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Star formation

About: Star formation is a research topic. Over the lifetime, 37405 publications have been published within this topic receiving 1808161 citations. The topic is also known as: astrogenesis.


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Journal ArticleDOI
TL;DR: In this article, it is suggested that the mass of the stellar IMF has a universal Salpeter-like form at the upper end, but flattens below a characteristic stellar mass that may vary with time.
Abstract: It has frequently been suggested in the literature that the stellar IMF in galaxies was top-heavy at early times. This would be plausible physically if the IMF depended on a mass-scale such as the Jeans mass that was higher at earlier times because of the generally higher temperatures that were present then. In this paper it is suggested, on the basis of current evidence and theory, that the IMF has a universal Salpeter-like form at the upper end, but flattens below a characteristic stellar mass that may vary with time. Much of the evidence that has been attributed to a top-heavy early IMF, including the ubiquitous G-dwarf problem, the high abundance of heavy elements in clusters of galaxies, and the high rate of formation of massive stars in high-redshift galaxies, can be accounted for with such an IMF if the characteristic stellar mass was several times higher during the early stages of galaxy evolution. However, significant variations in the mass-to-light ratios of galaxies and large amounts of dark matter in stellar remnants are not as easily explained in this way, because they require more extreme and less plausible assumptions about the form and variability of the IMF. Metal-free ‘population III’ stars are predicted to have an IMF that consists exclusively of massive stars, and they could help to account for some of the evidence that has been attributed to a top-heavy early IMF, as well as contributing importantly to the energetics and chemical enrichment of the early Universe.

431 citations

Journal ArticleDOI
TL;DR: Density wave theory of galactic spirals, discussing hydrogen distribution, young star distribution, stellar migration, magnetic field structure, density waves in stellar formation, etc as discussed by the authors, etc.
Abstract: Density wave theory of galactic spirals, discussing hydrogen distribution, young star distribution, stellar migration, magnetic field structure, density waves in stellar formation, etc

431 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present the spatially resolved star formation and chemical enrichment history of the Small Magellanic Cloud (SMC) across the entire central 4° × 45 area of the main body.
Abstract: We present the spatially resolved star formation and chemical enrichment history of the Small Magellanic Cloud (SMC) across the entire central 4° × 45 area of the main body, based on UBVI photometry from our Magellanic Clouds Photometric Survey. We find that (1) approximately 50% of the stars that ever formed in the SMC formed prior to 8.4 Gyr ago (z > 1.2 for WMAP cosmology); (2) the SMC formed relatively few stars between 8.4 and 3 Gyr ago; (3) there was a rise in the mean star formation rate during the most recent 3 Gyr punctuated by "bursts" at ages of 2.5, 0.4, and 0.06 Gyr; (4) the bursts at 2.5 and 0.4 Gyr are temporally coincident with past perigalactic passages of the SMC with the Milky Way; (5) there is preliminary evidence for a large-scale annular structure in the 2.5 Gyr burst; and (6) the chemical enrichment history derived from our analysis is in agreement with the age-metallicity relation of the SMC's star clusters. Consistent interpretation of the data required an ad hoc correction of 0.1–0.2 mag to the B-V colors of 25% of the stars; the cause of this anomaly is unknown, but we show that it does not strongly influence our results.

430 citations

Journal ArticleDOI
TL;DR: In this article, an approximate analytical solution for the evolution of an interstellar neutral cloud exposed to the ionizing radiation of a newly formed star was developed for the formation of a star.
Abstract: An approximate analytical solution is developed for the evolution of an interstellar neutral cloud exposed to the ionizing radiation of a newly formed star. The structure of a steady photoevaporation gas flow off a spherical ionization front is derived even for cases where the ionization front cannot be considered thin, and the downstream flow is not in ionization and thermal equilibrium. Under a wide range of conditions, the ionization front is approximately D-critical, and the ionized gas expands supersonically into the intercloud medium. The ionization front typically drives a strong shock into the initial cloud.

430 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reproduce the blue and red sequences in the observed joint distribution of colour and magnitude for galaxies at low and high redshifts using hybrid N-body/semi-analytic simulations of galaxy formation.
Abstract: We reproduce the blue and red sequences in the observed joint distribution of colour and magnitude for galaxies at low and high redshifts using hybrid N-body/semi-analytic simulations of galaxy formation. The match of model and data is achieved by mimicking the effects of cold flows versus shock heating coupled to feedback from active galactic nuclei (AGNs), as predicted by Dekel and Birnboim. After a critical epoch z ∼ 3, only haloes below a critical shock-heating mass M shock ∼ 10 12 Menjoy gas supply by cold flows and form stars, while cooling and star formation are shut down abruptly above this mass. The shock-heated gas is kept hot because being dilute it is vulnerable to feedback from energetic sources such as AGNs in their self-regulated mode. The shutdown explains in detail the bright-end truncation of the blue sequence at ∼L ∗, the appearance of luminous red-and-dead galaxies on the red sequence starting already at z ∼ 2, the colour bimodality, its strong dependence on environment density and its correlations with morphology and other galaxy properties. Before z ∼ 2-3, even haloes above the shock-heating mass form stars by cold streams penetrating through the hot gas. This explains the bright star forming galaxies at z ∼ 3-4, the early appearance of massive galaxies on the red sequence, the high cosmological star formation rate at high redshifts and the subsequent low rate at low redshifts.

429 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023742
20221,675
20211,238
20201,489
20191,497
20181,530