J/A+A/666/A113 Stellar integrated galactic initial mass function (Dib, 2022)
The galaxy-wide stellar initial mass function in the presence of
cluster-to-cluster IMF variations.
Dib S.
<Astron. Astrophys. 666, A113 (2022)>
=2022A&A...666A.113D 2022A&A...666A.113D (SIMBAD/NED BibCode)
ADC_Keywords: Models ; Associations, stellar ; Stars, masses
Keywords: stars: luminosity function, mass function -
galaxies: star clusters: general - galaxies: stellar content -
galaxies: spiral - galaxies: dwarf - galaxies: starburst
Abstract:
We calculate the stellar integrated galactic initial mass function
(IGIMF) in the presence of cluster-to-cluster variations of the IMF.
Variations of the IMF for a population of coeval clusters that
populate the initial cluster mass function (ICLMF) are taken into
account in the form of Gaussian distribution functions of the IMF
parameters. For the tapered power-law function used in this work,
these are the slope at the high-mass end, Γ, the slope at the
low-mass end, Γ, and the characteristic mass Mch. The level of
variations is modeled by varying the width of the Gaussian
distributions. The reference values are the standard deviations of the
parameters observed for the population of young clusters in the
present-day Milky Way, which are σΓ=0.6,
σγ=0.25, and σMch=0.27M ☉. We find that
increasing the levels of dispersion for Γ and γ tends to
moderately flatten the IGIMF at the low and high-mass end,
respectively. The characteristic mass of the IGIMF is, however,
strongly impacted by variations in Mch. Increasing the value of
σMch shifts the peak of the IGIMF to lower masses, rendering
the IGIMF more bottom heavy. This can provide a simple explanation for
the bottom-heavy stellar mass function that is inferred for early-type
galaxies since these are likely the result of a merger of disk
galaxies where the physical conditions of the star-forming gas may
vary significantly both in time and space in the merging system. The
effect of IMF variations on the IGIMF is compared to the effects of
other processes and sources of systematic variations such as those due
to variations in the shape of ICLMF, the gas-phase metallicity, and
the galactic star formation rate (SFR) which can potentially affect
the maximum mass of stellar clusters in a galaxy and set the mean
value of the characteristic mass in clusters. For the various
dependencies we have explored, we found that the effect of IMF
variations is a dominant factor that always affects the characteristic
mass of the IGIMF. For the regimes at low metallicity where the IGIMF
resembles a single power law, an increased level of IMF variations
renders the IGIMF steeper and more bottom heavy, especially at low
SFRs. On the other hand, variations in the IMF in the high mass regime
can be easily dominated by variations in the slope of the ICLMF. We
compare our results of the metallicity and SFR-dependent IGIMF to a
sample of Milky Way ultra-faint dwarf (UFD) satellite galaxies that
have available metallicity measurements. The present-day stellar mass
function of these galaxies is a good analog to the IGIMF at the time
their overall population of stars formed. We show that the slope of
the stellar mass function of the UFD galaxies measured for stars in
the mass range [0.4,0.8]M ☉ can only be reproduced when IMF
variations of the same order as those measured in the present-day
Milky Way are included. Our results suggest that the inclusion of IMF
variations in models of galaxy formation and evolution is of vital
importance in order to improve our understanding of star formation and
star formation feedback effects on galactic scales.
Description:
* Models of the galaxy integrated initial mass function (IGIMF)
* Functional form to describe the IMF in clusters: tapered-power law
* Exponent of the initial cluster mass function in all model: beta=2
* Models in the grid implement a star formation rate-maximum cluster
mass relation (SFR-M{cl,max}) but do not include an SFR-Mch
relation (see text for details)
* All models have a metallicity and density dependence (see text for
details)
* The models correspond to those shown in Figures 7 & 8 of the paper
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
igimf.dat 52 16000 Model data
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Byte-by-byte Description of file: igimf.dat
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Bytes Format Units Label Explanations
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1- 4 F4.2 --- a [0/1.5] Parameter that describes the level of
IMF variations among the populations of
stellar clusters (1)
7- 15 F9.4 Msun/yr SFR Galactic star formation rate
(0.0001, 0.0010, 0.0100, 0.1000, 1.0000,
10.0000, 100.0000, or 1000.0000
18- 22 F5.3 Sun Z Metallicity (in units of the solar metallicity)
(0.001, 0.010, 0.100, 1.000 or 2.000)
25- 34 F10.6 Msun Mass Stellar mass
37- 52 F16.6 Msun/yr IGIMF Integrated galactic initial mass function
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Note (1): Values as follows:
0.00 = no IMF variations
0.50 = moderate IMF variations
1.00 = variations similar to those found in the Milky Way
1.50 = strong IMF variations
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Acknowledgements:
Sami Dib, sami.dib(at)gmail.com
(End) Patricia Vannier [CDS] 10-Aug-2022