scholarly journals Chemical Evolution of the Galactic Disk and Bulge

1995 ◽  
Vol 164 ◽  
pp. 133-149
Author(s):  
Rosemary F.G. Wyse
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Milky Way ◽  
Galactic Disk ◽  
Mass Function ◽  
Initial Mass Function ◽  
List Type ◽  
Dark Halo ◽  
Milky Way Galaxy ◽  
The Galaxy

The Milky Way Galaxy offers a unique opportunity for testing theories of galaxy formation and evolution. The study of the spatial distribution, kinematics and chemical abundances of stars in the Milky Way Galaxy allows one to address specific questions pertinent to this meeting such as (i)When was the Galaxy assembled? Is this an ongoing process? What was the merging history of the Milky Way?(ii)When did star formation occur in what is now “The Milky Way Galaxy”? Where did the star formation occur then? What was the stellar Initial Mass Function?(iii)How much dissipation of energy was there before and during the formation of the different stellar components of the Galaxy?(iv)What are the relationships among the different stellar components of the Galaxy?(v)Was angular momentum conserved during formation of the disk(s) of the Galaxy?(vi)What is the shape of the dark halo?(vii)Is there dissipative (disk) dark matter?

scholarly journals The Initial Mass Function of Young Open Clusters in the Galaxy: A Preliminary Result

2015 ◽  
Vol 12 (S316) ◽  
pp. 357-358
Author(s):  
Beomdu Lim ◽  
Hwankyung Sung ◽  
Hyeonoh Hur ◽  
Byeong-Gon Park
Keyword(s):  
Star Formation ◽  
Environmental Conditions ◽  
Mass Function ◽  
Open Clusters ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Formation Processes ◽  
Global Properties ◽  
Wide Range ◽  
The Galaxy

AbstractThe initial mass function (IMF) is an essential tool with which to study star formation processes. We have initiated the photometric survey of young open clusters in the Galaxy, from which the stellar IMFs are obtained in a homogeneous way. A total of 16 famous young open clusters have preferentially been studied up to now. These clusters have a wide range of surface densities (log σ = −1 to 3 [stars pc−2] for stars with mass larger than 5M⊙) and cluster masses (Mcl = 165 to 50, 000M⊙), and also are distributed in five different spiral arms in the Galaxy. It is possible to test the dependence of star formation processes on the global properties of individual clusters or environmental conditions. We present a preliminary result on the variation of the IMF in this paper.

DARK MATTER IN THE GALAXY

1994 ◽  
Vol 03 (supp01) ◽  
pp. 53-61
Author(s):  
ROSEMARY F.G. WYSE
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Galactic Disk ◽  
Brown Dwarfs ◽  
Mass Function ◽  
Initial Mass Function ◽  
Solar Neighborhood ◽  
Vertical Force ◽  
Chemical Abundances ◽  
Stellar Objects

I will first review the evidence that our Milky Way Galaxy contains a substantial amount of dark matter, and what is known about the spatial distribution of this material, from rotation curve decompositions and from analysis of the vertical force law in the solar neighborhood. All data are consistent with no significant unidentified material in the Galactic disk, requiring that the dark matter be in a spatially-extended distribution. Brown dwarfs, or sub-stellar objects, are often discussed as possible dark-matter candidates, especially in view of the implication from nucleosynthesis calculations that dark baryons exist. The somewhat discour-aging status of recent searches for brown dwarfs is reviewed, together with present understanding of the low-mass stellar initial mass function. I discuss a long-term survey of the motions and chemical abundances of Galactic stars which will provide constraints on the Galactic potential well and the history of Galaxy formation.

DARK MATTER IN SPIRAL HALOS AND THE HALO MASS FUNCTION

1994 ◽  
Vol 03 (supp01) ◽  
pp. 87-92
Author(s):  
KEITH M. ASHMAN ◽  
PAOLO SALUCCI ◽  
MASSIMO PERSIC
Keyword(s):  
Dark Matter ◽  
Hierarchical Clustering ◽  
Galaxy Formation ◽  
Luminosity Function ◽  
Mass Function ◽  
Dark Halo ◽  
Constant Mass ◽  
High Luminosity ◽  
The Galaxy ◽  
Galaxy Luminosity Function

Evidence that low-luminosity spirals have a higher dark matter fraction than their high-luminosity counterparts is discussed. The empirical correlation between dark matter fraction and luminosity is used, in conjunction with the galaxy luminosity function of spirals, to derive the dark halo mass function of these galaxies. The mass function is shown to be consistent with hierarchical clustering models of galaxy formation. This contrasts with previous results based on the assumption of a constant mass-to-light ratio for all spirals, which predict too many low-luminosity galaxies.

scholarly journals The star formation timescale of elliptical galaxies

2019 ◽  
Vol 632 ◽  
pp. A110 ◽  
Author(s):  
Zhiqiang Yan ◽  
Tereza Jerabkova ◽  
Pavel Kroupa
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Mass Function ◽  
Elliptical Galaxies ◽  
Initial Mass Function ◽  
Different Types ◽  
The Galaxy ◽  
Stellar Initial Mass Function ◽  
Low Mass ◽  
Natural Solution

The alpha element to iron peak element ratio, for example [Mg/Fe], is a commonly applied indicator of the galaxy star formation timescale (SFT) since the two groups of elements are mainly produced by different types of supernovae that explode over different timescales. However, it is insufficient to consider only [Mg/Fe] when estimating the SFT. The [Mg/Fe] yield of a stellar population depends on its metallicity. Therefore, it is possible for galaxies with different SFTs and at the same time different total metallicity to have the same [Mg/Fe]. This effect has not been properly taken into consideration in previous studies. In this study, we assume the galaxy-wide stellar initial mass function (gwIMF) to be canonical and invariant. We demonstrate that our computation code reproduces the SFT estimations of previous studies, where only the [Mg/Fe] observational constraint is applied. We then demonstrate that once both metallicity and [Mg/Fe] observations are considered, a more severe “downsizing relation” is required. This means that either low-mass ellipticals have longer SFTs (> 4 Gyr for galaxies with mass below 1010 M⊙) or massive ellipticals have shorter SFTs (≈200 Myr for galaxies more massive than 1011 M⊙) than previously thought. This modification increases the difficulty in reconciling such SFTs with other observational constraints. We show that applying different stellar yield modifications does not relieve this formation timescale problem. The quite unrealistically short SFT required by [Mg/Fe] and total metallicity would be prolonged if a variable stellar gwIMF were assumed. Since a systematically varying gwIMF has been suggested by various observations this could present a natural solution to this problem.

scholarly journals Subhalo destruction in the Apostle and Auriga simulations

2019 ◽  
Vol 492 (4) ◽  
pp. 5780-5793 ◽  
Author(s):  
Jack Richings ◽  
Carlos Frenk ◽  
Adrian Jenkins ◽  
Andrew Robertson ◽  
Azadeh Fattahi ◽  
...  
Keyword(s):  
Dark Matter ◽  
Velocity Distribution ◽  
Galaxy Formation ◽  
Milky Way ◽  
State Of The Art ◽  
Systematic Errors ◽  
Mass Function ◽  
New Method ◽  
The Galaxy

ABSTRACT N-body simulations make unambiguous predictions for the abundance of substructures within dark matter haloes. However, the inclusion of baryons in the simulations changes the picture because processes associated with the presence of a large galaxy in the halo can destroy subhaloes and substantially alter the mass function and velocity distribution of subhaloes. We compare the effect of galaxy formation on subhalo populations in two state-of-the-art sets of hydrodynamical Λcold dark matter (ΛCDM) simulations of Milky Way mass haloes, Apostle and Auriga. We introduce a new method for tracking the orbits of subhaloes between simulation snapshots that gives accurate results down to a few kiloparsecs from the centre of the halo. Relative to a dark matter-only simulation, the abundance of subhaloes in Apostle is reduced by 50 per cent near the centre and by 10 per cent within r200. In Auriga, the corresponding numbers are 80 per cent and 40 per cent. The velocity distributions of subhaloes are also affected by the presence of the galaxy, much more so in Auriga than in Apostle. The differences on subhalo properties in the two simulations can be traced back to the mass of the central galaxies, which in Auriga are typically twice as massive as those in Apostle. We show that some of the results from previous studies are inaccurate due to systematic errors in the modelling of subhalo orbits near the centre of haloes.

scholarly journals Impact of metallicity and star formation rate on the time-dependent, galaxy-wide stellar initial mass function

2018 ◽  
Vol 620 ◽  
pp. A39 ◽  
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.

scholarly journals EMP stars with high mass IMF and hierarchical galaxy formation

2009 ◽  
Vol 5 (S265) ◽  
pp. 128-129
Author(s):  
Yutaka Komiya ◽  
Takuma Suda ◽  
Asao Habe ◽  
Masayuki Y. Fujimoto
Keyword(s):  
Chemical Evolution ◽  
Galaxy Formation ◽  
Galactic Halo ◽  
Early Stage ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Halo Stars ◽  
The Galaxy ◽  
Metallicity Distribution

AbstractExtremely metal-poor (EMP) stars in the Galactic halo are stars formed in the very early stage of the chemical evolution of the Galaxy. In previous study, we proposed that typical mass of EMP stars are massive, based on observations of carbon-enhanced EMP stars. In this study, we build a merger tree of the Galaxy semi-analytically and follow the chemical evolution along the merger tree. We also consider the effect of binary and high-mass initial mass function(IMF). Resultant theoretical metallicity distribution function (MDF) and abundance distribution are compared with observed metal-poor halo stars.

scholarly journals The role of interstellar filaments in regulating the star formation efficiency and shaping the initial mass function

2015 ◽  
Vol 11 (S315) ◽  
pp. 81-84
Author(s):  
Vera Könyves ◽  
Philippe André
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Filamentary Structure ◽  
Submillimeter Wavelengths ◽  
The Galaxy ◽  
External Galaxies ◽  
Space Observatories ◽  
Formation Efficiency

AbstractRecent surveys at infrared and submillimeter wavelengths with the Spitzer and Herschel space observatories suggest that star formation in dense molecular gas is governed by essentially the same “laws” in nearby Galactic clouds and distant external galaxies. This raises the possibility of a unified picture for star formation in the Universe from individual-cloud scales to galaxy–wide scales. We summarize the star formation scenario favored by Herschel studies of the nearest molecular clouds of the Galaxy which point to the key role of the quasi-universal filamentary structure pervading the cold interstellar medium.

scholarly journals The sensitivity of stellar feedback to IMF averaging versus IMF sampling in galaxy formation simulations

2021 ◽  
Vol 502 (4) ◽  
pp. 5417-5437
Author(s):  
Matthew C Smith
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
H Ii Regions ◽  
Stellar Feedback ◽  
Stellar Masses ◽  
The Imf

ABSTRACT Galaxy formation simulations frequently use initial mass function (IMF) averaged feedback prescriptions, where star particles are assumed to represent single stellar populations that fully sample the IMF. This approximation breaks down at high mass resolution, where stochastic variations in stellar populations become important. We discuss various schemes to populate star particles with stellar masses explicitly sampled from the IMF. We use Monte Carlo numerical experiments to examine the ability of the schemes to reproduce an input IMF in an unbiased manner while conserving mass. We present our preferred scheme which can easily be added to pre-existing star formation prescriptions. We then carry out a series of high-resolution isolated simulations of dwarf galaxies with supernovae (SNe), photoionization, and photoelectric heating to compare the differences between using IMF averaged feedback and explicitly sampling the IMF. We find that if SNe are the only form of feedback, triggering individual SNe from IMF averaged rates gives identical results to IMF sampling. However, we find that photoionization is more effective at regulating star formation when IMF averaged rates are used, creating more, smaller H ii regions than the rare, bright sources produced by IMF sampling. We note that the increased efficiency of the IMF averaged feedback versus IMF sampling is not necessarily a general trend and may be reversed depending on feedback channel, resolution and other details. However, IMF sampling is always the more physically motivated approach. We conservatively suggest that it should be used for star particles less massive than $\sim 500\, \mathrm{M_\odot }$.

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