FORMATION OF MASSIVE BLACK HOLES IN DENSE STAR CLUSTERS. II. INITIAL MASS FUNCTION AND PRIMORDIAL MASS SEGREGATION

AbstractStars form in embedded star clusters which play a key role in determining the properties of a galaxy's stellar population. A large fraction of newly born massive stars are shot out from dynamically unstable embedded-cluster cores spreading them to large distances before they explode. Embedded clusters blow out their gas once the feedback energy from the new stellar population overcomes its binding energy, leading to cluster expansion and in many cases dissolution into the galaxy. Galactic disks may be thickened by such processes, and some thick disks may be the result of an early epoch of vigorous star-formation. Binary stellar systems are disrupted in clusters leading to a lower fraction of binaries in the field, while long-lived clusters harden degenerate-stellar binaries such that the SNIa rate may increase by orders of magnitude in those galaxies that were able to form long-lived clusters. The stellar initial mass function of the whole galaxy must be computed by adding the IMFs in the individual clusters. The resulting integrated galactic initial mass function (IGIMF) is top-light for SFRs < 10 M⊙/yr, and its slope and, more importantly, its upper stellar mass limit depend on the star-formation rate (SFR), explaining naturally the mass–metallicity relation of galaxies. Based on the IGIMF theory, the re-calibrated Hα-luminosity–SFR relation implies dwarf irregular galaxies to have the same gas-depletion time-scale as major disk galaxies, implying a major change of our concept of dwarf-galaxy evolution. A galaxy transforms about 0.3 per cent of its neutral gas mass every 10 Myr into stars. The IGIMF-theory also naturally leads to the observed radial Hα cutoff in disk galaxies without a radial star-formation cutoff. It emerges that the thorough understanding of the physics and distribution of star clusters may be leading to a major paradigm shift in our understanding of galaxy evolution.

Download Full-text

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

Download Full-text

MOCCA-SURVEY Database I: Dissolution of tidally filling star clusters harboring black hole subsystem

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319006690 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 438-441 ◽

Cited By ~ 1

Author(s):

Mirek Giersz ◽

Abbas Askar ◽

Long Wang ◽

Arkadiusz Hypki ◽

Agostino Leveque ◽

...

Keyword(s):

Black Hole ◽

Star Clusters ◽

Mass Function ◽

Stellar Mass ◽

Star Cluster ◽

Initial Mass Function ◽

Initial Mass ◽

Dissolution Process ◽

Dissolution Mechanism ◽

Dynamical Equilibrium

AbstractWe investigate the dissolution process of star clusters embedded in an external tidal field and harboring a subsystem of stellar-mass black hole. For this purpose we analyzed the MOCCA models of real star clusters contained in the Mocca Survey Database I. We showed that the presence of a stellar-mass black hole subsystem in tidally filling star cluster can lead to abrupt cluster dissolution connected with the loss of cluster dynamical equilibrium. Such cluster dissolution can be regarded as a third type of cluster dissolution mechanism. We additionally argue that such a mechanism should also work for tidally under-filling clusters with a top-heavy initial mass function.

Download Full-text

The uncertain masses of progenitors of core-collapse supernovae and direct-collapse black holes

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa035 ◽

2020 ◽

Vol 494 (1) ◽

pp. L53-L58 ◽

Cited By ~ 8

Author(s):

Eoin J Farrell ◽

Jose H Groh ◽

Georges Meynet ◽

J J Eldridge

Keyword(s):

Black Holes ◽

Probability Distribution ◽

Evolutionary History ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Core Collapse ◽

Core Mass ◽

Individual Determination

ABSTRACT We show that it is not possible to determine the final mass Mfin of a red supergiant (RSG) at the pre-supernova (SN) stage from its luminosity L and effective temperature Teff alone. Using a grid of stellar models, we demonstrate that for a given value of L and Teff, an RSG can have a range of Mfin as wide as 3 to 45 M⊙. While the probability distribution within these limits is not flat, any individual determination of Mfin for an RSG will be degenerate. This makes it difficult to determine its evolutionary history and to map Mfin to an initial mass. Single stars produce a narrower range that is difficult to accurately determine without making strong assumptions about mass-loss, convection, and rotation. Binaries would produce a wider range of RSG Mfin. However, the final Helium core mass $M_{\operatorname{He-core}}$ is well determined by the final luminosity and we find $\log (M_{\operatorname{He-core}}/\mathrm{M}_{\odot }) = 0.659 \log (L/\mathrm{L}_{\odot }) -2.630$. Using this relationship, we derive $M_{\operatorname{He-core}}$ for directly imaged SN progenitors and one failed SN candidate. The value of Mfin for stripped star progenitors of SNe IIb is better constrained by L and Teff due to the dependence of Teff on the envelope mass Menv for Menv ≲ 1 M⊙. Given the initial mass function, our results apply to the majority of progenitors of core-collapse SNe, failed SNe, and direct-collapse black holes.

Download Full-text

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.

Download Full-text

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.

Download Full-text