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Jonathan C Tan - One of the best experts on this subject based on the ideXlab platform.
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gmc collisions as triggers of Star Formation vii the effect of magnetic field strength on Star Formation
The Astrophysical Journal, 2020Co-Authors: Jonathan C Tan, Duncan Christie, Fumitaka NakamuraAbstract:We investigate the Formation of Stars within giant molecular clouds (GMCs) evolving in environments of different global magnetic field strength and large-scale dynamics. Building upon a series of magnetohydrodynamic simulations of noncolliding and colliding GMCs, we employ density- and magnetically regulated Star Formation subgrid models in clouds that range from moderately magnetically supercritical to near critical. We examine gas and Star cluster morphologies, magnetic field strengths and relative orientations, prestellar core densities, temperatures, mass-to-flux ratios and velocities, Star Formation rates and efficiencies over time, spatial clustering of Stars, and kinematics of the Stars and natal gas. The large-scale magnetic criticality of the region greatly affects the overall gas evolution and Star Formation properties. GMC collisions enhance Star Formation rates and efficiencies in magnetically supercritical conditions, but may actually inhibit them in the magnetically critical case. This may have implications for Star Formation in different Galactic environments such as the Galactic Center and the main Galactic disk.
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molecular clouds internal properties turbulence Star Formation and feedback
arXiv: Astrophysics of Galaxies, 2012Co-Authors: Jonathan C Tan, Suzanne N Shaske, Sven Van LooAbstract:All Stars are born in molecular clouds, and most in giant molecular clouds (GMCs), which thus set the Star Formation activity of galaxies. We first review their observed properties, including measures of mass surface density, Sigma, and thus mass, M. We discuss cloud dynamics, concluding most GMCs are gravitationally bound. Star Formation is highly clustered within GMCs, but overall is very inefficient. We compare properties of Star-forming clumps with those of young stellar clusters (YSCs). The high central densities of YSCs may result via dynamical evolution of already-formed Stars during and after Star cluster Formation. We discuss theoretical models of GMC evolution, especially addressing how turbulence is maintained, and emphasizing the importance of GMC collisions. We describe how feedback limits total Star Formation efficiency, epsilon, in clumps. A turbulent and clumpy medium allows higher epsilon, permitting Formation of bound clusters even when escape speeds are less than the ionized gas sound speed.
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molecular clouds internal properties turbulence Star Formation and feedback
Proceedings of the International Astronomical Union, 2012Co-Authors: Jonathan C Tan, Suzanne N Shaske, Sven Van LooAbstract:All Stars are born in molecular clouds, and most in giant molecular clouds (GMCs), which thus set the Star Formation activity of galaxies. We first review their observed properties, including measures of mass surface density, �, and thus mass, M. We discuss cloud dynamics, concluding most GMCs are gravitationally bound. Star Formation is highly clustered within GMCs, but overall is very inefficient. We compare properties of Star-forming clumps with those of young stellar clusters (YSCs). The high central densities of YSCs may result via dynamical evolution of already-formed Stars during and after Star cluster Formation. We discuss theoretical models of GMC evolution, especially addressing how turbulence is maintained, and emphasizing the importance of GMC collisions. We describe how feedback limits total Star Formation effi- ciency, ǫ, in clumps. A turbulent and clumpy medium allows higher ǫ, permitting Formation of bound clusters even when escape speeds are less than the ionized gas sound speed.
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deuteration as an evolutionary tracer in massive Star Formation
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: F Fontani, Jonathan C Tan, Aina Palau, P Caselli, A Sanchezmonge, Michael J Butler, Izaskun Jimenezserra, Gemma Busquet, S LeuriniAbstract:Theory predicts, and observations confirm, that the column density ratio of a molecule containing D to its counterpart containing H can be used as an evolutionary tracer in the low-mass Star Formation process. Since it remains unclear if the high-mass Star Formation process is a scaled-up version of the low-mass one, we investigated whether the relation between deuteration and evolution can be applied to the high-mass regime. With the IRAM-30m telescope, we observed rotational transitions of N2D+ and N2H+ and derived the deuterated fraction in 27 cores within massive Star-forming regions understood to represent different evolutionary stages of the massive-Star Formation process. Results. Our results clearly indicate that the abundance of N2D+ is higher at the pre-stellar/cluster stage, then drops during the Formation of the protostellar object(s) as in the low-mass regime, remaining relatively constant during the ultra-compact HII region phase. The objects with the highest fractional abundance of N2D+ are Starless cores with properties very similar to typical pre-stellar cores of lower mass. The abundance of N2D+ is lower in objects with higher gas temperatures as in the low-mass case but does not seem to depend on gas turbulence. Our results indicate that the N2D+-to-N2H+ column density ratio can be used as an evolutionary indicator in both low- and high-mass Star Formation, and that the physical conditions influencing the abundance of deuterated species likely evolve similarly during the processes that lead to the Formation of both low- and high-mass Stars.
Mark R Krumholz - One of the best experts on this subject based on the ideXlab platform.
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a unified model for galactic discs Star Formation turbulence driving and mass transport
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: Mark R Krumholz, John C Forbes, Blakesley Burkhart, Roland M CrockerAbstract:We introduce a new model for the structure and evolution of the gas in galactic discs. In the model the gas is in vertical pressure and energy balance. Star Formation feedback injects energy and momentum, and non-axisymmetric torques prevent the gas from becoming more than marginally gravitationally unstable. From these assumptions we derive the relationship between galaxies' bulk properties (gas surface density, stellar content, and rotation curve) and their Star Formation rates, gas velocity dispersions, and rates of radial inflow. We show that the turbulence in discs can be powered primarily by Star Formation feedback, radial transport, or a combination of the two. In contrast to models that omit either radial transport or Star Formation feedback, the predictions of this model yield excellent agreement with a wide range of observations, including the Star Formation law measured in both spatially resolved and unresolved data, the correlation between galaxies' Star Formation rates and velocity dispersions, and observed rates of radial inflow. The agreement holds across a wide range of galaxy mass and type, from local dwarfs to extreme Starbursts to high-redshifts discs. We apply the model to galaxies on the Star-forming main sequence, and show that it predicts a transition from mostly gravity-driven turbulence at high redshift to Star Formation-driven turbulence at low redshift. This transition, and the changes in mass transport rates that it produces, naturally explain why galaxy bulges tend to form at high redshift and discs at lower redshift, and why galaxies tend to quench inside-out.
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the big problems in Star Formation the Star Formation rate stellar clustering and the initial mass function
Physics Reports, 2014Co-Authors: Mark R KrumholzAbstract:Abstract Star Formation lies at the center of a web of processes that drive cosmic evolution: generation of radiant energy, synthesis of elements, Formation of planets, and development of life. Decades of observations have yielded a variety of empirical rules about how it operates, but at present we have no comprehensive, quantitative theory. In this review I discuss the current state of the field of Star Formation, focusing on three central questions: What controls the rate at which gas in a galaxy converts to Stars? What determines how those Stars are clustered, and what fraction of the stellar population ends up in gravitationally-bound structures? What determines the stellar initial mass function, and does it vary with Star-forming environment? I use these three questions as a lens to introduce the basics of Star Formation, beginning with a review of the observational phenomenology and the basic physical processes. I then review the status of current theories that attempt to solve each of the three problems, pointing out links between them and opportunities for theoretical and numerical work that crosses the scale between them. I conclude with a discussion of prospects for theoretical progress in the coming years.
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the Star Formation law in molecule poor galaxies
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: Mark R KrumholzAbstract:In this paper, I investigate the processes that regulate the rate of Star Formation in regions of galaxies where the neutral interstellar medium is predominantly composed of non-Star-forming HI. In such regions, found today predominantly in low-metallicity dwarf galaxies and in the outer parts of large spirals, the Star Formation rate per unit area and per unit mass is much smaller than in more molecule-rich regions. While in molecule-rich regions the ultraviolet radiation field produced by efficient Star Formation forces the density of the cold neutral medium to a value set by two-phase equilibrium, I show that the low rates of Star Formation found in molecule-poor regions preclude this condition. Instead, the density of the cold neutral gas is set by the requirements of hydrostatic balance. Using this result, I extend the Krumholz, McKee, & Tumlinson model for Star Formation and the atomic to molecular transition to the molecule-poor regime. This "KMT+" model matches a wide range of observations of the Star Formation rate and the balance between the atomic and molecular phases in dwarfs and in the outer parts of spirals, and is well-suited to implementation as a subgrid recipe for Star Formation in cosmological simulations and semi-analytic models. I discuss the implications of this model for Star Formation over cosmological times.
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the Star Formation law in atomic and molecular gas
The Astrophysical Journal, 2009Co-Authors: Mark R Krumholz, Christopher F Mckee, Jason TumlinsonAbstract:We propose a simple theoretical model for Star Formation in which the local Star Formation rate (SFR) in a galaxy is determined by three factors. First, the interplay between the interstellar radiation field and molecular self-shielding determines what fraction of the gas is in molecular form and thus eligible to form Stars. Second, internal feedback determines the properties of the molecular clouds that form, which are nearly independent of galaxy properties until the galactic interstellar medium (ISM) pressure becomes comparable to the internal giant molecular cloud (GMC) pressure. Above this limit, galactic ISM pressure determines molecular gas properties. Third, the turbulence driven by feedback processes in GMCs makes Star Formation slow, allowing a small fraction of the gas to be converted to Stars per free-fall time within the molecular clouds. We combine analytic estimates for each of these steps to formulate a single Star Formation law, and show that the predicted correlation between SFR, metallicity, and surface densities of atomic, molecular, and total gas agree well with observations.
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the Star Formation law in atomic and molecular gas
arXiv: Astrophysics of Galaxies, 2009Co-Authors: Mark R Krumholz, Christopher F Mckee, Jason TumlinsonAbstract:We propose a simple theoretical model for Star Formation in which the local Star Formation rate in a galaxy is determined by three factors. First, the interplay between the interstellar radiation field and molecular self-shielding determines what fraction of the gas is in molecular form and thus eligible to form Stars. Second, internal feedback determines the properties of the molecular clouds that form, which are nearly independent of galaxy properties until the galactic ISM pressure becomes comparable to the internal GMC pressure. Above this limit, galactic ISM pressure determines molecular gas properties. Third, the turbulence driven by feedback processes in GMCs makes Star Formation slow, allowing a small fraction of the gas to be converted to Stars per free-fall time within the molecular clouds. We combine analytic estimates for each of these steps to formulate a single Star Formation law, and show that the predicted correlation between Star Formation rate, metallicity, and surface densities of atomic, molecular, and total gas agree well with observations.
Joao Alves - One of the best experts on this subject based on the ideXlab platform.
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schmidt s conjecture and Star Formation in molecular clouds
The Astrophysical Journal, 2013Co-Authors: Charles J Lada, M Lombardi, C Romanzuniga, Jan Forbrich, Joao AlvesAbstract:We investigate Schmidt's conjecture (i.e., that the Star Formation rate (SFR) scales in a power-law fashion with the gas density) for four well-studied local molecular clouds (giant molecular clouds, GMCs). Using the Bayesian methodology, we show that a local Schmidt scaling relation of the form (protoStars pc–2) exists within (but not between) GMCs. Further, we find that the Schmidt scaling law does not by itself provide an adequate description of Star Formation activity in GMCs. Because the total number of protoStars produced by a cloud is given by the product of Σ*(A K) and S'(> A K), the differential surface area distribution function, integrated over the entire cloud, the cloud's structure plays a fundamental role in setting the level of its Star Formation activity. For clouds with similar functional forms of Σ*(A K), observed differences in their total SFRs are primarily due to the differences in S'(> A K) between the clouds. The coupling of Σ*(A K) with the measured S'(> A K) in these clouds also produces a steep jump in the SFR and protostellar production above AK ~ 0.8 mag. Finally, we show that there is no global Schmidt law that relates the SFR and gas mass surface densities between GMCs. Consequently, the observed Kennicutt-Schmidt scaling relation for disk galaxies is likely an artifact of unresolved measurements of GMCs and not a result of any underlying physical law of Star Formation characterizing the molecular gas.
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schmidt s conjecture and Star Formation in molecular clouds
arXiv: Astrophysics of Galaxies, 2013Co-Authors: Charles J Lada, M Lombardi, C Romanzuniga, Jan Forbrich, Joao AlvesAbstract:We investigate Schmidt's conjecture (i.e., that the Star Formation rate scales in a power-law fashion with the gas density) for four well-studied local molecular clouds (GMCs). Using the Bayesian methodology we show that a local Schmidt scaling relation of the form Sigma*(A_K) = kappa x (A_K)^{beta} (protoStars pc^{-2}) exists within (but not between) GMCs. Further we find that the Schmidt scaling law, by itself, does not provide an adequate description of Star Formation activity in GMCs. Because the total number of protoStars produced by a cloud is given by the product of Sigma*(A_K) and S'(> A_K), the differential surface area distribution function, integrated over the entire cloud, the cloud's structure plays a fundamental role in setting the level of its Star Formation activity. For clouds with similar functional forms of Sigma*(A_K), observed differences in their total SFRs are primarily due to the differences in S'(> A_K) between the clouds. The coupling of Sigma*(A_K) with the measured S'(> A_K) in these clouds also produces a steep jump in the SFR and protostellar production above A_K ~ 0.8 magnitudes. Finally, we show that there is no global Schmidt law that relates the Star Formation rate and gas mass surface densities between GMCs. Consequently, the observed Kennicutt-Schmidt scaling relation for disk galaxies is likely an artifact of unresolved measurements of GMCs and not a result of any underlying physical law of Star Formation characterizing the molecular gas.
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Star Formation rates in molecular clouds and the nature of the extragalactic scaling relations
The Astrophysical Journal, 2012Co-Authors: Charles J Lada, M Lombardi, Jan Forbrich, Joao AlvesAbstract:In this paper, we investigate scaling relations between Star Formation rates and molecular gas masses for both local Galactic clouds and a sample of external galaxies. We specifically consider relations between the Star Formation rates and measurements of dense, as well as total, molecular gas masses. We argue that there is a fundamental empirical scaling relation that directly connects the local Star Formation process with that operating globally within galaxies. Specifically, the total Star Formation rate in a molecular cloud or galaxy is linearly proportional to the mass of dense gas within the cloud or galaxy. This simple relation, first documented in previous studies, holds over a span of mass covering nearly nine orders of magnitude and indicates that the rate of Star Formation is directly controlled by the amount of dense molecular gas that can be assembled within a Star Formation complex. We further show that the Star Formation rates and total molecular masses, characterizing both local clouds and galaxies, are correlated over similarly large scales of mass and can be described by a family of linear Star Formation scaling laws, parameterized by f DG, the fraction of dense gas contained within the clouds or galaxies. That is, the underlying Star Formation scaling law is always linear for clouds and galaxies with the same dense gas fraction. These considerations provide a single unified framework for understanding the relation between the standard (nonlinear) extragalactic Schmidt-Kennicutt scaling law, that is typically derived from CO observations of the gas, and the linear Star Formation scaling law derived from HCN observations of the dense gas.
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on the Star Formation rates in molecular clouds
The Astrophysical Journal, 2010Co-Authors: Charles J Lada, M Lombardi, Joao AlvesAbstract:In this paper, we investigate the level of Star Formation activity within nearby molecular clouds. We employ a uniform set of infrared extinction maps to provide accurate assessments of cloud mass and structure and compare these with inventories of young stellar objects within the clouds. We present evidence indicating that both the yield and rate of Star Formation can vary considerably in local clouds, independent of their mass and size. We find that the surface density structure of such clouds appears to be important in controlling both these factors. In particular, we find that the Star Formation rate (SFR) in molecular clouds is linearly proportional to the cloud mass (M 0.8) above an extinction threshold of A K ≈ 0.8 mag, corresponding to a gas surface density threshold of Σgas ≈ 116 M ☉ pc2. We argue that this surface density threshold corresponds to a gas volume density threshold which we estimate to be n(H2) ≈ 104 cm–3. Specifically, we find SFR (M ☉ yr–1) = 4.6 ± 2.6 × 10–8 M 0.8 (M ☉) for the clouds in our sample. This relation between the rate of Star Formation and the amount of dense gas in molecular clouds appears to be in excellent agreement with previous observations of both galactic and extragalactic Star-forming activity. It is likely the underlying physical relationship or empirical law that most directly connects Star Formation activity with interstellar gas over many spatial scales within and between individual galaxies. These results suggest that the key to obtaining a predictive understanding of the SFRs in molecular clouds and galaxies is to understand those physical factors which give rise to the dense components of these clouds.
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on the Star Formation rates in molecular clouds
arXiv: Astrophysics of Galaxies, 2010Co-Authors: Charles J Lada, M Lombardi, Joao AlvesAbstract:In this paper we investigate the level of Star Formation activity within nearby molecular clouds. We employ a uniform set of infrared extinction maps to provide accurate assessments of cloud mass and structure and compare these with inventories of young stellar objects within the clouds. We present evidence indicating that both the yield and rate of Star Formation can vary considerably in local clouds, independent of their mass and size. We find that the surface density structure of such clouds appears to be important in controlling both these factors. In particular, we find that the Star Formation rate (SFR) in molecular clouds is linearly proportional to the cloud mass (M_{0.8}) above an extinction threshold of A_K approximately equal to 0.8 magnitudes, corresponding to a gas surface density threshold of approximaely 116 solar masses per square pc. We argue that this surface density threshold corresponds to a gas volume density threshold which we estimate to be n(H_2) approximately equal to 10^4\cc. Specifically we find SFR (solar masses per yr) = 4.6 +/- 2.6 x 10^{-8} M_{0.8} (solar masses) for the clouds in our sample. This relation between the rate of Star Formation and the amount of dense gas in molecular clouds appears to be in excellent agreement with previous observations of both galactic and extragalactic Star forming activity. It is likely the underlying physical relationship or empirical law that most directly connects Star Formation activity with interstellar gas over many spatial scales within and between individual galaxies. These results suggest that the key to obtaining a predictive understanding of the Star Formation rates in molecular clouds and galaxies is to understand those physical factors which give rise to the dense components of these clouds.
Norman Murray - One of the best experts on this subject based on the ideXlab platform.
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self regulated Star Formation in galaxies via momentum input from massive Stars
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: Philip F Hopkins, Eliot Quataert, Norman MurrayAbstract:Feedback from massive Stars is believed to play a critical role in shaping the galaxy mass function, the structure of the interstellar medium (ISM) and the low efficiency of Star Formation, but the exact form of the feedback is uncertain. In this paper, the first in a series, we present and test a novel numerical implementation of stellar feedback resulting from momentum imparted to the ISM by radiation, supernovae and stellar winds. We employ a realistic cooling function, and find that a large fraction of the gas cools to ≲100 K, so that the ISM becomes highly inhomogeneous. Despite this, our simulated galaxies reach an approximate steady state, in which gas gravitationally collapses to form giant ‘molecular’ clouds (GMCs), dense clumps and Stars; subsequently, stellar feedback disperses the GMCs, repopulating the diffuse ISM. This collapse and dispersal cycle is seen in models of Small Magellanic Cloud (SMC)-like dwarfs, the Milky Way and z∼ 2 clumpy disc analogues. The simulated global Star Formation efficiencies are consistent with the observed Kennicutt–Schmidt relation. Moreover, the Star Formation rates are nearly independent of the numerically imposed high-density Star Formation efficiency, density threshold and density scaling. This is a consequence of the fact that, in our simulations, Star Formation is regulated by stellar feedback limiting the amount of very dense gas available for forming Stars. In contrast, in simulations without stellar feedback, i.e. under the action of only gravity and gravitationally induced turbulence, the ISM experiences runaway collapse to very high densities. In these simulations without feedback, the global Star Formation rates exceed observed galactic Star Formation rates by 1–2 orders of magnitude, demonstrating that stellar feedback is crucial to the regulation of Star Formation in galaxies.
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Star Formation efficiencies and lifetimes of giant molecular clouds in the milky way
The Astrophysical Journal, 2011Co-Authors: Norman MurrayAbstract:We use a sample of the 13 most luminous WMAP Galactic free-free sources, responsible for 33% of the free-free emission of the Milky Way, to investigate Star Formation. The sample contains 40 Star-forming complexes; we combine this sample with giant molecular cloud (GMC) catalogs in the literature to identify the host GMCs of 32 of the complexes. We estimate the Star Formation efficiency GMC and Star Formation rate per free-fall time ff. We find that GMC ranges from 0.002 to 0.2, with an ionizing luminosity-weighted average GMC Q = 0.08, compared to the Galactic average ≈0.005. Turning to the Star Formation rate per free-fall time, we find values that range up to . Weighting by ionizing luminosity, we find an average of ff Q = 0.14-0.24 depending on the estimate of the age of the system. Once again, this is much larger than the Galaxy-wide average value ff = 0.006. We show that the lifetimes of GMCs at the mean mass found in our sample is 27 ± 12 Myr, a bit less than three free-fall times. The GMCs hosting the most luminous clusters are being disrupted by those clusters. Accordingly, we interpret the range in ff as the result of a time-variable Star Formation rate; the rate of Star Formation increases with the age of the host molecular cloud, until the Stars disrupt the cloud. These results are inconsistent with the notion that the Star Formation rate in Milky Way GMCs is determined by the properties of supersonic turbulence.
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self regulated Star Formation in galaxies via momentum input from massive Stars
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Philip F Hopkins, Eliot Quataert, Norman MurrayAbstract:Feedback from massive Stars is believed to play a critical role in shaping the galaxy mass function, the structure of the interstellar medium (ISM), and the low efficiency of Star Formation, but the exact form of the feedback is uncertain. In this paper, the first in a series, we present and test a novel numerical implementation of stellar feedback resulting from momentum imparted to the ISM by radiation, supernovae, and stellar winds. We employ a realistic cooling function, and find that a large fraction of the gas cools to <100K, so that the ISM becomes highly inhomogeneous. Despite this, our simulated galaxies reach an approximate steady state, in which gas gravitationally collapses to form giant molecular clouds (GMCs), dense clumps, and Stars; subsequently, stellar feedback disperses the GMCs, repopulating the diffuse ISM. This collapse and dispersal cycle is seen in models of SMC-like dwarfs, the Milky-Way, and z~2 clumpy disk analogues. The simulated global Star Formation efficiencies are consistent with the observed Kennicutt-Schmidt relation. Moreover, the Star Formation rates are nearly independent of the numerically imposed high-density Star Formation efficiency, density threshold, and density scaling. This is a consequence of the fact that, in our simulations, Star Formation is regulated by stellar feedback limiting the amount of very dense gas available for forming Stars. In contrast, in simulations without stellar feedback, i.e. under the action of only gravity and gravitationally-induced turbulence, the ISM experiences runaway collapse to very high densities. In these simulations without feedback, the global Star Formation rates exceed observed galactic Star Formation rates by 1-2 orders of magnitude, demonstrating that stellar feedback is crucial to the regulation of Star Formation in galaxies.
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Star Formation efficiencies and lifetimes of giant molecular clouds in the milky way
arXiv: Astrophysics of Galaxies, 2010Co-Authors: Norman MurrayAbstract:We use a sample of the 13 most luminous WMAP Galactic free-free sources, responsible for 33% of the free- free emission of the Milky Way, to investigate Star Formation. The sample contains 40 Star forming complexes; we combine this sample with giant molecular cloud (GMC) catalogs in the literature, to identify the host GMCs of 32 of the complexes. We estimate the Star Formation efficiency epsilon_GMC and Star Formation rate per free-fall time epsilon_ff. We find that epsilon_GMC ranges from 0.002 to 0.2, with an ionizing luminosity-weighted average epsilon_GMC = 0.08, compared to the Galactic average = 0.005. Turning to the Star Formation rate per free-fall time, we find values that range up to epsilon_ff = 1. Weighting by ionizing luminosity, we find an average of epsilon_ff = 0.16 - 0.24 depending on the estimate of the age of the system. Once again, this is much larger than the Galaxy-wide average value epsilon_ff = 0.008. We show that the lifetimes of giant molecular clouds at the mean mass found in our sample is 17 plus or minus 4 Myr, about two free-fall times. The GMCs hosting the most luminous clusters are being disrupted by those clusters. Accordingly, we interpret the range in epsilon_ff as the result of a time-variable Star Formation rate; the rate of Star Formation increases with the age of the host molecular cloud, until the Stars disrupt the cloud. These results are inconsistent with the notion that the Star Formation rate in Milky Way GMCs is determined by the properties of supersonic turbulence
Volker Gaibler - One of the best experts on this subject based on the ideXlab platform.
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jet induced Star Formation in gas rich galaxies
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Martin Krause, Volker Gaibler, Sadegh Khochfar, Joseph SilkAbstract:Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of quenching cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the quenching of Star Formation. To shed more light on the actual physics of the ‘radio mode' part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc () of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit Star Formation model in the simulation. Following the system over more than 107 yr, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the Star Formation rate due to the Formation of a blast wave with strong compression and cooling in the ISM. This results in a ring- or disc-shaped population of young Stars. At later times, the increase in Star Formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed Stars may be up to for one duty cycle. We discuss the details of this jet-induced Star Formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.
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jet induced Star Formation in gas rich galaxies
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Martin Krause, Volker Gaibler, Sadegh Khochfar, Joseph SilkAbstract:Feedback from active galactic nuclei (AGN) has become a major component in simulations of galaxy evolution, in particular for massive galaxies. AGN jets have been shown to provide a large amount of energy and are capable of quenching cooling flows. Their impact on the host galaxy, however, is still not understood. Subgrid models of AGN activity in a galaxy evolution context so far have been mostly focused on the quenching of Star Formation. To shed more light on the actual physics of the "radio mode" part of AGN activity, we have performed simulations of the interaction of a powerful AGN jet with the massive gaseous disc (10^11 solar masses) of a high-redshift galaxy. We spatially resolve both the jet and the clumpy, multi-phase interstellar medium (ISM) and include an explicit Star Formation model in the simulation. Following the system over more than 10^7 years, we find that the jet activity excavates the central region, but overall causes a significant change to the shape of the density probability distribution function and hence the Star Formation rate due to the Formation of a blast wave with strong compression and cooling in the ISM. This results in a ring- or disc-shaped population of young Stars. At later times, the increase in Star Formation rate also occurs in the disc regions further out since the jet cocoon pressurizes the ISM. The total mass of the additionally formed Stars may be up to 10^10 solar masses for one duty cycle. We discuss the details of this jet-induced Star Formation (positive feedback) and its potential consequences for galaxy evolution and observable signatures.