than predicted by a standard Salpeter IMF. In the mass range of 15 to 200 M☉, the IMF power-law exponent is 1.90−0.26+0.37, shallower than the Salpeter value of 2.35.

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Radial variation of the stellar mass functions in the globular clusters M15 and M30: clues of a non-standard IMF?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2759 ◽

2020 ◽

Vol 499 (2) ◽

pp. 2390-2400

Author(s):

M Cadelano ◽

E Dalessandro ◽

J J Webb ◽

E Vesperini ◽

D Lattanzio ◽

...

Keyword(s):

Globular Clusters ◽

Hubble Space Telescope ◽

Dynamical Evolution ◽

Mass Function ◽

Initial Mass Function ◽

Radial Variation ◽

Wide Field ◽

Data Set ◽

Central Regions ◽

Mass Segregation

ABSTRACT We exploit a combination of high-resolution Hubble Space Telescope and wide-field ESO-VLT observations to study the slope of the global mass function (αG) and its radial variation (α(r)) in the two dense, massive and post core-collapse globular clusters M15 and M30. The available data set samples the clusters’ main sequence down to ∼0.2 M⊙ and the photometric completeness allows the study of the mass function between 0.40 M⊙ and 0.75 M⊙ from the central regions out to their tidal radii. We find that both clusters show a very similar variation in α(r) as a function of clustercentric distance. They both exhibit a very steep variation in α(r) in the central regions, which then attains almost constant values in the outskirts. Such a behaviour can be interpreted as the result of long-term dynamical evolution of the systems driven by mass-segregation and mass-loss processes. We compare these results with a set of direct N-body simulations and find that they are only able to reproduce the observed values of α(r) and αG at dynamical ages (t/trh) significantly larger than those derived from the observed properties of both clusters. We investigate possible physical mechanisms responsible for such a discrepancy and argue that both clusters might be born with a non-standard (flatter/bottom-lighter) initial mass function.

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The Dynamics of 47 Tucanae

Symposium - International Astronomical Union ◽

10.1017/s0074180900147230 ◽

1985 ◽

Vol 113 ◽

pp. 69-72

Author(s):

G. S. Da Costa ◽

K. C. Freeman

Keyword(s):

Dark Matter ◽

Thermal Equilibrium ◽

Rotation Velocity ◽

Major Axis ◽

Mass Range ◽

Position Angle ◽

Mass Function ◽

Initial Mass Function ◽

Cluster Center ◽

Solar Mass

Observations made at Las Campanas Observatory and at the Anglo-Australian Observatory have been used to determine line-of-sight velocities with an average accuracy of 3 kms−1 for 135 member stars in the globular cluster 47 Tucanae. The velocities were derived from cross-correlation techniques applied to 30 A/mm spectra obtained with digital sky-subtracting detectors. The spectra themselves have been used to analyze the cyanogen anomalies on the red giant branch in this cluster (Norris et al., 1984). When combined with the velocities published by the CORAVEL group (Mayor et al., 1983), these observations yield velocities for 212 stars with projected distances from the cluster center ranging from 3 to 68 core radii. After radial binning and analysis these observations yield the following results:(i) The inner parts of the cluster show appreciable differential rotation with a maximum projected rotation velocity of approximately 6 kms−1 in the region 6–18 core radii. However, at larger radii the rotation declines rapidly and is essentially zero for radii greater than 30 core radii. This result is illustrated in Figure 1. To within the errors of the determinations, the position angle of the maximum rotation and that of the major axis of the stellar density distribution coincide.(ii) In contrast to M3 (Gunn and Griffin 1979), “thermal equilibrium” multimass models (c.f. Da Costa and Freeman 1976) can ONLY reproduce the observed velocity dispersion values by including a substantial amount of “dark matter”; i.e. unlike M3, there is “missing mass” in 47 Tuc. In order to retain a fit to the surface brightness profile of the cluster, this “dark mass” (which provides perhaps 30 to 40 percent of the total cluster mass) cannot have a distribution much different from that of the cluster giants if it is in the form of stars and “thermal equilibrium” is maintained. In this case the obvious candidates for the dark matter are the white dwarf remnants of the stars more massive than the current turnoff mass, though many more such remnants are required than the number expected from extrapolating the present mass function. The difference between M3 and 47 Tuc in this case then implies that the 47 Tuc initial mass function had many more massive stars than did that for M3. The work of Freeman (1977), who demonstrated large IMF variations in the 8 − 1.5 solar mass range in young Magellanic Cloud clusters, provides observational support for this interpretation.

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Do ultracompact dwarf galaxies form monolithically or as merged star cluster complexes?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab330 ◽

2021 ◽

Vol 502 (4) ◽

pp. 5185-5199

Author(s):

Hamidreza Mahani ◽

Akram Hasani Zonoozi ◽

Hosein Haghi ◽

Tereza Jeřábková ◽

Pavel Kroupa ◽

...

Keyword(s):

Dwarf Galaxies ◽

Initial Conditions ◽

Mass Function ◽

Star Cluster ◽

Initial Mass Function ◽

Central Mass ◽

Cluster Complexes ◽

V Band ◽

Stellar Masses ◽

The Imf

ABSTRACT Some ultracompact dwarf galaxies (UCDs) have elevated observed dynamical V-band mass-to-light (M/LV) ratios with respect to what is expected from their stellar populations assuming a canonical initial mass function (IMF). Observations have also revealed the presence of a compact dark object in the centres of several UCDs, having a mass of a few to 15 per cent of the present-day stellar mass of the UCD. This central mass concentration has typically been interpreted as a supermassive black hole, but can in principle also be a subcluster of stellar remnants. We explore the following two formation scenarios of UCDs: (i) monolithic collapse and (ii) mergers of star clusters in cluster complexes as are observed in massively starbursting regions. We explore the physical properties of the UCDs at different evolutionary stages assuming different initial stellar masses of the UCDs and the IMF being either universal or changing systematically with metallicity and density according to the integrated Galactic IMF theory. While the observed elevated M/LV ratios of the UCDs cannot be reproduced if the IMF is invariant and universal, the empirically derived IMF that varies systematically with density and metallicity shows agreement with the observations. Incorporating the UCD-mass-dependent retention fraction of dark remnants improves this agreement. In addition, we apply the results of N-body simulations to young UCDs and show that the same initial conditions describing the observed M/LV ratios reproduce the observed relation between the half-mass radii and the present-day masses of the UCDs. The findings thus suggest that the majority of UCDs that have elevated M/LV ratios could have formed monolithically with significant remnant-mass components that are centrally concentrated, while those with small M/LV values may be merged star cluster complexes.

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The IMF-SFH connection in massive early-type galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316007808 ◽

2015 ◽

Vol 11 (S315) ◽

Author(s):

I. Ferreras ◽

C. Weidner ◽

A. Vazdekis ◽

F. La Barbera

Keyword(s):

Age Distribution ◽

Stellar Populations ◽

Mass Function ◽

Initial Mass Function ◽

Population Synthesis ◽

Early Type ◽

Massive Galaxies ◽

Stellar Initial Mass Function ◽

The Many ◽

The Imf

The stellar initial mass function (IMF) is one of the fundamental pillars in studies of stellar populations. It is the mass distribution of stars at birth, and it is traditionally assumed to be universal, adopting generic functions constrained by resolved (i.e. nearby) stellar populations (e.g., Salpeter 1955; Kroupa 2001; Chabrier 2003). However, for the vast majority of cases, stars are not resolved in galaxies. Therefore, the interpretation of the photo-spectroscopic observables is complicated by the many degeneracies present between the properties of the unresolved stellar populations, including IMF, age distribution, and chemical composition. The overall good match of the photometric and spectroscopic observations of galaxies with population synthesis models, adopting standard IMF choices, made this issue a relatively unimportant one for a number of years. However, improved models and observations have opened the door to constraints on the IMF in unresolved stellar populations via gravity-sensitive spectral features. At present, there is significant evidence of a non-universal IMF in early-type galaxies (ETGs), with a trend towards a dwarf-enriched distribution in the most massive systems (see, e.g., van Dokkum & Conroy 2010; Ferreras et al. 2013; La Barbera et al. 2013). Dynamical and strong-lensing constraints of the stellar M/L in similar systems give similar results, with heavier M/L in the most massive ETGs (see, e.g., Cappellari et al. 2012; Posacki et al. 2015). Although the interpretation of the results is still open to discussion (e.g., Smith 2014; La Barbera 2015), one should consider the consequences of such a bottom-heavy IMF in massive galaxies.

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Origin of the prestellar core mass function and link to the IMF – Herschel first results

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311000470 ◽

2010 ◽

Vol 6 (S270) ◽

pp. 255-262 ◽

Cited By ~ 5

Author(s):

Ph. André ◽

A. Men'shchikov ◽

V. Könyves ◽

D. Arzoumanian

Keyword(s):

Gravitational Instability ◽

Mass Function ◽

Initial Mass Function ◽

Mhd Turbulence ◽

Core Mass ◽

Thin Filaments ◽

Close Relationship ◽

Prestellar Cores ◽

First Results ◽

The Imf

AbstractWe briefly review ground-based (sub)millimeter dust continuum observations of the prestellar core mass function (CMF) and its connection to the stellar initial mass function (IMF). We also summarize the first results obtained on this topic from the Herschel Gould Belt survey, one of the largest key projects with the Herschel Space Observatory. Our early findings with Herschel confirm the existence of a close relationship between the CMF and the IMF. Furthermore, they suggest a scenario according to which the formation of prestellar cores occurs in two main steps: 1) complex networks of long, thin filaments form first, probably as a result of interstellar MHD turbulence; 2) the densest filaments then fragment and develop prestellar cores via gravitational instability.

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