THE PROPAGATION OF UNCERTAINTIES IN STELLAR POPULATION SYNTHESIS MODELING. I. THE RELEVANCE OF UNCERTAIN ASPECTS OF STELLAR EVOLUTION AND THE INITIAL MASS FUNCTION TO THE DERIVED PHYSICAL PROPERTIES OF GALAXIES

Aims. Observations of both galaxies in the distant Universe and local starbursts are showing increasing evidence for very hard ionizing spectra that stellar population synthesis models struggle to reproduce. Here we explore the effects of the assumed stellar initial mass function (IMF) on the ionizing photon output of young populations at wavelengths below key ionization energy thresholds. Methods. We use a custom set of binary population and spectral synthesis (BPASS) models to explore the effects of IMF assumptions as a function of metallicity, IMF slope, upper mass limit, IMF power law break mass and sampling. Results. We find that while the flux capable of ionizing hydrogen is only weakly dependent on IMF parameters, the photon flux responsible for the He II and O VI lines is far more sensitive to assumptions. In our current models this flux arises primarily from helium and Wolf-Rayet stars which have partially or fully lost their hydrogen envelopes. The timescales for formation and evolution of both Wolf Rayet stars and helium dwarfs, and hence inferred population age, are affected by choice of model IMF. Even the most extreme IMFs cannot reproduce the He II ionizing flux observed in some high redshift galaxies, suggesting a source other than stellar photospheres. Conclusions. We caution that detailed interpretation of features in an individual galaxy spectrum is inevitably going to be subject to uncertainties in the IMF of its contributing starbursts. We remind the community that the IMF is fundamentally a statistical construct, and that stellar population synthesis models are most effective when considering entire galaxy populations rather than individual objects.

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The Vertical Structure of the Galactic Disc

Symposium - International Astronomical Union ◽

10.1017/s0074180900109064 ◽

1995 ◽

Vol 164 ◽

pp. 389-389

Author(s):

M. Haywood ◽

A.C. Robin ◽

O. Bienaymé

Keyword(s):

Stellar Population ◽

Formation Rate ◽

Mass Range ◽

Mass Function ◽

Initial Mass Function ◽

Population Synthesis ◽

Intermediate Mass ◽

Star Count ◽

Stellar Population Synthesis ◽

Disc Formation

We have analyse star-count data in the direction of the Galactic Poles using a model of stellar population synthesis (Robin & Crézé (1986), Bienaymé, Robin & Crézé (1987)). The HR diagram for disc stars in the model is computed for a given star formation rate history and initial mass function (Haywood, 1994). In a paper submitted to A&A (Haywood et al.), we give a detailed investigation of the effects of these two functions on the simulated star-counts, and compare these with observed V, B-V data from V=5 to 22. We have obtained new constraints on the SFR, which we show has remained constant (to within a factor <3) since the disc formation, and on the IMF in the intermediate mass range (1-2 M⊙). Finally, we also obtain new constraint on the increase of vertical velocity dispersion with age. We state that if the disc does not containt any dynamically important dark mass, then this relation saturates at value smaller than 21 km.s−1.

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The stellar population and initial mass function of NGC 1399 with MUSE

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sty1434 ◽

2018 ◽

Vol 479 (2) ◽

pp. 2443-2456 ◽

Cited By ~ 18

Author(s):

Sam P Vaughan ◽

Roger L Davies ◽

Simon Zieleniewski ◽

Ryan C W Houghton

Keyword(s):

Stellar Population ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass

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Hα and FUV luminosities from a stochastically formed stellar population

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312008721 ◽

2011 ◽

Vol 7 (S284) ◽

pp. 53-55

Author(s):

Nidia Lugo Lopez L. ◽

Gladis Magris C. ◽

Antonio Parravano

Keyword(s):

Power Law ◽

Surface Brightness ◽

Stellar Population ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Low Surface Brightness ◽

Low Surface Brightness Galaxies

AbstractIt has been observed that the ratio of Hα to FUV luminosity (LHα/LFUV) is lower in low surface brightness galaxies. This behaviour has been attributed to systematic variations of the upper mass end and/or the slope of the Initial Mass Function (IMF) Meurer et al. (2009) and Lee et al. (2009)). However these hypotheses do not explain the observed scatter in luminosity ratio (LHα/LFUV). We present a model for the total LHα and LFUV luminosity arising from a randomly populated IMF following the Salpeter power law and the clustering law of Oey & Clarke (2007).

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New indications on the Galactic bulge IMF by microlensing surveys

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308018152 ◽

2007 ◽

Vol 3 (S245) ◽

pp. 367-368

Author(s):

L. Mancini ◽

S. Calchi Novati

Keyword(s):

Mass Spectrum ◽

Stellar Population ◽

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Galactic Bulge

AbstractBasing on recent microlensing observations, we analyse the mass spectrum of the Galactic bulge stellar population and study the slope of the initial mass function.

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Population Synthesis: Challenges for the Next Decade

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310002528 ◽

2009 ◽

Vol 5 (S262) ◽

pp. 55-64

Author(s):

Gustavo Bruzual A.

Keyword(s):

Stellar Evolution ◽

Stellar Population ◽

Stellar Model ◽

Data Sets ◽

Population Synthesis ◽

Current Interest ◽

Recent Advances ◽

Stellar Population Synthesis ◽

Spectral Libraries

AbstractIn this paper I present a brief summary of recent advances in the fields of stellar evolution, stellar model atmospheres, and stellar spectral libraries, which allow us to build more realistic stellar population synthesis models than those available up to now. Applications of these models to problems of current interest are discussed. Problems that need to be understood and data sets that need to be collected in order to solve issues present in these models are listed.

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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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