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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 was shown that in order to reach the accretion rates needed to sustain the observed star formation, additional infall of large amounts of gas from the intergalactic medium (IGM) seems to be required.
Abstract: Evidence for the accretion of cold gas in galaxies has been rapidly accumulating in the past years. HI observations of galaxies and their environment have brought to light new facts and phenomena which are evidence of ongoing or recent accretion: 1) A large number of galaxies are accompanied by gas-rich dwarfs or are surrounded by HI cloud complexes, tails and filaments. It may be regarded as direct evidence of cold gas accretion in the local universe. It is probably the same kind of phenomenon of material infall as the stellar streams observed in the halos of our galaxy and M31. 2) Considerable amounts of extra-planar HI have been found in nearby spiral galaxies. While a large fraction of this gas is produced by galactic fountains, it is likely that a part of it is of extragalactic origin. 3) Spirals are known to have extended and warped outer layers of HI. It is not clear how these have formed, and how and for how long the warps can be sustained. Gas infall has been proposed as the origin. 4) The majority of galactic disks are lopsided in their morphology as well as in their kinematics. Also here recent accretion has been advocated as a possible cause. In our view, accretion takes place both through the arrival and merging of gas-rich satellites and through gas infall from the intergalactic medium (IGM). The infall may have observable effects on the disk such as bursts of star formation and lopsidedness. We infer a mean ``visible'' accretion rate of cold gas in galaxies of at least 0.2 Msol/yr. In order to reach the accretion rates needed to sustain the observed star formation (~1 Msol/yr), additional infall of large amounts of gas from the IGM seems to be required.

480 citations

Journal ArticleDOI
TL;DR: In this article, the authors used cosmological simulations to study a characteristic evolution pattern of high-redshift galaxies, which is consistent with the way galaxies populate the SFR-size-mass space, and with gradients and scatter across the main sequence.
Abstract: We use cosmological simulations to study a characteristic evolution pattern of high-redshift galaxies. Early, stream-fed, highly perturbed, gas-rich discs undergo phases of dissipative contraction into compact, star-forming systems (‘blue’ nuggets) at z ∼ 4–2. The peak of gas compaction marks the onset of central gas depletion and inside-out quenching into compact ellipticals (red nuggets) by z ∼ 2. These are sometimes surrounded by gas rings or grow extended dry stellar envelopes. The compaction occurs at a roughly constant specific star formation rate (SFR), and the quenching occurs at a constant stellar surface density within the inner kpc (Σ 1 ). Massive galaxies quench earlier, faster, and at a higher Σ 1 than lower mass galaxies, which compactify and attempt to quench more than once. This evolution pattern is consistent with the way galaxies populate the SFR-size–mass space, and with gradients and scatter across the main sequence. The compaction is triggered by an intense inflow episode, involving (mostly minor) mergers, counter-rotating streams or recycled gas, and is commonly associated with violent disc instability. The contraction is dissipative, with the inflow rate >SFR, and the maximum Σ 1 anticorrelated with the initial spin parameter. The central quenching is triggered by the high SFR and stellar/supernova feedback (maybe also active galactic nucleus feedback) due to the high central gas density, while the central inflow weakens as the disc vanishes. Suppression of fresh gas supply by a hot halo allows the long-term maintenance of quenching once above a threshold halo mass, inducing the quenching downsizing.

479 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used the model of H2 formation, dissociation, and shielding developed in the previous paper in this series to make theoretical predictions for atomic-to-molecular ratios as a function of galactic properties.
Abstract: Gas in galactic disks is collected by gravitational instabilities into giant atomic-molecular complexes, but only the inner, molecular parts of these structures are able to collapse to form stars. Determining what controls the ratio of atomic-to-molecular hydrogen in complexes is, therefore, a significant problem in star formation and galactic evolution. In this paper, we use the model of H2 formation, dissociation, and shielding developed in the previous paper in this series to make theoretical predictions for atomic-to-molecular ratios as a function of galactic properties. We find that the molecular fraction in a galaxy is determined primarily by its column density and secondarily by its metallicity, and is to a good approximation independent of the strength of the interstellar radiation field. We show that the column of atomic hydrogen required to shield a molecular region against dissociation is ~10 M ☉ pc–2 at solar metallicity. We compare our model to data from recent surveys of the Milky Way and of nearby galaxies, and show that the both the primary dependence of molecular fraction on column density and the secondary dependence on metallicity that we predict are in good agreement with observed galaxy properties.

478 citations

Journal ArticleDOI
TL;DR: In this article, a large set of radiation hydrodynamic simulations of primordial star formation in a fully cosmological context is performed, and the authors find correlations between the final stellar mass and the physical properties of the star-forming cloud.
Abstract: We perform a large set of radiation hydrodynamic simulations of primordial star formation in a fully cosmological context. Our statistical sample of 100 First Stars shows that the first generation of stars has a wide mass distribution M popIII = 10 ~ 1000 M ☉. We first run cosmological simulations to generate a set of primordial star-forming gas clouds. We then follow protostar formation in each gas cloud and the subsequent protostellar evolution until the gas mass accretion onto the protostar is halted by stellar radiative feedback. The accretion rates differ significantly among the primordial gas clouds that largely determine the final stellar masses. For low accretion rates, the growth of a protostar is self-regulated by radiative feedback effects, and the final mass is limited to several tens of solar masses. At high accretion rates the protostar's outer envelope continues to expand, and the effective surface temperature remains low; such protostars do not exert strong radiative feedback and can grow in excess of 100 solar masses. The obtained wide mass range suggests that the first stars play a variety of roles in the early universe, by triggering both core-collapse supernovae and pair-instability supernovae as well as by leaving stellar mass black holes. We find certain correlations between the final stellar mass and the physical properties of the star-forming cloud. These correlations can be used to estimate the mass of the first star from the properties of the parent cloud or of the host halo without following the detailed protostellar evolution.

478 citations

Journal ArticleDOI
TL;DR: In this paper, the authors presented the most extensive and complete study of the properties for the largest sample (46 objects) of gamma-ray burst (GRB) host galaxies.
Abstract: We present the most extensive and complete study of the properties for the largest sample (46 objects) of gamma-ray burst (GRB) host galaxies. The redshift interval and the mean redshift of the sample are 0 < z < 6.3 and z = 0.96 (look-back time: 7.2 Gyr), respectively; 89% of the hosts are at z ? 1.6. Optical-near-IR (NIR) photometry and spectroscopy are used to derive stellar masses, star formation rates (SFRs), dust extinctions, and metallicities. The average stellar mass is 109.3 M ?, with a 1? dispersion of 0.8 dex. The average metallicity for a subsample of 17 hosts is about 1/6 solar and the dust extinction in the visual band (for a subsample of 10 hosts) is AV = 0.5. We obtain new relations to derive SFR from [O?II] or UV fluxes, when Balmer emission lines are not available. SFRs, corrected for dust extinction, aperture-slit loss, and stellar Balmer absorption are in the range 0.01-36 M ? yr?1. The median SFR per unit stellar mass (specific SFR) is 0.8 Gyr?1. Equivalently the inverse quantity, the median formation timescale, is 1.3 Gyr. Most GRBs are associated with the death of young massive stars, more common in star-forming galaxies. Therefore, GRBs are an effective tool to detect star-forming galaxies in the universe. Star-forming galaxies at z < 1.6 are a faint and low-mass population, hard to detect by conventional optical-NIR surveys, unless a GRB event occurs. There is no compelling evidence that GRB hosts are peculiar galaxies. More data on the subclass of short GRB are necessary to establish the nature of their hosts.

478 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