scholarly journals Accretion bursts in low-metallicity protostellar disks

2020 ◽  
Vol 641 ◽  
pp. A72
Author(s):  
Eduard I. Vorobyov ◽  
Vardan G. Elbakyan ◽  
Kazuyuki Omukai ◽  
Takashi Hosokawa ◽  
Ryoki Matsukoba ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Gravitational Instability ◽  
Mass Loading ◽  
Protostellar Disks ◽  
Numerical Hydrodynamics ◽  
Accretion Rates ◽  
Solar Metallicity ◽  
Disk Evolution ◽  
Low Metallicity ◽  
Cloud Cores

Aims. The early evolution of protostellar disks with metallicities in the Z = 1.0 − 0.01 Z⊙ range was studied with a particular emphasis on the strength of gravitational instability and the nature of protostellar accretion in low-metallicity systems. Methods. Numerical hydrodynamics simulations in the thin-disk limit were employed that feature separate gas and dust temperatures, and disk mass-loading from the infalling parent cloud cores. Models with cloud cores of similar initial mass and rotation pattern but distinct metallicity were considered to distinguish the effect of metallicity from that of the initial conditions. Results. The early stages of disk evolution in low-metallicity models are characterized by vigorous gravitational instability and fragmentation. Disk instability is sustained by continual mass-loading from the collapsing core. The time period that is covered by this unstable stage is much shorter in the Z = 0.01 Z⊙ models than in their higher metallicity counterparts thanks to the higher rates of mass infall caused by higher gas temperatures (which decouple from lower dust temperatures) in the inner parts of collapsing cores. Protostellar accretion rates are highly variable in the low-metallicity models reflecting the highly dynamic nature of the corresponding protostellar disks. The low-metallicity systems feature short but energetic episodes of mass accretion caused by infall of inward-migrating gaseous clumps that form via gravitational fragmentation of protostellar disks. These bursts seem to be more numerous and last longer in the Z = 0.1 Z⊙ models than in the Z = 0.01 Z⊙ case. Conclusions. Variable protostellar accretion with episodic bursts is not a particular feature of solar metallicity disks. It is also inherent to gravitationally unstable disks with metallicities up to 100 times lower than solar.

scholarly journals Embedded disks around low-mass protostars

2010 ◽  
Vol 6 (S270) ◽  
pp. 219-222
Author(s):  
Eduard I. Vorobyov ◽  
Shantanu Basu
Keyword(s):  
Core Mass ◽  
Multiple Systems ◽  
Protostellar Disks ◽  
Numerical Hydrodynamics ◽  
Accretion Rates ◽  
Low Mass ◽  
Sizeable Fraction ◽  
Phase Systems ◽  
Cloud Cores ◽  
Embedded Disks

AbstractThe time evolution of protostellar disks in the embedded phase of star formation (EPSF) is reviewed based on numerical hydrodynamics simulations of the gravitational collapse of two cloud cores with distinct initial masses. Special emphasis is given to disk, stellar, and envelope masses and also mass accretion rates onto the star. It is shown that accretion is highly variable in the EPSF, in agreement with recent theoretical and observational expectations. Protostellar disks quickly accumulate mass upon formation and may reach a sizeable fraction of the envelope mass (~35%) by the end of the Class 0 phase. Systems with disk-to-star mass ratio ξ≈0.5 are common but systems with ξ≥1.0 are rare because the latter quickly evolve into binary or multiple systems. Embedded disks are characterized by radial pulsations, the amplitude of which increases with growing core mass.

scholarly journals Mg II λ2797, λ2803 emission in a large sample of low-metallicity star-forming galaxies from SDSS DR14

2019 ◽  
Vol 624 ◽  
pp. A21 ◽  
Author(s):  
N. G. Guseva ◽  
Y. I. Izotov ◽  
K. J. Fricke ◽  
C. Henkel
Keyword(s):  
Noble Gas ◽  
Formation Rate ◽  
Sloan Digital Sky Survey ◽  
Large Sample ◽  
Star Forming ◽  
Magnesium Depletion ◽  
Sky Survey ◽  
Solar Metallicity ◽  
Low Metallicity ◽  
Damped Lyman Alpha Systems

A large sample of Mg II emitting star-forming galaxies with low metallicity [O/H] = log(O/H) – log(O/H)⊙ between –0.2 and –1.2 dex is constructed from Data Release 14 of the Sloan Digital Sky Survey. We selected 4189 galaxies with Mg II λ2797, λ2803 emission lines in the redshift range z ∼ 0.3–1.0 or 35% of the total Sloan Digital Sky Survey star-forming sample with redshift z ≥ 0.3. We study the dependence of the magnesium-to-oxygen and magnesium-to-neon abundance ratios on metallicity. Extrapolating this dependence to [Mg/Ne] = 0 and to solar metallicity we derive a magnesium depletion of [Mg/Ne] ≃ –0.4 (at solar metallicity). We prefer neon instead of oxygen to evaluate the magnesium depletion in the interstellar medium because neon is a noble gas and is not incorporated into dust, contrary to oxygen. Thus, we find that more massive and more metal abundant galaxies have higher magnesium depletion. The global parameters of our sample, such as the mass of the stellar population and star formation rate, are compared with previously obtained results from the literature. These results confirm that Mg II emission has a nebular origin. Our data for interstellar magnesium-to-oxygen abundance ratios relative to the solar value are in good agreement with similar measurements made for Galactic stars, for giant stars in the Milky Way satellite dwarf galaxies, and with low-metallicity damped Lyman-alpha systems.

scholarly journals GRAVITY HEATS THE UNIVERSE

2009 ◽  
Vol 18 (14) ◽  
pp. 2201-2207
Author(s):  
ADAM MOSS ◽  
DOUGLAS SCOTT
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Energy Conservation ◽  
Cosmic Microwave Background ◽  
Initial Conditions ◽  
Gravitational Instability ◽  
Simplified Model ◽  
Microwave Background ◽  
Average Temperature ◽  
The Universe

Structures in the Universe grew through gravitational instability from very smooth initial conditions. Energy conservation requires that the growing negative potential energy of these structures be balanced by an increase in kinetic energy. A fraction of this is converted into heat in the collisional gas of the intergalactic medium. Using a toy model of gravitational heating, we attempt to link the growth of structure in the Universe with the average temperature of this gas. We find that the gas is rapidly heated from collapsing structures at around z ~ 10, reaching a temperature > 106 K today, depending on some assumptions of our simplified model. Before that there was a cold era from z ~ 100 to ~10 in which the matter temperature was below that of the cosmic microwave background.

scholarly journals The Structure of Cold Molecular Cloud Cores

2004 ◽  
Vol 221 ◽  
pp. 43-50
Author(s):  
D. Ward-Thompson ◽  
D. J. Nutter ◽  
J. M. Kirk ◽  
P. André
Keyword(s):  
Molecular Cloud ◽  
Initial Conditions ◽  
Current Knowledge ◽  
Current Debate ◽  
Core Density ◽  
Density Profiles ◽  
Cloud Cores ◽  
Protostellar Collapse ◽  
The Magnetic Field ◽  
Equilibrium Status

A brief summary is presented of our current knowledge of the structure of cold molecular cloud cores that do not contain protostars, sometimes known as starless cores. The most centrally condensed starless cores are known as pre-stellar cores. These cores probably represent observationally the initial conditions for protostellar collapse that must be input into all models of star formation. The current debate over the nature of core density profiles is summarised. A cautionary note is sounded over the use of such profiles to ascertain the equilibrium status of cores. The magnetic field structure of pre-stellar cores is also briefly discussed.

scholarly journals Jsolated Stars of Low Metallicity

Galaxies ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 89
Author(s):  
Efrat Sabach
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Luminosity Function ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Solar Metallicity ◽  
Low Metallicity ◽  
Low Mass

We study the effects of a reduced mass-loss rate on the evolution of low metallicity Jsolated stars, following our earlier classification for angular momentum (J) isolated stars. By using the stellar evolution code MESA we study the evolution with different mass-loss rate efficiencies for stars with low metallicities of Z = 0 . 001 and Z = 0 . 004 , and compare with the evolution with solar metallicity, Z = 0 . 02 . We further study the possibility for late asymptomatic giant branch (AGB)—planet interaction and its possible effects on the properties of the planetary nebula (PN). We find for all metallicities that only with a reduced mass-loss rate an interaction with a low mass companion might take place during the AGB phase of the star. The interaction will most likely shape an elliptical PN. The maximum post-AGB luminosities obtained, both for solar metallicity and low metallicities, reach high values corresponding to the enigmatic finding of the PN luminosity function.

scholarly journals Theoretical considerations for star formation at low and high redshift

2015 ◽  
Vol 11 (S315) ◽  
pp. 247-253
Author(s):  
Bruce G. Elmegreen
Keyword(s):  
Star Formation ◽  
Mass Density ◽  
High Redshift ◽  
Distribution Functions ◽  
High Mass ◽  
Formation Processes ◽  
Accretion Rates ◽  
Major Merger ◽  
Cloud Cores ◽  
Self Gravity

AbstractStar formation processes in strongly self-gravitating cloud cores should be similar at all redshifts, forming single or multiple stars with a range of masses determined by local magneto-hydrodynamics and gravity. The formation processes for these cores, however, as well as their structures, temperatures, Mach numbers, etc., and the boundedness and mass distribution functions of the resulting stars, should depend on environment, as should the characteristic mass, density, and column density at which cloud self-gravity dominates other forces. Because the environments for high and low redshift star formation differ significantly, we expect the resulting gas to stellar conversion details to differ also. At high redshift, the universe is denser and more gas-rich, so the active parts of galaxies are denser and more gas rich too, leading to slightly shorter gas consumption timescales, higher cloud pressures, and denser, more massive, bound stellar clusters at the high mass end. With shorter consumption times corresponding to higher relative cosmic accretion rates, and with the resulting higher star formation rates and their higher feedback powers, the ISM has greater turbulent speeds relative to the rotation speeds, thicker gas disks, and larger cloud and star complex sizes at the characteristic Jeans length. The result is a more chaotic appearance at high redshift, bridging the morphology gap between today's quiescent spirals and today's major-mergers, with neither spiral nor major-merger processes actually in play at that time. The result is also a thick disk at early times, and after in-plane accretion from relatively large clump torques, a classical bulge. Today's disks are thinner, and torque-driven accretion is slower outside of inner barred regions. This paper reviews the basic processes involved with star formation in order to illustrate its evolution over time and environment.

scholarly journals The Formation of Galaxies in Friedmannian Universes

1974 ◽  
Vol 63 ◽  
pp. 213-225 ◽  
Author(s):  
A. G. Doroshkevich ◽  
R. A. Sunyaev ◽  
Ya. B. Zel'Dovich
Keyword(s):  
Linear Theory ◽  
Initial Conditions ◽  
Gravitational Instability ◽  
Short Review ◽  
Clusters Of Galaxies ◽  
Non Linear

A short review of the theory of the formation of galaxies and clusters of galaxies is given within the framework of the non-linear theory of gravitational instability. Probable initial conditions are discussed as well as processes which bring about the origin of galaxies and clusters of galaxies. Possible observational tests are discussed.

scholarly journals Self-Similar Gravitational Clustering

1983 ◽  
Vol 104 ◽  
pp. 393-400
Author(s):  
G. Efstathiou
Keyword(s):  
Initial Conditions ◽  
Gravitational Instability ◽  
Early Time ◽  
Density Parameter ◽  
Small Perturbations ◽  
Gravitational Clustering ◽  
Point Correlation ◽  
Point Correlation Function ◽  
Similarity Scaling ◽  
Clustering Pattern

The nature of the distribution of galaxies poses a challenging problem for theorists. It seems reasonable, as a start, to suppose that galaxies and clusters arose from small perturbations by gravitational instability. However, one still has the problem of the choice of initial conditions, for example, the shape of the fluctuation spectrum and the cosmological density parameter Ω. A considerable simplification is to assume that the clustering pattern obeys some simple similarity scaling, so that the clustering at some early time, apart from a change in length scale, is statistically indistinguishable from the pattern observed today. The power-law shape of the two-point correlation function and the simple forms of higher order correlation functions (Peebles, 1980) have provided some evidence that such a simplifying assumption may be relevant - just how relevant is the subject of this article.

scholarly journals Effects of metallicity on high-mass X-ray binary formation

2019 ◽  
Vol 491 (3) ◽  
pp. 3606-3612 ◽  
Author(s):  
S Ponnada ◽  
M Brorby ◽  
P Kaaret
Keyword(s):  
Luminosity Function ◽  
Statistical Significance ◽  
Formation Rate ◽  
High Mass ◽  
X Ray ◽  
Binary Formation ◽  
Different Types ◽  
Solar Metallicity ◽  
Low Metallicity ◽  
X Ray Binaries

ABSTRACT The heating of the intergalactic medium in the early, metal-poor Universe may have been partly due to radiation from high-mass X-ray binaries (HMXBs). Previous investigations on the effect of metallicity have used galaxies of different types. To isolate the effects of metallicity on the production of HMXBs, we study a sample consisting only of 46 blue compact dwarf galaxies covering metallicity in the range 12+log(O/H) of 7.15–8.66. To test the hypothesis of metallicity dependence in the X-ray luminosity function (XLF), we fix the XLF form to that found for near-solar metallicity galaxies and use a Bayesian method to constrain the XLF normalization as a function of star formation rate for three different metallicity ranges in our sample. We find an increase by a factor of 4.45 ± 2.04 in the XLF normalization between the metallicity ranges 7.1–7.7 and 8.2–8.66 at a statistical significance of 99.79 per cent. Our results suggest that HMXB production is enhanced at low metallicity, and consequently that HMXBs may have contributed significantly to the reheating of the early Universe.

scholarly journals Gas inflow and star formation near supermassive black holes: the role of nuclear activity

2019 ◽  
Vol 489 (1) ◽  
pp. 52-77
Author(s):  
Christopher C Frazer ◽  
Fabian Heitsch
Keyword(s):  
Star Formation ◽  
Gravitational Instability ◽  
Numerical Models ◽  
Three Dimensional ◽  
Lower Surface ◽  
Nuclear Activity ◽  
Radiation Fields ◽  
Accretion Rates ◽  
Inflow Event ◽  
Uv Photons

ABSTRACT Numerical models of gas inflow towards a supermassive black hole (SMBH) show that star formation may occur in such an environment through the growth of a gravitationally unstable gas disc. We consider the effect of nuclear activity on such a scenario. We present the first three-dimensional grid-based radiative hydrodynamic simulations of direct collisions between infalling gas streams and a 4 × 106 M⊙ SMBH, using ray-tracing to incorporate radiation consistent with an active galactic nucleus (AGN). We assume inflow masses of ≈105 M⊙ and explore radiation fields of 10 per cent and 100 per cent of the Eddington luminosity (Ledd). We follow our models to the point of central gas disc formation preceding star formation and use the Toomre Q parameter (QT) to test for gravitational instability. We find that radiation pressure from UV photons inhibits inflow. Yet, for weak radiation fields, a central disc forms on time-scales similar to that of models without feedback. Average densities of >108 cm−3 limit photoheating to the disc surface allowing for QT ≈ 1. For strong radiation fields, the disc forms more gradually resulting in lower surface densities and larger QT values. Mass accretion rates in our models are consistent with 1–60 per cent of the Eddington limit, thus we conclude that it is unlikely that radiative feedback from AGN activity would inhibit circumnuclear star formation arising from a massive inflow event.

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