Progenitor-mass-dependent yields amplify intrinsic scatter in dwarf-galaxy elemental abundance ratios

ABSTRACT We explore the effect of including progenitor mass- and metallicity-dependent yields, supernova rates and energetics on variations in elemental abundance ratios (particularly [α/Fe]) in dwarf galaxies. To understand how the scatter and overall trends in [α/Fe] are affected by including variable metal yields from a discretely sampled initial mass function, we run FIRE simulations of a dwarf galaxy (M⋆(z = 0$) \sim 10^6\rm \, M_{\odot })$ using nucleosynthetic yields from the NuGrid data base that depend on the stellar progenitor mass and metallicity. While NuGrid exhibits lower aggregate α-element production than default FIRE yields, we find that its explicit mass dependence, even when including turbulent metal diffusion, substantially widens the intrinsic scatter in the simulated [Fe/H]-[α/Fe] – a phenomenon visible in some observations of dwarf galaxies.

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A stochastically sampled IMF alters the stellar content of simulated dwarf galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3331 ◽

2019 ◽

Vol 492 (1) ◽

pp. 8-21 ◽

Cited By ~ 7

Author(s):

Elaad Applebaum ◽

Alyson M Brooks ◽

Thomas R Quinn ◽

Charlotte R Christensen

Keyword(s):

Star Formation ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Mass Function ◽

Initial Mass Function ◽

Gas Content ◽

Stellar Content ◽

Full Spectrum ◽

Cosmological Simulations ◽

Order Of Magnitude

ABSTRACT Cosmological simulations are reaching the resolution necessary to study ultra-faint dwarf galaxies. Observations indicate that in small populations, the stellar initial mass function (IMF) is not fully populated; rather, stars are sampled in a way that can be approximated as coming from an underlying probability density function. To ensure the accuracy of cosmological simulations in the ultra-faint regime, we present an improved treatment of the IMF. We implement a self-consistent, stochastically populated IMF in cosmological hydrodynamic simulations. We test our method using high-resolution simulations of a Milky Way halo, run to z = 6, yielding a sample of nearly 100 galaxies. We also use an isolated dwarf galaxy to investigate the resulting systematic differences in galaxy properties. We find that a stochastic IMF in simulations makes feedback burstier, strengthening feedback, and quenching star formation earlier in small dwarf galaxies. For galaxies in haloes with mass ≲ 108.5 M⊙, a stochastic IMF typically leads to lower stellar mass compared to a continuous IMF, sometimes by more than an order of magnitude. We show that existing methods of ensuring discrete supernovae incorrectly determine the mass of the star particle and its associated feedback. This leads to overcooling of surrounding gas, with at least ∼10 per cent higher star formation and ∼30 per cent higher cold gas content. Going forwards, to accurately model dwarf galaxies and compare to observations, it will be necessary to incorporate a stochastically populated IMF that samples the full spectrum of stellar masses.

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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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Red Halos of Galaxies – Reservoirs of Baryonic Dark Matter?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307013798 ◽

2007 ◽

Vol 3 (S244) ◽

pp. 17-25 ◽

Cited By ~ 1

Author(s):

E. Zackrisson ◽

N. Bergvall ◽

C. Flynn ◽

G. Östlin ◽

G. Micheva ◽

...

Keyword(s):

Dark Matter ◽

Stellar Population ◽

Local Group ◽

Dwarf Galaxies ◽

Mass Function ◽

Initial Mass Function ◽

High Mass ◽

Disk Galaxies ◽

Near Ir ◽

Baryonic Dark Matter

AbstractDeep optical/near-IR surface photometry of galaxies outside the Local Group have revealed faint and very red halos around objects as diverse as disk galaxies and starbursting dwarf galaxies. The colours of these structures are too extreme to be reconciled with stellar populations similar to those seen in the stellar halos of the Milky Way or M31, and alternative explanations like dust reddening, high metallicities or nebular emission are also disfavoured. A stellar population obeying an extremely bottom-heavy initial mass function (IMF), is on the other hand consistent with all available data. Because of its high mass-to-light ratio, such a population would effectively behave as baryonic dark matter and could account for some of the baryons still missing in the low-redshift Universe. Here, we give an overview of current red halo detections, alternative explanations for the origin of the red colours and ongoing searches for red halos around types of galaxies for which this phenomenon has not yet been reported. A number of potential tests of the bottom-heavy IMF hypothesis are also discussed.

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318005513 ◽

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.

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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 Fundamental Plane of cluster spheroidal galaxies at z ∼ 1.3: evidence for mass-dependent evolution

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3109 ◽

2019 ◽

Vol 491 (2) ◽

pp. 1777-1794 ◽

Cited By ~ 4

Author(s):

P Saracco ◽

A Gargiulo ◽

F La Barbera ◽

M Annunziatella ◽

D Marchesini

Keyword(s):

Mass Density ◽

High Redshift ◽

Structural Evolution ◽

Stellar Populations ◽

Mass Function ◽

Initial Mass Function ◽

Fundamental Plane ◽

Stellar Velocity ◽

A Minor ◽

Mass Dependent

ABSTRACT We present spectroscopic observations obtained at the Large Binocular Telescope in the field of the cluster XLSSJ0223−0436 at z = 1.22. We confirm 12 spheroids cluster members and determine stellar velocity dispersion for 7 of them. We combine these data with those in the literature for clusters RXJ0848+4453 at z = 1.27 (8 galaxies) and XMMJ2235−2557 at z = 1.39 (7 galaxies) to determine the Fundamental Plane (FP) of cluster spheroids. We find that the FP at z ∼ 1.3 is offset and rotated (∼3σ) with respect to the local FP. The offset corresponds to a mean evolution Δlog(Mdyn/LB) = (−0.5 ± 0.1)z. High-redshift galaxies follow a steeper mass-dependent Mdyn/LB–Mdyn relation than local ones. Assuming Δ log(Mdyn/LB) = Δ log(M*/LB), higher mass galaxies [log(Mdyn/M⊙) ≥ 11.5] have a higher formation redshift (zf ≥ 6.5) than lower mass ones [zf ≤2 for log(Mdyn/M⊙ ≤ 10)], with a median zf ≃ 2.5 for the whole sample. Also, galaxies with higher stellar mass density host stellar populations formed earlier than those in lower density galaxies. At fixed initial mass function, Mdyn/M* varies systematically with mass and mass density. It follows that the evolution of the stellar populations (M*/LB) accounts for the observed evolution of Mdyn/LB for Mdyn > 1011 M⊙ galaxies, while accounts for ∼85 per cent of the evolution at Mdyn < 1011 M⊙. We find no evidence in favour of structural evolution of individual galaxies, while we find evidences that spheroids later added to the population may account for the observed discrepancy between Δlog(Mdyn/LB) and Δ log(M*/LB) at masses <1011 M⊙. Thus, the evolution of the FP of cluster spheroids is consistent with the mass-dependent and mass density-dependent evolution of their stellar populations superimposed to a minor contribution of spheroids joining the population at later times.

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316011261 ◽

2016 ◽

Vol 11 (S321) ◽

pp. 99-101 ◽

Cited By ~ 2

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.

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The Resolved Stellar Populations of Leo A & GR 8

Symposium - International Astronomical Union ◽

10.1017/s0074180900109349 ◽

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.

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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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