scholarly journals Gaia DR2 reveals a star formation burst in the disc 2–3 Gyr ago

2019 ◽  
Vol 624 ◽  
pp. L1 ◽  
Author(s):  
R. Mor ◽  
A. C. Robin ◽  
F. Figueras ◽  
S. Roca-Fàbrega ◽  
X. Luri
Keyword(s):  
Star Formation ◽  
Statistical Significance ◽  
Formation Rate ◽  
External Perturbation ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Thin Disc ◽  
Galaxy Model ◽  
Non Parametric ◽  
The Imf

We use Gaia data release 2 (DR2) magnitudes, colours, and parallaxes for stars with G <  12 to explore a parameter space with 15 dimensions that simultaneously includes the initial mass function (IMF) and a non-parametric star formation history (SFH) for the Galactic disc. This inference is performed by combining the Besançon Galaxy Model fast approximate simulations (BGM FASt) and an approximate Bayesian computation algorithm. We find in Gaia DR2 data an imprint of a star formation burst 2–3 Gyr ago in the Galactic thin disc domain, and a present star formation rate (SFR) of ≈1 M⊙/yr. Our results show a decreasing trend of the SFR from 9–10 Gyr to 6–7 Gyr ago. This is consistent with the cosmological star formation quenching observed at redshifts z <  1.8. This decreasing trend is followed by a SFR enhancement starting at ∼5 Gyr ago and continuing until ∼1 Gyr ago which is detected with high statistical significance by discarding the null hypothesis of an exponential SFH with a p-value = 0.002. We estimate, from our best fit model, that about 50% of the mass used to generate stars, along the thin disc life, was expended in the period from 5 to 1 Gyr ago. The timescale and the amount of stellar mass generated during the SFR enhancement event lead us to hypothesise that its origin, currently under investigation, is not intrinsic to the disc. Thus, an external perturbation is needed for its explanation. Additionally, for the thin disc we find a slope of the IMF of α3 ≈ 2 for masses M >  1.53 M⊙ and α2 ≈ 1.3 for the mass range between 0.5 and 1.53 M⊙. This is the first time that we consider a non-parametric SFH for the thin disc in the Besançon Galaxy Model. This new step, together with the capabilities of the Gaia DR2 parallaxes to break degeneracies between different stellar populations, allow us to better constrain the SFH and the IMF.

scholarly journals The Stellar Populations in Local Group Dwarf Galaxies

1995 ◽  
Vol 164 ◽  
pp. 175-180
Author(s):  
Abhijit Saha
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Formation Rate ◽  
Stellar System ◽  
Mass Function ◽  
Open Clusters ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Physical Parameters ◽  
Stellar Content

The aim of the study of the populations in a stellar system is to understand and be able to describe the stellar content of a system in terms of physical parameters such as the age, star formation history, chemical enrichment history, initial mass function (IMF), environment, and dynamical history of the system. This is done given an understanding of stellar evolution and the ability to express the outcome in “observer parameters”, particularly a color-magnitude diagram (CMD), kinematics, and metallicity. From this perspective, the simplest systems are the galactic clusters and the globular clusters, where all the component stars are coeval and of the same metallicity. The current state of knowledge for these are discussed by others in this conference. We proceed to the next level of complexity (where metallicities are not necessarily all the same, and nor are the stars all coeval), and try to decompose their stellar content, particularly in terms of star formation rate and metallicity. In this regard the two classes of objects that come to mind are the dwarf spheroidals, and the dwarf irregulars. Both these classes of objects are more massive than the open clusters and globular clusters, and show evidence of complexities in their star formation histories, without being so convolved as to make such a study intractable. As we shall see, recent studies along these lines have presented some puzzling problems. Moreover, these are the smallest independent galaxies, and the study of star formation in these is likely to shed light on the history and formation of larger and more complex galaxies.

scholarly journals The IMF and star-formation history of the ionizing cluster of 30 Doradus

1999 ◽  
Vol 193 ◽  
pp. 495-496
Author(s):  
Fernando J. Selman ◽  
Jorge Melnick ◽  
Guillermo L. Bosch ◽  
Roberto J. Terlevich
Keyword(s):  
Star Formation ◽  
Power Law ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Formation History ◽  
Formation History ◽  
History Of ◽  
Single Power ◽  
30 Doradus ◽  
The Imf

A new method is used to determine masses, ages, and reddening for the stars of the starburst cluster NGC 2070 in 30 Doradus. The data are consistent with a star-formation rate which increases exponentially with a characteristic rise time of 1.7 Myr, independent of mass, starting 7 Myr ago. The IMF is consistent with a single power law IMF with Salpeter slope over the whole 3 M⊙ < M < 120 M⊙ range investigated, with evidence for flattening for the innermost radial bin.

scholarly journals Is it possible to reconcile extragalactic IMF variations with a universal Milky Way IMF?

2019 ◽  
Vol 485 (4) ◽  
pp. 4852-4862 ◽  
Author(s):  
Dávid Guszejnov ◽  
Philip F Hopkins ◽  
Andrew S Graus
Keyword(s):  
Star Formation ◽  
Power Law ◽  
Milky Way ◽  
Extreme Environments ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Arbitrary Power ◽  
Power Law Function ◽  
The Imf

Abstract One of the most robust observations of the stellar initial mass function (IMF) is its near-universality in the Milky Way and neighbouring galaxies. But recent observations of early-type galaxies can be interpreted to imply a ‘bottom-heavy’ IMF, while others of ultrafaint dwarfs could imply a ‘top-heavy’ IMF. This would impose powerful constraints on star formation models. We explore what sort of ‘cloud-scale’ IMF models could possibly satisfy these constraints. We utilize simulated galaxies that reproduce (broadly) the observed galaxy properties, while they also provide the detailed star formation history and properties of each progenitor star-forming cloud. We then consider generic models where the characteristic mass of the IMF is some arbitrary power-law function of progenitor cloud properties, along with well-known literature IMF models which scale with Jeans mass, ‘turbulent Bonnor–Ebert mass’, temperature, the opacity limit, metallicity, or the ‘protostellar heating mass’. We show that no IMF models currently in the literature – nor any model where the turnover mass is an arbitrary power-law function of a combination of cloud temperature/density/size/metallicity/velocity dispersion/magnetic field – can reproduce the claimed IMF variation in ellipticals or dwarfs without severely violating observational constraints in the Milky Way. Specifically, they predict too much variation in the ‘extreme’ environments of the Galaxy compared to that observed. Either the IMF varies in a more complicated manner, or alternative interpretations of the extragalactic observations must be explored.

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.

scholarly journals Chemical evolution of ultrafaint dwarf galaxies: testing the IGIMF

2020 ◽  
Vol 495 (3) ◽  
pp. 3276-3294
Author(s):  
E Lacchin ◽  
F Matteucci ◽  
F Vincenzo ◽  
M Palla
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Galactic Halo ◽  
Formation Rate ◽  
Chemical Species ◽  
Chemical Properties ◽  
Building Blocks ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History

ABSTRACT We test the integrated galactic initial mass function (IGIMF) on the chemical evolution of 16 ultrafaint dwarf (UFD) galaxies discussing in detail the results obtained for three of them: Boötes I, Boötes II, and Canes Venatici I, taken as prototypes of the smallest and the largest UFDs. These objects have very small stellar masses (∼103–104 M⊙) and quite low metallicities ([Fe/H] &lt; −1.0 dex). We consider four observational constraints: the present-day stellar mass, the [α/Fe] versus [Fe/H] relation, the stellar metallicity distribution function and the cumulative star formation history. Our model follows in detail the evolution of several chemical species (H, He, α-elements, and Fe). We take into account detailed nucleosynthesis and gas flows (in and out). Our results show that the IGIMF, coupled with the very low star formation rate predicted by the model for these galaxies (∼10−4–10−6 M⊙yr−1), cannot reproduce the main chemical properties, because it implies a negligible number of core-collapse SNe and even Type Ia SNe, the most important polluters of galaxies. On the other hand, a constant classical Salpeter IMF gives the best agreement with data, but we cannot exclude that other formulations of the IGIMF could reproduce the properties of these galaxies. Comparing with Galaxy data, we suggest that UFDs could not be the building blocks of the entire Galactic halo, although more data are necessary to draw firmer conclusions.

scholarly journals Recalibrating the cosmic star formation history

2019 ◽  
Vol 490 (4) ◽  
pp. 5359-5365 ◽  
Author(s):  
Stephen M Wilkins ◽  
Christopher C Lovell ◽  
Elizabeth R Stanway
Keyword(s):  
Star Formation ◽  
Spectral Synthesis ◽  
Mass Density ◽  
Formation Rate ◽  
Thermal Infrared ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Formation History ◽  
Binary Evolution

ABSTRACT The calibrations linking observed luminosities to the star formation rate (SFR) depend on the assumed stellar population synthesis model, initial mass function, star formation and metal enrichment history, and whether reprocessing by dust and gas is included. Consequently the shape and normalization of the inferred cosmic star formation history is sensitive to these assumptions. Using v2.2.1 of the Binary Population and Spectral Synthesis (bpass) model we determine a new set of calibration coefficients for the ultraviolet, thermal infrared, and hydrogen recombination lines. These ultraviolet and thermal infrared coefficients are 0.15–0.2 dex higher than those widely utilized in the literature while the H α coefficient is ∼0.35 dex larger. These differences arise in part due to the inclusion binary evolution pathways but predominantly reflect an extension in the IMF to 300 M⊙ and a change in the choice of reference metallicity. We use these new coefficients to recalibrate the cosmic star formation history, and find improved agreement between the integrated cosmic star formation history and the in situ measured stellar mass density as a function of redshift. However, these coefficients produce new tension between SFR densities inferred from the ultraviolet and thermal infrared and those from H α.

Recovering the star formation history of galaxies through spectral fitting: Current challenges

2019 ◽  
Vol 15 (S359) ◽  
pp. 386-390
Author(s):  
Lucimara P. Martins
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Stellar Spectra ◽  
Spectral Fitting ◽  
Formation History ◽  
History Of ◽  
Nearby Galaxies ◽  
Extract Information

AbstractWith the exception of some nearby galaxies, we cannot resolve stars individually. To recover the galaxies star formation history (SFH), the challenge is to extract information from their integrated spectrum. A widely used tool is the full spectral fitting technique. This consists of combining simple stellar populations (SSPs) of different ages and metallicities to match the integrated spectrum. This technique works well for optical spectra, for metallicities near solar and chemical histories not much different from our Galaxy. For everything else there is room for improvement. With telescopes being able to explore further and further away, and beyond the optical, the improvement of this type of tool is crucial. SSPs use as ingredients isochrones, an initial mass function, and a library of stellar spectra. My focus are the stellar libraries, key ingredient for SSPs. Here I talk about the latest developments of stellar libraries, how they influence the SSPs and how to improve them.

scholarly journals The effects of star formation history in the SFR–M* relation of H ii galaxies

2020 ◽  
Vol 500 (3) ◽  
pp. 3240-3253
Author(s):  
Amanda R Lopes ◽  
Eduardo Telles ◽  
Jorge Melnick
Keyword(s):  
Star Formation ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Star Formation History ◽  
Spectral Energy ◽  
Distribution Fitting ◽  
Good Tool ◽  
Star Forming ◽  
Additional Information ◽  
Star Formation Histories

ABSTRACT We discuss the implications of assuming different star formation histories (SFH) in the relation between star formation rate (SFR) and mass derived by the spectral energy distribution fitting (SED). Our analysis focuses on a sample of H ii galaxies, dwarf starburst galaxies spectroscopically selected through their strong narrow emission lines in SDSS DR13 at z &lt; 0.4, cross-matched with photometric catalogues from GALEX, SDSS, UKIDSS, and WISE. We modelled and fitted the SEDs with the code CIGALE adopting different descriptions of SFH. By adding information from different independent studies, we find that H ii galaxies are best described by episodic SFHs including an old (10 Gyr), an intermediate age (100−1000 Myr) and a recent population with ages &lt; 10 Myr. H ii galaxies agree with the SFR−M* relation from local star-forming galaxies, and only lie above such relation when the current SFR is adopted as opposed to the average over the entire SFH. The SFR−M* demonstrated not to be a good tool to provide additional information about the SFH of H ii galaxies, as different SFH present a similar behaviour with a spread of &lt;0.1 dex.

scholarly journals Quenching by gas compression and consumption

2019 ◽  
Vol 624 ◽  
pp. A81 ◽  
Author(s):  
Allison W. S. Man ◽  
Matthew D. Lehnert ◽  
Joël D. R. Vernet ◽  
Carlos De Breuck ◽  
Theresa Falkendal
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Relative Strength ◽  
Star Formation History ◽  
Molecular Gas ◽  
Host Galaxies ◽  
Massive Galaxies ◽  
Star Forming ◽  
Gas Compression ◽  
Formation History

The objective of this work is to study how active galactic nuclei (AGN) influence star formation in host galaxies. We present a detailed investigation of the star-formation history and conditions of a z = 2.57 massive radio galaxy based on VLT/X-shooter and ALMA observations. The deep rest-frame ultraviolet spectrum contains photospheric absorption lines and wind features indicating the presence of OB-type stars. The most significantly detected photospheric features are used to characterize the recent star formation: neither instantaneous nor continuous star-formation history is consistent with the relative strength of the Si IIλ1485 and S Vλ1502 absorption. Rather, at least two bursts of star formation took place in the recent past, at 6+1-2 Myr and ≳20 Myr ago, respectively. We deduce a molecular H2 gas mass of (3.9 ± 1.0) × 1010 M⊙ based on ALMA observations of the [C I] 3P2−3P1 emission. The molecular gas mass is only 13% of its stellar mass. Combined with its high star-formation rate of (1020-170+190 M⊙ yr-1, this implies a high star-formation efficiency of (26 ± 8) Gyr−1 and a short depletion time of (38 ± 12) Myr. We attribute the efficient star formation to compressive gas motions in order to explain the modest velocity dispersions (⩽55 km s−1) of the photospheric lines and of the star-forming gas traced by [C I]. Because of the likely very young age of the radio source, our findings suggest that vigorous star formation consumes much of the gas and works in concert with the AGN to remove any residual molecular gas, and eventually quenching star formation in massive galaxies.

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