Star formation at low rates: impact of lacking massive stars on the evolution of dwarf galaxies

2018 ◽  
Vol 14 (S344) ◽  
pp. 186-189
Author(s):  
P. Steyrleithner ◽  
G. Hensler ◽  
S. Recchi ◽  
S. Ploeckinger
Keyword(s):  
Star Formation ◽  
Numerical Simulations ◽  
Galaxy Evolution ◽  
Dwarf Galaxies ◽  
Massive Stars ◽  
Self Regulation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Single Star ◽  
The Imf

AbstractIn recent years dedicated observations have uncovered star formation at extremely low rates in dwarf galaxies, tidal tails, ram-pressure stripped gas clouds, and the outskirts of galactic disks. At the same time, numerical simulations of galaxy evolution have advanced to higher spatial and mass resolutions, but have yet to account for the underfilling of the uppermost mass bins of stellar initial mass function (IMF) at low star-formation rates. In such situations, simulations may simply scale down the IMF, without realizing that this unrealistically results in fractions of massive stars, along with fractions of massive star feedback energy (e.g., radiation and SNII explosions). Not properly accounting for such parameters has consequences for the self-regulation of star formation, the energetics of galaxies, as well as for the evolution of chemical abundances. Here we present numerical simulations of dwarf galaxies with low star-formation rates allowing for two extreme cases of the IMF: a “filled” case with fractional massive stars vs. a truncated IMF, at which the IMF is built bottom-up until the gas reservoir allows the formation of a last single star at an uppermost mass. The aim of the study is to demonstrate the different effects on galaxy evolution with respect to self-regulation, feedback, and chemistry. The case of a stochastic sampled IMF is situated somewhere in between these extremes.

scholarly journals Star formation at low rates - the impact of lacking massive stars on stellar feedback

2016 ◽  
Vol 11 (S321) ◽  
pp. 99-101 ◽  
Author(s):  
Gerhard Hensler ◽  
Patrick Steyrleithner ◽  
Simone Recchi
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Dwarf Galaxies ◽  
Self Regulation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Stellar Cluster ◽  
Stellar Feedback ◽  
Intermediate Mass Stars ◽  
The Impact

AbstractDue to their low masses dwarf galaxies experience low star-formation rates resulting in stellar cluster masses insufficient to fill the initial mass function (IMF) to the uppermost mass. Numerical simulations usually do not account for the completeness of the IMF, but treat a filed IMF by numbers, masses, and stellar feedback by fractions. To ensure that only entire stars are formed, we consider an IMF filled from the lower-mass regime and truncated where at least one entire massive star is formed.By 3D simulations we investigate the effects of two possible IMFs on the evolution of dwarf galaxies: filled vs. truncated IMF. For the truncated IMF the star-formation self-regulation is suppressed, while the energy release by typeII supernovae is larger, both compared to the filled IMF. Moreover, the abundance ratios of particular elements yielded from massive and intermediate-mass stars differ significantly between the two IMF distributions.

scholarly journals An excess of massive stars in the local 30 Doradus starburst

Science ◽  
2018 ◽  
Vol 359 (6371) ◽  
pp. 69-71 ◽  
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.

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

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.

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

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.

scholarly journals Transition of the initial mass function in the metal-poor environments

2021 ◽  
Author(s):  
Sunmyon Chon ◽  
Kazuyuki Omukai ◽  
Raffaella Schneider
Keyword(s):  
Star Formation ◽  
Mass Distribution ◽  
Massive Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Low Mass Stars ◽  
Filamentary Structure ◽  
Low Mass ◽  
Cloud Core

Abstract We study star cluster formation in a low-metallicity environment using three dimensional hydrodynamic simulations. Starting from a turbulent cloud core, we follow the formation and growth of protostellar systems with different metallicities ranging from 10−6 to 0.1 Z⊙. The cooling induced by dust grains promotes fragmentation at small scales and the formation of low-mass stars with M* ∼ 0.01–0.1 M⊙ While the number of low-mass stars increases with metallicity, when Z/Z⊙ ≳ 10−5. the stellar mass distribution is still top-heavy for Z/Z⊙ ≲ 10−2 compared to the Chabrier initial mass function (IMF). In these cases, star formation begins after the turbulent motion decays and a single massive cloud core monolithically collapses to form a central massive stellar system. The circumstellar disk preferentially feeds the mass to the central massive stars, making the mass distribution top-heavy. When Z/Z⊙ = 0.1, collisions of the turbulent flows promote the onset of the star formation and a highly filamentary structure develops owing to efficient fine-structure line cooling. In this case, the mass supply to the massive stars is limited by the local gas reservoir and the mass is shared among the stars, leading to a Chabrier-like IMF. We conclude that cooling at the scales of the turbulent motion promotes the development of the filamentary structure and works as an important factor leading to the present-day IMF.

scholarly journals The Initial Mass Function of Be Stars

2004 ◽  
Vol 215 ◽  
pp. 83-84
Author(s):  
J. Zorec ◽  
R. Levenhagen ◽  
J. Chauville ◽  
Y. Frémat ◽  
D. Ballereau ◽  
...  
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Be Stars ◽  
Fast Rotation ◽  
Formation Conditions ◽  
The Imf

Allowing for systematic differences in the counting of Be Stars due to their overluminosity, changes produced by their fast rotation on spectral types and time spent in the main sequence, a difference between the IMF (Be) and IMF(B) appears, which indicates that the appearance of the Be phenomenon may relay on differences in the initial star formation conditions.

scholarly journals Star Formation in Cooling Flows

1987 ◽  
Vol 127 ◽  
pp. 167-177
Author(s):  
R. W. O'Connell
Keyword(s):  
Star Formation ◽  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Flow Forming ◽  
Cooling Flows ◽  
Cd Galaxies ◽  
Ngc 1275 ◽  
The Imf

Star formation, probably with an abnormal initial mass function, represents the most plausible sink for the large amounts of material being accreted by cD galaxies from cooling flows. There are three prominent cases (NGC 1275, PKS 0745-191, and Abell 1795) where cooling flows have apparently induced unusual stellar populations. Recent studies show that about 50% of other accreting cD's have significant ultraviolet excesses. It therefore appears that detectable accretion populations are frequently associated with cooling flows. The questions of the form of the IMF, the fraction of the flow forming stars, and the lifetime of the flow remain open.

scholarly journals On the Bulk Yields of Nucleosynthesis from Massive Stars

1977 ◽  
Vol 45 ◽  
pp. 161-164
Author(s):  
W. David Arnett
Keyword(s):  
Solar System ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Iron Group ◽  
Helium Stars ◽  
The Absolute ◽  
The Imf

Preliminary estimates are made of the absolute yields of abundant nuclei synthesized in observed stars. The compositions of helium stars of mass 3 ≤ Mα / Mʘ≤ 64 are presented, taken at the instant of instability. These stars of mass Mα are identified with stars of main sequence mass M. The amount of synthesized matter for each mass M ≥ MʘHe is estimated (Table 1). Using a variety of choices for the initial mass function (IMF) the yield per stellar generation is calculated. For standard choices of the IMF the absolute and relative yields of12C,16O,20Ne,24Mg, the Si to Ca group and the iron group agree with solar system values, to the accuracy of the calculations.

scholarly journals The Resolved Stellar Populations of Leo A & GR 8

1995 ◽  
Vol 164 ◽  
pp. 417-417
Author(s):  
Eline Tolstoy
Keyword(s):  
Numerical Simulation ◽  
Star Formation ◽  
Maximum Likelihood ◽  
Stellar Evolution ◽  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Mass Function ◽  
Initial Mass Function ◽  
Magnitude Diagram ◽  
Maximum Likelihood Technique

The complex effects that determine the shape of an observed Colour Magnitude Diagram (CMD) are best disentangled through numerical simulation. We make synthetic CMDs by randomly extracting stars from theoretical stellar evolution tracks using a series of adopted initial conditions, including an Initial Mass Function. Utilizing reliable error estimates on our photometry provided by the program DoPHOT we apply a Maximum Likelihood technique to quantitatively determine which of the numerous different possible models is the most probable match to the data. From these comparisons we obtain a better understanding of how star formation proceeds in the relatively simple environments provided by Dwarf galaxies.

scholarly journals The Initial Mass Function in Young Star Clusters

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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