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 Simple interpolation functions for the galaxy-wide stellar initial mass function and its effects in early-type galaxies

2019 ◽  
Vol 490 (1) ◽  
pp. 848-867 ◽  
Author(s):  
J Dabringhausen
Keyword(s):  
Formation Rate ◽  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Early Type ◽  
The Galaxy ◽  
Stellar Initial Mass Function ◽  
Stellar Masses ◽  
Interpolation Functions

ABSTRACT The galaxy-wide stellar initial mass function (IGIMF) of a galaxy is thought to depend on its star formation rate (SFR). Using a catalogue of observational properties of early-type galaxies (ETGs) and a relation that correlates the formation time-scales of ETGs with their stellar masses, the dependencies of the IGIMF on the SFR are translated into dependencies on more intuitive parameters like present-day luminosities in different passbands. It is found that up to a luminosity of approximately 109 L⊙ (quite independent of the considered passband), the total masses of the stellar populations of ETGs are slightly lower than expected from the canonical stellar initial mass function (IMF). However, the actual mass of the stellar populations of the most luminous ETGs may be up to two times higher than expected from a simple stellar population model with the canonical IMF. The variation of the IGIMF with the mass of ETGs is presented here also as convenient functions of the luminosity in various passbands.

scholarly journals The influence of a top-heavy integrated galactic IMF and dust on the chemical evolution of high-redshift starbursts

2020 ◽  
Vol 494 (2) ◽  
pp. 2355-2373 ◽  
Author(s):  
M Palla ◽  
F Calura ◽  
F Matteucci ◽  
X L Fan ◽  
F Vincenzo ◽  
...  
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Chemical Elements ◽  
High Redshift ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Strong Impact ◽  
Star Forming ◽  
Abundance Patterns

ABSTRACT We study the effects of the integrated galactic initial mass function (IGIMF) and dust evolution on the abundance patterns of high redshift starburst galaxies. In our chemical models, the rapid collapse of gas clouds triggers an intense and rapid star formation episode, which lasts until the onset of a galactic wind, powered by the thermal energy injected by stellar winds and supernova explosions. Our models follow the evolution of several chemical elements (C, N, α-elements, and Fe) both in the gas and dust phases. We test different values of β, the slope of the embedded cluster mass function for the IGIMF, where lower β values imply a more top-heavy initial mass function (IMF). The computed abundances are compared to high-quality abundance measurements obtained in lensed galaxies and from composite spectra in large samples of star-forming galaxies in the redshift range 2 ≲ z ≲ 3. The adoption of the IGIMF causes a sensible increase of the rate of star formation with respect to a standard Salpeter IMF, with a strong impact on chemical evolution. We find that in order to reproduce the observed abundance patterns in these galaxies, either we need a very top-heavy IGIMF (β &lt; 2) or large amounts of dust. In particular, if dust is important, the IGIMF should have β ≥ 2, which means an IMF slightly more top-heavy than the Salpeter one. The evolution of the dust mass with time for galaxies of different mass and IMF is also computed, highlighting that the dust amount increases with a top-heavier IGIMF.

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.

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 The sub-solar initial mass function in the Large Magellanic Cloud

2008 ◽  
Vol 4 (S256) ◽  
pp. 250-255
Author(s):  
Dimitrios A. Gouliermis
Keyword(s):  
Star Formation ◽  
Hubble Space Telescope ◽  
Mass Function ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Star Forming ◽  
Advanced Camera For Surveys

AbstractThe Magellanic Clouds offer a unique variety of star forming regions seen as bright nebulae of ionized gas, related to bright young stellar associations. Nowadays, observations with the high resolving efficiency of the Hubble Space Telescope allow the detection of the faintest infant stars, and a more complete picture of clustered star formation in our dwarf neighbors has emerged. I present results from our studies of the Magellanic Clouds, with emphasis in the young low-mass pre-main sequence populations. Our data include imaging with the Advanced Camera for Surveys of the association LH 95 in the Large Magellanic Cloud, the deepest observations ever taken with HST of this galaxy. I discuss our findings in terms of the initial mass function, which we constructed with an unprecedented completeness down to the sub-solar regime, as the outcome of star formation in the low-metallicity environment of the LMC.

scholarly journals The Variation of the Initial Mass Function in Clusters

2004 ◽  
Vol 221 ◽  
pp. 237-246
Author(s):  
K. L. Luhman
Keyword(s):  
Star Formation ◽  
Brown Dwarfs ◽  
Mass Function ◽  
Open Clusters ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Star Forming ◽  
Star Forming Regions

I review recent measurements of the initial mass function of stars and brown dwarfs in star-forming regions and open clusters and summarize the implications of these data for theories of star formation.

scholarly journals STOCHASTIC STAR FORMATION AND A (NEARLY) UNIFORM STELLAR INITIAL MASS FUNCTION

2011 ◽  
Vol 741 (2) ◽  
pp. L26 ◽  
Author(s):  
Michele Fumagalli ◽  
Robert L. da Silva ◽  
Mark R. Krumholz
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Stellar Initial Mass Function
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