The Global Schmidt law in star forming galaxies
TL;DR: In this paper, the Schmidt law was used to model the global star formation law over the full range of gas densities and star formation rates observed in galaxies, and the results showed that the SFR scales with the ratio of the gas density to the average orbital timescale.
Abstract: Measurements of Hα, H I, and CO distributions in 61 normal spiral galaxies are combined with published far-infrared and CO observations of 36 infrared-selected starburst galaxies, in order to study the form of the global star formation law over the full range of gas densities and star formation rates (SFRs) observed in galaxies. The disk-averaged SFRs and gas densities for the combined sample are well represented by a Schmidt law with index N = 1.4 ± 0.15. The Schmidt law provides a surprisingly tight parametrization of the global star formation law, extending over several orders of magnitude in SFR and gas density. An alternative formulation of the star formation law, in which the SFR is presumed to scale with the ratio of the gas density to the average orbital timescale, also fits the data very well. Both descriptions provide potentially useful "recipes" for modeling the SFR in numerical simulations of galaxy formation and evolution.
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TL;DR: It is shown that baryon-induced features in the initial conditions of the Universe are reflected in distorted form in the low-redshift galaxy distribution, an effect that can be used to constrain the nature of dark energy with future generations of observational surveys of galaxies.
Abstract: The cold dark matter model has become the leading theoretical picture for the formation of structure in the Universe. This model, together with the theory of cosmic inflation, makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability. Testing this model requires that the precise measurements delivered by galaxy surveys can be compared to robust and equally precise theoretical calculations. Here we present a simulation of the growth of dark matter structure using 2,1603 particles, following them from redshift z = 127 to the present in a cube-shaped region 2.230 billion lightyears on a side. In postprocessing, we also follow the formation and evolution of the galaxies and quasars. We show that baryon-induced features in the initial conditions of the Universe are reflected in distorted form in the low-redshift galaxy distribution, an effect that can be used to constrain the nature of dark energy with future generations of observational surveys of galaxies.
4,814 citations
TL;DR: In this paper, the relation between stellar mass and gas-phase metallicity was studied using the Sloan Digital Sky Survey imaging and spectroscopy of ~53,000 star-forming galaxies at z = 0.1.
Abstract: We utilize Sloan Digital Sky Survey imaging and spectroscopy of ~53,000 star-forming galaxies at z ~ 0.1 to study the relation between stellar mass and gas-phase metallicity. We derive gas-phase oxygen abundances and stellar masses using new techniques that make use of the latest stellar evolutionary synthesis and photoionization models. We find a tight (?0.1 dex) correlation between stellar mass and metallicity spanning over 3 orders of magnitude in stellar mass and a factor of 10 in metallicity. The relation is relatively steep from 108.5 to 1010.5 M? h, in good accord with known trends between luminosity and metallicity, but flattens above 1010.5 M?. We use indirect estimates of the gas mass based on the H? luminosity to compare our data to predictions from simple closed box chemical evolution models. We show that metal loss is strongly anticorrelated with baryonic mass, with low-mass dwarf galaxies being 5 times more metal depleted than L* galaxies at z ~ 0.1. Evidence for metal depletion is not confined to dwarf galaxies but is found in galaxies with masses as high as 1010 M?. We interpret this as strong evidence of both the ubiquity of galactic winds and their effectiveness in removing metals from galaxy potential wells.
3,621 citations
TL;DR: The Virgo Consortium's EAGLE project as discussed by the authors is a suite of hydrodynamical simulations that follow the formation of galaxies and black holes in representative volumes, where thermal energy is injected into the gas, allowing winds to develop without predetermined speed or mass loading factors.
Abstract: We introduce the Virgo Consortium's EAGLE project, a suite of hydrodynamical simulations that follow the formation of galaxies and black holes in representative volumes. We discuss the limitations of such simulations in light of their finite resolution and poorly constrained subgrid physics, and how these affect their predictive power. One major improvement is our treatment of feedback from massive stars and AGN in which thermal energy is injected into the gas without the need to turn off cooling or hydrodynamical forces, allowing winds to develop without predetermined speed or mass loading factors. Because the feedback efficiencies cannot be predicted from first principles, we calibrate them to the z~0 galaxy stellar mass function and the amplitude of the galaxy-central black hole mass relation, also taking galaxy sizes into account. The observed galaxy mass function is reproduced to ≲0.2 dex over the full mass range, 108
2,828 citations
Cites methods from "The Global Schmidt law in star form..."
...First, under the assumption that the gas is self-gravitating, we can rewrite the observed Kennicutt-Schmidt star formation law (Kennicutt 1998), Σ̇∗ = A(Σg/1 M pc −2)n, as a pressure law: ṁ∗ = mgA ( 1 M pc −2)−n ( γ G fgP )(n−1)/2 , (1) where mg is the gas particle mass, γ = 5/3 is the ratio of…...
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...We use A = 1.515 × 10−4 M yr−1 kpc−2 and n = 1.4, where we have decreased the amplitude by a factor 1.65 relative to the value used by Kennicutt (1998) because we use a Chabrier rather than a Salpeter stellar initial mass function (IMF)....
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TL;DR: In this paper, the authors review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies.
Abstract: 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.
2,525 citations
Cites background or methods from "The Global Schmidt law in star form..."
...The High-density Regime The two regimes discussed above were able to reproduce all of the early observations of the large-scale star formation law by Kennicutt (1989, 1998b) and Martin & Kennicutt (2001)....
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...Kennicutt (1998b) pointed out that the SFR surface densities also correlate tightly with the ratio of the gas surface density to the local dynamical time, defined in that case to be the average orbit time....
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...…Σ(SFR) and the ratio of gas density to local dynamical time (Σgas/τdyn) shows a correlation that is nearly as tight as the conventional Schmidt law (Kennicutt 1998b), and it also removes the double sequence of disks and starbursts that results if X(CO) is systematically lower in the starbursts…...
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...Other data (including Kennicutt 1998b) are overplotted as described in the figure legend and caption....
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...The immense dispersion in SFR properties seen in Figure 9 collapses to a remarkably tight scaling law when the SFR surface densities (Σ(SFR)) are plotted against mean gas surface densities (Σgas) (Kennicutt 1998b)....
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TL;DR: In this paper, an overall theoretical framework and the observations that motivate it are outlined, outlining the key dynamical processes involved in star formation, including turbulence, magnetic fields, and self-gravity.
Abstract: We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating overdensities to initiate gravitational contraction or collapse, and countering the effects of gravity in these overdense regions. The key dynamical processes involved in star formation—turbulence, magnetic fields, and self-gravity— are highly nonlinear and multidimensional. Physical arguments are used to identify and explain the features and scalings involved in star formation, and results from numerical simulations are used to quantify these effects. We divide star formation into large-scale and small-scale regimes and review each in turn. Large scales range from galaxies to giant molecular clouds (GMCs) and their substructures. Important problems include how GMCs form and evolve, what determines the star formation rate (SFR), and what determines the initial mass function (IMF). Small scales range from dense cores to the protostellar systems they beget. We discuss formation of both low- and high-mass stars, including ongoing accretion. The development of winds and outflows is increasingly well understood, as are the mechanisms governing angular momentum transport in disks. Although outstanding questions remain, the framework is now in place to build a comprehensive theory of star formation that will be tested by the next generation of telescopes.
2,522 citations
Cites background from "The Global Schmidt law in star form..."
...This has been confirmed by Kennicutt (1998); the resulting two forms for the KS law are Σ̇∗ = 0.017ΣgΩ ≃ (2.5±0.7)×10−4 ( Σg 1 M⊙ pc−2 )1.4±0.15 M⊙ yr −1 kpc−2....
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...49g for a sample comprised of both normal and starburst galaxies (Kennicutt, 1998; Downes & Solomon, 1998)....
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...Kennicutt (1998) studied correlations of global averages of Σ̇∗ with Σg (again combining atomic and molecular gas)....
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References
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Book•
01 Jan 1989
TL;DR: In this paper, a comparison of theory with observations internal dynamics of gaseous nebulae interstellar dust H II regions in the galactic context is presented. But the results are limited to the case of active galactic nuclei.
Abstract: Photoionization equilibrium thermal equilibrium calculation of emitted spectrum comparison of theory with observations internal dynamics of gaseous nebulae interstellar dust H II regions in the galactic context planetary nebulae nova and supernova remnants active galactic nuclei - diagnostic and physics active galactic nuclei - results.
6,090 citations
TL;DR: At the highest luminosities (Lir > 1012 ), nearly all objects appear to be advanced mergers powered by a mixture of circumnuclear starburst and active galactic nucleus energy sources, both of which are fueled by an enormous concentration of molecular gas that has been funneled into the merger nucleus as discussed by the authors.
Abstract: ▪ Abstract At luminosities above 1011 , infrared galaxies become the dominant population of extragalactic objects in the local Universe (z ≲ 0.3), being more numerous than optically selected starburst and Seyfert galaxies and quasi-stellar objects at comparable bolometric luminosity. The trigger for the intense infrared emission appears to be the strong interaction/merger of molecular gas-rich spirals, and the bulk of the infrared luminosity for all but the most luminous objects is due to dust heating from an intense starburst within giant molecular clouds. At the highest luminosities (Lir > 1012 ), nearly all objects appear to be advanced mergers powered by a mixture of circumnuclear starburst and active galactic nucleus energy sources, both of which are fueled by an enormous concentration of molecular gas that has been funneled into the merger nucleus. These ultraluminous infrared galaxies may represent an important stage in the formation of quasi-stellar objects and powerful radio galaxies. They may al...
2,911 citations
"The Global Schmidt law in star form..." refers background in this paper
...Since the starbursts are often concentrated in compact circumnuclear disks (e.g., Scoville et al. 1994; Sanders & Mirabel 1996; Smith & Harvey 1996), high-resolution data are required in order to accurately determine the linear sizes of the starburst regions and the corresponding surface densities....
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...High-resolution HI observations are only available for a few of these galaxies, and in those cases the atomic fraction in the circumnuclear region is small, of order a few percent or less (e.g., Garcia-Barreto 1991; Downes et al. 1996; Sanders & Mirabel 1996)....
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TL;DR: The Copernicus satellite surveyed the spectral region near L alpha to obtain column densities of interstellar HI toward 100 stars as discussed by the authors, and the value of the mean ratio of total neutral hydrogen to color excess was found to equal 5.8 x 10 to the 21st power atoms per (sq cm x mag).
Abstract: The Copernicus satellite surveyed the spectral region near L alpha to obtain column densities of interstellar HI toward 100 stars. The distance to 10 stars exceeds 2 kpc and 34 stars lie beyond 1 kpc. Stars with color excess E(B-V) up to 0.5 mag are observed. The value of the mean ratio of total neutral hydrogen to color excess was found to equal 5.8 x 10 to the 21st power atoms per (sq cm x mag). For stars with accurate E(B-V), the deviations from this mean are generally less than a factor of 1.5. A notable exception is the dark cloud star, rho Oph. A reduction in visual reddening efficiency for the grains that are larger than normal in the rho Oph dark cloud probably explains this result. The conversion of atomic hydrogen into molecular form in dense clouds was observed in the gas to E(B-V) correlation plots. The best estimate for the mean total gas density for clouds and the intercloud medium, as a whole, in the solar neighborhood and in the plane of the galaxy is 1.15 atoms per cu. cm; those for the atomic gas and molecular gas alone are 0.86 atoms per cu cm and 0.143 molecules per cu cm respectively. For the intercloud medium, where molecular hydrogen is a negligible fraction of the total gas, atomic gas density was found to equal 0.16 atoms per cu cm with a Gaussian scale height perpendicular to the plane of about 350 pc, as derived from high latitude stars.
2,625 citations
2,251 citations
"The Global Schmidt law in star form..." refers background in this paper
...The most widely applied star formation law remains the simple gas density power law introduced by Schmidt (1959), which for external galaxies is usually expressed in terms of the observable surface densities of gas and star formation: Σ SF R = A Σ N gas (1) The validity of the Schmidt law has been…...
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TL;DR: In this article, the dependence of the massive star formation rate (SFR) on the density and dynamics of the interstellar gas was investigated in 15 galaxies and the relationship between the SFR and gas surface density was defined.
Abstract: Measurements of the distribution of H-alpha emission in galaxies are combined with published H I and CO data in order to reassess the dependence of the massive star formation rate (SFR) on the density and dynamics of the interstellar gas. The disk-averaged H-alpha surface brightness is correlated with the mean atomic and total gas surface densities, but is only weakly correlated with the mean molecular gas density inferred from CO emission. Radial profiles of gas and H-alpha emission in 15 galaxies are used to define the relationship between the SFR and gas surface density. In dense regions, the SFR and total gas density are well-represented by a Schmidt power-law relation. This Schmidt law breaks down, however, at densities below a critical threshold value. Massive star formation is completely suppressed at surface densities well below the threshold, while at densities near the threshold value the slope of the SFR-density relation is much steeper than a normal Schmidt law. A simple Toomre disk stability model predicts threshold densities and radii which are in excellent agreement with observations. 111 refs.
1,602 citations
"The Global Schmidt law in star form..." refers background in this paper
...On large scales the star formation law shows a more complex character, with a Schmidt law at high gas densities, and a sharp decline in the SFR below a critical threshold density (Kennicutt 1989, hereafter K89)....
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