Numerical simulations of the initial mass function and star-formation history using a grid of evolutionary models for star clusters

Abstract I use a sample of more than 120 000 stars in the solar neighbourhood, with parallaxes, magnitudes and colours estimated with unprecedented accuracy by the second data release of the Gaia mission, to derive the initial mass function of the Galactic disc. A full-forward technique is used to take into account, for the population of unresolved binaries, the metallicity distribution and the star formation history, including their variation across the Galactic disc, as well as all the observational effects. The shape of the initial mass function is well represented by a segmented power law with two breaks at characteristic masses. It has a maximum at M ∼ 0.15 M⊙ with significant flattening (possibly a depletion) at lower masses and a slope of α = −1.34 ± 0.07 in the range 0.25 < M/M⊙ < 1. Above 1 M⊙, the initial mass function shows an abrupt decline with a slope ranging from α = −2.68 ± 0.09 to α = −2.41 ± 0.11, depending on the adopted resolution of the star formation history.

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The Star Formation History and IMF in the LMC and SMC from Deep HST Imaging

Symposium - International Astronomical Union ◽

10.1017/s0074180900118200 ◽

1999 ◽

Vol 190 ◽

pp. 351-353

Author(s):

J. Holtzman ◽

J. R. Mould ◽

J. S. Gallagher

Keyword(s):

Star Formation ◽

Mass Function ◽

Initial Mass Function ◽

Solar Neighborhood ◽

Star Formation History ◽

Initial Mass ◽

Luminosity Functions ◽

Formation History

We present deep photometry to V ~ 27.5 obtained with the HST in several fields in the LMC and the SMC. We derive luminosity functions for the faintest stars which are consistent with an initial mass function similar to that of the solar neighborhood, although moderate variations are not excluded. We discuss implications of these observations for the star formation history in these regions of the LMC and SMC.

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Recovering the star formation history of galaxies through spectral fitting: Current challenges

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320001647 ◽

2019 ◽

Vol 15 (S359) ◽

pp. 386-390

Author(s):

Lucimara P. Martins

Keyword(s):

Star Formation ◽

Mass Function ◽

Initial Mass Function ◽

Star Formation History ◽

Stellar Spectra ◽

Spectral Fitting ◽

Formation History ◽

History Of ◽

Nearby Galaxies ◽

Extract Information

AbstractWith the exception of some nearby galaxies, we cannot resolve stars individually. To recover the galaxies star formation history (SFH), the challenge is to extract information from their integrated spectrum. A widely used tool is the full spectral fitting technique. This consists of combining simple stellar populations (SSPs) of different ages and metallicities to match the integrated spectrum. This technique works well for optical spectra, for metallicities near solar and chemical histories not much different from our Galaxy. For everything else there is room for improvement. With telescopes being able to explore further and further away, and beyond the optical, the improvement of this type of tool is crucial. SSPs use as ingredients isochrones, an initial mass function, and a library of stellar spectra. My focus are the stellar libraries, key ingredient for SSPs. Here I talk about the latest developments of stellar libraries, how they influence the SSPs and how to improve them.

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Evidence of spectral evolution on the white dwarf sample from the Gaia mission

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa120 ◽

2020 ◽

Vol 492 (4) ◽

pp. 5003-5010 ◽

Cited By ~ 1

Author(s):

G Ourique ◽

S O Kepler ◽

A D Romero ◽

T S Klippel ◽

D Koester

Keyword(s):

White Dwarf ◽

White Dwarfs ◽

Mass Function ◽

Initial Mass Function ◽

Star Formation History ◽

Initial Mass ◽

Spectral Evolution ◽

Formation History ◽

Magnitude Diagram ◽

Double Population

ABSTRACT Since the Gaia data release 2, several works have been published describing a bifurcation in the observed white dwarf colour−magnitude diagram for ${G_{\mathrm{BP}}}{}-{G_{\mathrm{RP}}}{} \gt 0$. Some possible explanations in the literature include the existence of a double population with different initial mass functions or two distinct populations, one formed by hydrogen-envelope and one formed by helium-envelope white dwarfs. We propose instead spectral evolution to explain the bifurcation. From a population synthesis approach, we find that spectral evolution occurs for effective temperatures below ${\simeq }11\, 000\, \mathrm{K}$ and masses mainly between $0.64\, \mathrm{M}_\odot$ and $0.74\, \mathrm{M}_\odot$, which correspond to around 16 per cent of all DA white dwarfs. We also find that the Gaia white dwarf colour–magnitude diagram indicates a star formation history that decreases abruptly for objects younger than $1.4\, \mathrm{Gyr}$ and a top-heavy initial mass function for the white dwarf progenitors.

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The influence of star clusters on galactic disks: new insights in star-formation in galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308027610 ◽

2008 ◽

Vol 4 (S254) ◽

pp. 209-220

Author(s):

Pavel Kroupa

Keyword(s):

Star Formation ◽

Galaxy Evolution ◽

Stellar Population ◽

Dwarf Galaxy ◽

Star Clusters ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Disk Galaxies ◽

Galactic Disks

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.

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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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