Cosmic star-formation history

Blobrana

L

Posts: 131433

Date: Jul 31 16:35 2015

RE: Cosmic star-formation history	Permalink

Title: Recycled stellar ejecta as fuel for star formation and implications for the origin of the galaxy mass-metallicity relation Author: Marijke C. Segers, Robert A. Crain, Joop Schaye, Richard G. Bower, Michelle Furlong, Matthieu Schaller, Tom Theuns We use cosmological, hydrodynamical simulations from the EAGLE and OWLS projects to assess the significance of recycled stellar ejecta as fuel for star formation. The fractional contributions of stellar mass loss to the cosmic star formation rate (SFR) and stellar mass densities increase with time, reaching 35% and 19%, respectively, at z=0. The importance of recycling increases steeply with galaxy stellar mass for M_*< 10^10.5 solar masses, and decreases mildly at higher mass. This trend arises from the mass dependence of feedback associated with star formation and AGN, which preferentially suppresses star formation fuelled by recycling. Recycling is more important for satellites than centrals and its contribution decreases with galactocentric radius. The relative contribution of AGB stars increases with time and towards galaxy centers. This is a consequence of the more gradual release of AGB ejecta compared to that of massive stars, and the preferential removal of the latter by outflows and by lock up in stellar remnants. Recycling-fuelled star formation exhibits a tight, positive correlation with galaxy metallicity, with a secondary dependence on the relative abundance of alpha elements (which are predominantly synthesized in massive stars), that is insensitive to the subgrid models for feedback. Hence, our conclusions are directly relevant for the origin of the mass-metallicity relation and metallicity gradients. Applying the relation between recycling and metallicity to the observed mass-metallicity relation yields our best estimate of the mass-dependent contribution of recycling. For centrals with a mass similar to that of the Milky Way, we infer the contributions of recycled stellar ejecta to the SFR and stellar mass to be 35% and 20%, respectively. Read more (2482kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Mar 4 20:25 2015

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Why isnt the universe as bright as it should be? A handful of new stars are born each year in the Milky Way, while many more blink on across the universe. But astronomers have observed that galaxies should be churning out millions more stars, based on the amount of interstellar gas available. Read more __________________

Blobrana

L

Posts: 131433

Date: Nov 7 04:55 2012

Star formation rate	Permalink

Universe's star factory shuts down For a long time the universe has been a giant star-making factory, producing countless stars out of floating gas and dust. But now it seems like this gigantic plant is shutting down. By collecting more and more loose material, growing young stars gain mass - like a snowball rolling in the snow - and eventually become big adult stars. Astronomers have now discovered that this doesn't happen very often anymore. In fact, right now there are 30 times less stars being born than when the universe was younger! It looks like the once flourishing star factory is closing down for good. Read more __________________

Blobrana

L

Posts: 131433

Date: Apr 26 05:39 2012

RE: Cosmic star-formation history	Permalink

Title: Star Formation in the Milky Way and Nearby Galaxies Authors: Robert C. Kennicutt Jr., Neal J. Evans II We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star formation rates are discussed, and updated prescriptions for calculating star formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds. Read more (1604kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Jan 10 11:36 2012

Cosmic star formation rate	Permalink

Title: Cosmic star formation rate: a theoretical approach Authors: L. Vincoletto, F. Matteucci, F. Calura, L. Silva, G. Granato The cosmic star formation rate (CSFR), is an important clue to investigate the history of the assembly and evolution of galaxies. Here, we develop a method to study the CSFR from a purely theoretical point of view. Starting from detailed models of chemical evolution, we obtain the histories of star formation of galaxies of different morphological types. These histories are then used to determine the luminosity functions of the same galaxies by means of a spectro-photometric code. We obtain the CSFR under different hypothesis. First, we study the hypothesis of a pure luminosity evolution scenario, in which all galaxies are supposed to form at the same redshift and then evolve only in luminosity. Then we consider scenarios in which the number density or the slope of the LFs are assumed to vary with redshift. After comparison with available data we conclude that a pure luminosity evolution does not provide a good fit to the data, especially at very high redshift, although many uncertainties are still present in the data. On the other hand, a variation in the number density of ellipticals and spirals as a function of redshift can provide a better fit to the observed CSFR. We also explore cases of variable slope of the LFs with redshift and variations of number density and slope at the same time. We cannot find any of those cases which can improve the fit to the data respect to the solely number density variation. Finally, we compute the evolution of the average cosmic metallicity in galaxies with redshift. Read more (326kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Jan 27 20:43 2009

Cosmic star-formation history	Permalink

Title: Cosmic star-formation history from a non-parametric inversion of infrared galaxy counts Authors: Damien Le Borgne (1 and 2), David Elbaz (1), Pierre Ocvirk (3), Christophe Pichon (2) ((1) CEA/Saclay, DSM/IRFU/SAp, Gif-sur-Yvette, France, (2) Institut d'Astrophysique de Paris, UMR7095, UPMC, Paris, France, (3) Astrophysikalisches Institut Potsdam, Potsdam, Germany) This paper aims at providing new conservative constraints to the cosmic star-formation history from the empirical modelling of mid- and far-infrared data. We perform a non-parametric inversion of galaxy counts at 15, 24, 70, 160, and 850 microns simultaneously. It is a "blind" search (no redshift information is required) of all possible evolutions of the infrared luminosity function of galaxies, from which the evolution of the star-formation rate density and its uncertainties are derived. The cosmic infrared background (CIRB) measurements are used a posteriori to tighten the range of solutions. The inversion relies only on two hypotheses: (1) the luminosity function remains smooth both in redshift and luminosity, (2) a set of infrared spectral energy distributions (SEDs) of galaxies must be assumed. The range of star-formation histories that we derive is well constrained and consistent with redshift-based measurements from deep surveys. The redshift decompositions of the counts are also recovered successfully. Therefore, multi-wavelength counts and CIRB (both projected observations) alone seem to contain enough information to recover the cosmic star-formation history with quantifiable errors. A peak of the SFRD at z~2 is preferred, although higher redshifts are not excluded. We also find a good consistency between the observed evolution of the stellar mass density and the prediction from our model. Finally, the inability of the inversion to model perfectly and simultaneously all the multi-wavelength infrared counts (especially at 160 microns where an excess is seen around 20 mJ) implies either (i) the existence of a sub-population of colder galaxies, (ii) a larger dispersion of dust temperatures among local galaxies than expected, (iii) or a redshift evolution of the infrared SEDs of galaxies. Read more (311kb, PDF) Read more __________________

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