scholarly journals Spectral Evolution Models for the Next Decade

2009 ◽  
Vol 5 (S262) ◽  
pp. 73-80
Author(s):  
Claus Leitherer
Keyword(s):  
Massive Stars ◽  
Spectral Synthesis ◽  
High Redshift ◽  
Mass Function ◽  
Stellar Atmosphere ◽  
Initial Mass Function ◽  
Stellar Content ◽  
Spectral Evolution ◽  
Star Forming ◽  
Main Challenge

AbstractSpectral evolution models are a widely used tool for determining the stellar content of galaxies. I provide a review of the latest developments in stellar atmosphere and evolution models, with an emphasis on massive stars. In contrast to the situation for low- and intermediate-mass stars, the current main challenge for spectral synthesis models are the uncertainties and rapid revision of current stellar evolution models. Spectral libraries, in particular those drawn from theoretical model atmospheres for hot stars, are relatively mature and can complement empirical templates for larger parameter space coverage. I introduce a new ultraviolet spectral library based on theoretical radiation-hydrodynamic atmospheres for hot massive stars. Application of this library to star-forming galaxies at high redshift, i.e., Lyman-break galaxies, will provide new insights into the abundances, initial mass function and ages of stars in the very early universe.

scholarly journals Massive Stars at High Redshifts

2007 ◽  
Vol 3 (S250) ◽  
pp. 415-428
Author(s):  
Max Pettini
Keyword(s):  
Massive Stars ◽  
High Redshift ◽  
Mass Function ◽  
Initial Mass Function ◽  
Stellar Spectra ◽  
Star Forming ◽  
Star Forming Regions ◽  
Look Ahead ◽  
Low Metallicity ◽  
High Redshift Universe

AbstractThe five years that have passed since the last IAU Symposium devoted to massive stars have seen a veritable explosion of data on the high redshift universe. The tools developed to study massive stars in nearby galaxies are finding increasing application to the analysis of the spectra of star-forming regions at redshifts as high as z = 7. In this brief review, I consider three topics of relevance to this symposium: the determination of the metallicities of galaxies at high redshifts from consideration of their ultraviolet stellar spectra; constraints on the initial mass function of massive stars in galaxies at z = 2 − 3; and new clues to the nucleosynthesis of carbon and nitrogen in massive stars of low metallicity. The review concludes with a look ahead at some of the questions that may occupy us for the next five years (at least!).

scholarly journals Populations of OB-type stars in galaxies

2010 ◽  
Vol 6 (S272) ◽  
pp. 233-241
Author(s):  
Christopher J. Evans
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Spectral Synthesis ◽  
High Redshift ◽  
Young Star ◽  
Magellanic Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
External Galaxies

AbstractOne of the challenges for stellar astrophysics is to reach the point at which we can undertake reliable spectral synthesis of unresolved populations in young, star-forming galaxies at high redshift. Here I summarise recent studies of massive stars in the Galaxy and Magellanic Clouds, which span a range of metallicities commensurate with those in high-redshift systems, thus providing an excellent laboratory in which to study the role of environment on stellar evolution. I also give an overview of observations of luminous supergiants in external galaxies out to a remarkable 6.7 Mpc, in which we can exploit our understanding of stellar evolution to study the chemistry and dynamics of the host systems.

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 < 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 Stellar populations in the highest redshift galaxies

2015 ◽  
Vol 11 (A29B) ◽  
pp. 197-198
Author(s):  
Andrew J. Bunker
Keyword(s):  
Galaxy Evolution ◽  
High Redshift ◽  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Forming ◽  
Near Ir ◽  
James Webb Space Telescope ◽  
Large Telescopes ◽  
The Universe

AbstractI discuss stellar populations in galaxies at high redshift (z > 6), in particular the blue rest-frame UV colours which have been detected in recent years through near-IR imaging with HST. These spectral slopes of β < −2 are much more blue than star-forming galaxies at lower redshift, and may suggest less dust obscuration, lower metallicity or perhaps a different initial mass function. I describe current work on the luminosity function of high redshift star- forming galaxies, the evolution of the fraction of strong Lyman-α emitters in this population, and the contribution of the ionizing photon budget from such galaxies towards the reionization of the Universe. I also describe constraints placed by Spitzer/IRAC on stellar populations in galaxies within the first billion years, and look towards future developments in spectroscopy with Extremely Large Telescopes and the James Webb Space Telescope, including the JWST/NIRSpec GTO programme on galaxy evolution at high redshift.

The impact of star formation sampling effects on the spectra of lensed z > 6 galaxies detectable with JWST

2019 ◽  
Vol 492 (2) ◽  
pp. 1706-1712
Author(s):  
Anton Vikaeus ◽  
Erik Zackrisson ◽  
Christian Binggeli
Keyword(s):  
Star Formation ◽  
Spectral Synthesis ◽  
High Redshift ◽  
Formation Rate ◽  
Mass Function ◽  
Spectroscopic Studies ◽  
Initial Mass Function ◽  
James Webb Space Telescope ◽  
Population Iii Stars ◽  
The Impact

ABSTRACT The upcoming James Webb Space Telescope (JWST) will allow observations of high-redshift galaxies at fainter detection levels than ever before, and JWST surveys targeting gravitationally lensed fields are expected to bring z ≳ 6 objects with very low star formation rate (SFR) within reach of spectroscopic studies. As galaxies at lower and lower star formation activity are brought into view, many of the standard methods used in the analysis of integrated galaxy spectra are at some point bound to break down, due to violation of the assumptions of a well-sampled stellar initial mass function (IMF) and a slowly varying SFR. We argue that galaxies with SFR ∼ 0.1 M⊙ yr−1 are likely to turn up at the spectroscopic detection limit of JWST in lensed fields, and investigate to what extent star formation sampling may affect the spectral analysis of such objects. We use the slug spectral synthesis code to demonstrate that such effects are likely to have significant impacts on spectral diagnostics of, for example, the Balmer emission lines. These effects are found to stem primarily from SFRs varying rapidly on short (∼Myr) time-scales due to star formation in finite units (star clusters), whereas the effects of an undersampled IMF is deemed insignificant in comparison. In contrast, the ratio between the He ii- and H i-ionizing flux is found to be sensitive to IMF-sampling as well as ICMF-sampling (sampling of the initial cluster mass function), which may affect interpretations of galaxies containing Population III stars or other sources of hard ionizing radiation.

scholarly journals The star formation process in the Magellanic Clouds

2008 ◽  
Vol 4 (S256) ◽  
pp. 191-202
Author(s):  
J. M. Oliveira
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Critical Density ◽  
Mass Function ◽  
Magellanic Clouds ◽  
Initial Mass Function ◽  
Star Forming ◽  
Bridge Span ◽  
Individual Star ◽  
Low Metallicity

AbstractThe Magellanic Clouds offer unique opportunities to study star formation both on the global scales of an interacting system of gas-rich galaxies, as well as on the scales of individual star-forming clouds. The interstellar media of the Small and Large Magellanic Clouds and their connecting bridge, span a range in (low) metallicities and gas density. This allows us to study star formation near the critical density and gain an understanding of how tidal dwarfs might form; the low metallicity of the SMC in particular is typical of galaxies during the early phases of their assembly, and studies of star formation in the SMC provide a stepping stone to understand star formation at high redshift where these processes can not be directly observed. In this review, I introduce the different environments encountered in the Magellanic System and compare these with the Schmidt-Kennicutt law and the predicted efficiencies of various chemo-physical processes. I then concentrate on three aspects that are of particular importance: the chemistry of the embedded stages of star formation, the Initial Mass Function, and feedback effects from massive stars and its ability to trigger further star formation.

scholarly journals The highly variable time evolution of star-forming cores identified with dendrograms

2020 ◽  
Vol 497 (4) ◽  
pp. 4517-4534
Author(s):  
Rachel A Smullen ◽  
Kaitlin M Kratter ◽  
Stella S R Offner ◽  
Aaron T Lee ◽  
Hope How-Huan Chen
Keyword(s):  
Time Evolution ◽  
Mass Function ◽  
Density Field ◽  
Initial Mass Function ◽  
Stellar Content ◽  
Core Mass ◽  
Structure Variation ◽  
Star Forming ◽  
The Core ◽  
Dense Cores

ABSTRACT We investigate the time evolution of dense cores identified in molecular cloud simulations using dendrograms, which are a common tool to identify hierarchical structure in simulations and observations of star formation. We develop an algorithm to link dendrogram structures through time using the three-dimensional density field from magnetohydrodynamical simulations, thus creating histories for all dense cores in the domain. We find that the population-wide distributions of core properties are relatively invariant in time, and quantities like the core mass function match with observations. Despite this consistency, an individual core may undergo large (&gt;40 per cent), stochastic variations due to the redefinition of the dendrogram structure between time-steps. This variation occurs independent of environment and stellar content. We identify a population of short-lived (&lt;200 kyr) overdensities masquerading as dense cores that may comprise $\sim\!20$ per cent of any time snapshot. Finally, we note the importance of considering the full history of cores when interpreting the origin of the initial mass function; we find that, especially for systems containing multiple stars, the core mass defined by a dendrogram leaf in a snapshot is typically less than the final system stellar mass. This work reinforces that there is no time-stable density contour that defines a star-forming core. The dendrogram itself can induce significant structure variation between time-steps due to small changes in the density field. Thus, one must use caution when comparing dendrograms of regions with different ages or environment properties because differences in dendrogram structure may not come solely from the physical evolution of dense cores.

scholarly journals The Young and the Massive: Stars at the upper end of the Initial Mass Function

2016 ◽  
Vol 12 (S329) ◽  
pp. 104-109
Author(s):  
Saida M. Caballero-Nieves ◽  
P. A. Crowther
Keyword(s):  
Massive Stars ◽  
High Redshift ◽  
Mass Function ◽  
Large Magellanic Cloud ◽  
Initial Mass Function ◽  
Local Universe ◽  
Theoretical Predictions ◽  
Formation And Evolution ◽  
High Redshift Universe ◽  
Open Question

AbstractThe upper mass limit of stars remains an open question in astrophysics. Here we discuss observations of the most massive stars (greater than 100 solar masses) in the local universe and how the observations fit in with theoretical predictions. In particular, the Large Magellanic Cloud plays host to numerous very massive stars, making it an ideal template to study the roles that environment, metallicity, and multiplicity play in the formation and evolution of the most massive stars. We will discuss the work that is instrumental in laying the groundwork for interpreting future observations by James Webb of starburst regions in the high redshift universe.

scholarly journals Ultraviolet photo-ionisation in far-infrared selected sources

2019 ◽  
Vol 627 ◽  
pp. A93 ◽  
Author(s):  
S. J. Curran ◽  
S. W. Duchesne
Keyword(s):  
Massive Stars ◽  
Neutral Hydrogen ◽  
Far Infrared ◽  
Theoretical Models ◽  
Mass Function ◽  
Critical Value ◽  
Initial Mass Function ◽  
X Ray ◽  
Star Forming ◽  
Rule Out

It has been reported that there is a deficit of stellar heated dust, as evident from the lack of far-infrared (FIR) emission, in sources within the Herschel-SPIRE sample with X-ray luminosities exceeding a critical value of LX ∼ 1037 W. Such a scenario would be consistent with the suppression of star formation by the AGN, required by current theoretical models. Since absorption of the 21 cm transition of neutral hydrogen (H I), which traces the star-forming reservoir, also exhibits a critical value in the ultraviolet band (above ionising photon rates of Q ≈ 3 × 1056 s−1), we test the SPIRE sample for the incidence of the detection of 250 μm emission with Q. The highest value at which FIR emission is detected above the SPIRE confusion limit is Q = 8.9 × 1057 s−1, which is ≈30 times that for the H I, with no critical value apparent. Since complete ionisation of the neutral atomic gas is expected at Q ≳ 3 × 1056 s−1, this may suggest that much of the FIR must arise from heating of the dust by the AGN. However, integrating the ionising photon rate of each star over the initial mass function, we cannot rule out that the high observed ionising photon rates are due to a population of hot, massive stars.

scholarly journals An excess of massive stars in the local 30 Doradus starburst

Science ◽  
2018 ◽  
Vol 359 (6371) ◽  
pp. 69-71 ◽  
Author(s):  
F. R. N. Schneider ◽  
H. Sana ◽  
C. J. Evans ◽  
J. M. Bestenlehner ◽  
N. Castro ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Stars ◽  
Formation Rate ◽  
Mass Range ◽  
Mass Function ◽  
Large Magellanic Cloud ◽  
Initial Mass Function ◽  
Star Forming ◽  
30 Doradus ◽  
The Imf

The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large star-formation events in the distant universe. We determined the recent formation history and the initial mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic observations of 247 stars more massive than 15 solar masses (M☉). The main episode of massive star formation began about 8 million years (My) ago, and the star-formation rate seems to have declined in the last 1 My. The IMF is densely sampled up to 200 M☉ and contains 32 ± 12% more stars above 30 M☉ than predicted by a standard Salpeter IMF. In the mass range of 15 to 200 M☉, the IMF power-law exponent is 1.90−0.26+0.37, shallower than the Salpeter value of 2.35.

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