28 research outputs found
Relocationλ²κ³Ό λ³μ μ μμλ₯Ό μ΄μ©ν μ ν μμ μλ μ¬λΆν κ³Ό μ¬ν μ€μ°¨ νκ°μ κ΄ν μ°κ΅¬
νμλ
Όλ¬Έ(μμ¬)--μμΈλνκ΅ λνμ :μ‘°μ ν΄μ곡νκ³Ό,1996.Maste
λ§λμν ν΅κ³ 리μ λ³ νμ±
νμλ
Όλ¬Έ(λ°μ¬) -- μμΈλνκ΅λνμ : μμ°κ³Όνλν 물리·μ²λ¬ΈνλΆ(μ²λ¬Ένμ 곡), 2022. 8. κΉμ
ν.ν΅κ³ 리λ λ§λμν μ€μ¬μμ νν λ°κ²¬λλ κ³ λ¦¬ ννμ ꡬ쑰물μ΄λ€. ν΅κ³ 리λ λμ²΄λ‘ λ³νμμ΄ νλ°ν μΌμ΄λλ μ§μμ΄λ©°, μμ ν¬κΈ° (βΌ 1 kpc) μλ λΆκ΅¬νκ³ μν μ 체μ λ§λ¨Ήλ λ³νμ±λ₯ μ 보μ¬μ£ΌκΈ°λ νλ€. μν μ€μ¬μμ μ§μ€μ μΌλ‘ μΌμ΄λλ μ΄ λ¬ν λ³νμ±μ μ μ¬ν½λλΆλ₯Ό λΉλ‘―ν μ€μ¬λΆ κ³ λ°λ νμ± κ΅¬μ‘°λ¬Όλ€μ κΈ°μκ³Ό κ΄λ ¨μ΄ μλ€κ³ μ¬κ²¨μ§λ€. λν ν΅κ³ 리μ νλ°ν λ³νμμΌλ‘λΆν° λΉλ‘―λ 볡μ¬, νμ±ν, μ΄μ μ± νλ° λ±κ³Ό κ°μ λλ¨Ήμ μμ©μ μννμ νμ±μ΄λ μνν΅μ νλμ±μλ μν₯μ λ―ΈμΉ κ²μΌλ‘ μκ°λλ€. κ΄μΈ‘μ μΌλ‘ ν΅κ³ 리μ λ³νμ±λ₯ μ λ€μν μκ°μ²λμ μ§νμ κ°μ§ κ³ λ³νν΄ μ¨ κ²μΌλ‘ 보μ΄λλ°, 무μμ΄ ν΅κ³ 리μ λ³νμ±λ₯ μ κ²°μ νλ©° κ·Έκ²μ μκ°μ λ³νλ₯Ό μΌκΈ°νλμ§μ λν μ΄λ‘ μ μ΄ν΄λ λ―Έμ§νλ€. μ΄μ λ³Έ νμλ
Όλ¬Έμμλ 3μ°¨μ μκΈ°μ 체μνμ μμΉλͺ¨μμ€νμ ν΅νμ¬ ν΅κ³ 리μ λ³νμ±λ₯ μ μ€μν μν₯μ μ€ κ²μΌ λ‘ μκ°λλ μ§λ μ μ
λ₯ κ³Ό μ΄μ μ± λλ¨Ήμ λ° μκΈ°μ₯μ ν¨κ³Όλ₯Ό λ¨κ³μ μΌλ‘ μ΄ν΄λ³΄κ³ μ΄λ₯Ό ν΅ν΄ ν΅κ³ 리μ λ³νμ±λ₯ μ μ‘°μ νλ 물리μ κΈ°μμ λ°νκ³ μ νμλ€.
μ 2μ₯μμλ λ³Έ νμλ
Όλ¬Έμμ μ¬μ©ν μ€κ΄μ λͺ¨νμ μκ°νκ³ μ΄λ₯Ό μ΄μ©νμ¬ μ§ λ μ μ
λ₯ μ μΌμ νκ² ν΅μ νμ κ²½μ°μ ν΅κ³ 리μ λ³νμ±μ΄ μ΄λ€ μμμΌλ‘ μΌμ΄λλμ§ μμ보μλ€. λ€μν ν¬κΈ°μ μ§λ μ μ
λ₯ μ κ°λ λͺ¨νλ€μ λνμ¬ 3μ°¨μ μ 체μνμ μμΉλͺ¨μμ€νμ μνν κ²°κ³Ό ν΅κ³ 리μ λ³νμ±λ₯ μ κ³ λ¦¬μ ν¬κΈ°μλ 무κ΄νλ©° μ§λ μ μ
λ₯ κ³Ό κ°ν μκ΄κ΄κ³λ₯Ό 보μΈλ€λ κ²μ λ°κ²¬νμλ€. ν΅κ³ 리μ λ³νμ±λ₯ μ μ½ 2λ°° λ΄μΈμ 무μμμ μλμ μ μΈνλ©΄ λͺ¨λ κ²½μ° μκ°μ λ°λΌ μΌμ νκ² μ μ§λμλλ° μ΄λ κ΄μΈ‘λλ ν΅κ³ 리 λ³νμ±λ₯ μ μκ°μ λ°λ₯Έ λ³νλ₯Ό μ΄μ μ± λλ¨Ήμμ ν¨κ³Όλ§μΌλ‘ μ€λͺ
ν μ μμμ μμ¬νλ€. ν΅κ³ 리μ λ³νμ±λ₯ μ΄ μ§λ μ μ
λ₯ μ μν΄ κ²°μ λλ λ°λ©΄, ν΅κ³ 리μ 기체 μ§λμ λλ¨Ήμμ μν μ€μ¬λ©΄ μλ ₯μ΄ μ€μ¬λ©΄ μμͺ½μ λμΈ κΈ°μ²΄μ 무κ²μ μ μνμ ννμ μ΄λ£¨λ κ³Όμ μμ κ²°μ λμλ€.
μ 3μ₯μμλ μ§λ μ μ
λ₯ μ΄ μκ°μ λ°λΌ λ³ννκ±°λ λΉλμΉμ μΌ κ²½μ° ν΅κ³ 리μ λ³νμ±μ΄ μ΄λ ν μμμΌλ‘ μΌμ΄λ κ²μΈμ§ μμ보μλ€. μ§λ μ μ
λ₯ μ λ³ν μ£ΌκΈ°κ° λ 무 짧μ (< 50 Myr) κ²½μ°λ₯Ό μ μΈνλ©΄ ν΅κ³ 리μ λ³νμ±λ₯ μ μ½κ°μ μμ°¨λ₯Ό λκ³ μ§λ μ μ
λ₯ μ λ°λΌ λ³ννμλ€. λ³νμ±λ₯ μ λ³νμ λ°λΌ μ€μ¬λ©΄ μλ ₯κ³Ό 기체 λ¬΄κ² μμ μ κ°μ λ°λΌ λ³ννμμ§λ§ μ§λ μ μ
λ₯ μ΄ μΌμ ν κ²½μ°μ λ§μ°¬κ°μ§λ‘ μμ§ λ°©ν₯ μ μνμ ννμ νμ μ μ μ§λμλ€. λ³νμ±λ₯ κ³Ό 기체 μ§λμ κ΄κ³λ PRFMμ΄λ‘ μ΄ μμΈ‘νλ λ°μ μ λΆν©νμλ€. λΉλμΉμ μΈ μ§λ μ μ
μ΄ νμ λΉλμΉμ μΈ λ³νμ±μ μΌμΌν€μ§λ μμΌλ, λ λ¨Όμ§λ (dust lane) μ€ ν μͺ½μ μ§λ μ μ
λ₯ μ΄ κ°μκΈ° μ¦κ°νλ κ²½μ°μλ μΌμμ μΌλ‘ λΉλμΉμ λ³νμ±μ΄ μΌμ΄λ μ μμμ 보μλ€.
μ 4μ₯μμλ μκΈ°μ₯μ΄ ν΅κ³ 리μ μνμ μ§νμ λ³νμ±μ λ―ΈμΉλ μν μ μμ보기 μνμ¬ μμ μ¬μ©ν μ€κ΄μ λͺ¨νμ λ°μ μμΌ μκΈ°μ₯μ ν¬ν¨ν μ§λ μ μ
μ λ€λ£° μ μκ² νμλ€. λ€μν μ΄κΈ° μκΈ°μ₯μ κ°λ λͺ¨νμ λν΄ 3μ°¨μ μκΈ°μ 체μνμ μμΉλͺ¨μ μ€νμ μνν κ²°κ³Ό μκΈ°μ₯μ΄ ν΅κ³ 리 μμμμ λΉ λ₯΄κ² μ¦νλ¨μ λ°κ²¬νμλλ°, μ΄λ μ΄μ μ± λλ¨Ήμκ³Ό μ°¨λ±νμ μ΄ ν¨κ» μμ©ν κ²°κ³ΌλΌκ³ μκ°λλ€. μ°μ΄μ μ΄μ μ± νλ°μ μν΄ λ§λ€μ΄μ§ μ΄κ±°ν(superbubble)μ μ€μ¬λ©΄ 기체측μ λ«κ³ λμ κ³ λλ‘ ν½μ°½νλ κ³Όμ μμ κ³ λ¦¬ μμμ μν(toroidal) μκΈ°μ₯μ λκ³ λκ° μμ€λ©΄(poloidal) μκΈ°μ₯μ μμ±νμλ€. μκΈ°μλ ₯μ μ΄μ μλ ₯κ³Ό λλ₯μ μν μ΄λνμ μλ ₯μ λ₯κ°νμ¬ μ’
κ΅μ λ ν΅κ³ 리μ λ³νμ±λ₯ μ λ¨μ΄νΈλ Έλ€. μκΈ°μ₯λ ₯(magnetic tension)μ μν λλ¦Όνμ 기체μ κ°μ΄λλμ λΉΌμμ ν΅κ³ 리λ‘λΆν° μ€μ¬λ°©ν₯μΌλ‘μ κ°μ°© νλ¦μ μΌκΈ°νμ¬ ν΅μ£Ό λ³μλ°(circumnuclear disk)μ νμ±νμλ€.
μ΄λ¬ν κ²°κ³Όλ€μ μ’
ν©ν΄ λ³Ό λ ν΅κ³ 리μ λ³νμ±λ₯ μ΄ κΈ΄ μκ° κ°κ²© λμ λ³νν λ κ²μ μ£Όλ‘ μ§λ μ μ
λ₯ μ λ³νμ κΈ°μΈνλ κ²μ΄λ©°, μ΄μ μ± λλ¨Ήμμ λΉκ΅μ μμ μ§νκ³Ό μκ°μ²λλ₯Ό κ°λ 무μμμ μλμ μΌμΌν€λ ννΈ μμ§ λ°©ν₯ μ μνμ ννμ μ μ§ν¨μΌλ‘μ κ³ κ°μκ°μ κ²°μ νλ μν μ νλ€κ³ κ²°λ‘ μ§μ μ μμλ€. λ¨, μκΈ°μ₯μ΄ μμ£Ό κ°ν ν΅κ³ 리μ κ²½μ° λ³νμ±λ₯ μ΄ μ§λ μ μ
λ₯ λ³΄λ€ λ§€μ° μμμ§ μ μμ΄μ λ³νμ± λ₯ κ³Ό μ§λ μ μ
λ₯ μ κ΄κ³λ₯Ό λ€μ 볡μ‘νκ² λ§λ€ μ μμΌλ―λ‘ μΆν μ΄μ λν λ λ§μ μ°κ΅¬κ° μ΄λ£¨μ΄μ ΈμΌ ν κ²μ΄λ€.Nuclear rings are sites of compact yet intense star formation often found at centers of barred galaxies. Concentrated in a small volume, rapid formation of stars in nuclear rings has an important consequence on the buildup of dense stellar structures at galaxy centers. In addition, strong stellar feedback from nuclear rings greatly changes gas flow structure, affecting the launching of galactic winds and the fueling of nuclear activities. While observations indicate that the star formation rate of nuclear rings varies considerably with space and time, theoretical understanding of what controls star formation in nuclear rings remains elusive. In this thesis, we use three-dimensional (magneto)hydrodynamic simulations to investigate effects of mass inflow, supernova feedback, and magnetic fields on star formation in nuclear rings.
In Chapter 2, we use controlled numerical simulations to study what determines the structure and star formation rate of nuclear rings subject to constant mass inflow rates. A common numerical framework that is used throughout the thesis is introduced in this chapter. We find that, contrary to previous expectations based on one-dimensional models, the supernova feedback is not strong enough to destroy the ring or quench star formation everywhere in the ring because of their stochasticity in space and time. Under the constant mass inflow rate, the ring star formation is very steady and persistent, where the star formation rate is tightly correlated with the inflow rate and exhibits only mild temporal fluctuations. The ring gas mass at the given star formation rate is set by the force balance between the midplane pressure arising from stellar feedback and the weight of the gas under the gravitational field arising from both gas and stars.
In Chapter 3, we allow the mass inflow rate to vary in time and/or be asymmetric in space, to assess resulting effects on temporal and spatial distribution of star formation in nuclear rings. We find that a time-varying inflow rate with not too small an amplitude and timescale can cause episodic star formation in nuclear rings, such that the star formation rate follows the variation of the inflow rate with some time delay. Within the ring, vertical dynamical equilibrium is well maintained such that the midplane pressure balances the weight of the overlying gas, despite large time variations in the latter two quantities. The relation between the star formation rate and gas mass is consistent with the prediction from the pressure-regulated, feedback-modulated star formation theory. While asymmetry in the inflow rate does not necessarily lead to asymmetric star formation, a transient period of lopsided star formation occurs when the inflow rate from one of the two dust lanes is suddenly increased by a large factor.
In Chapter 4, we include magnetic fields in our models to study their effects on dynamical evolution of nuclear rings and star formation therein. We find that magnetic fields are efficiently amplified in the ring due presumably to rotational shear and supernova feedback. Expanding superbubbles created by clusterd supernova explosions drag predominantly-toroidal fields near the midplane to produce poloidal fields away in high-altitude regions. Magnetic pressure in the ring eventually dominates the thermal and turbulent pressures and suppresses the ring star formation. Strong magnetic tension in the ring drives accretion flows from the ring radially inward and forms a circumnuclear disk in the central region, which is absent in the unmagnetized model.
Taken together, we conclude that the ring star formation rate and its long-term time variations are causally controlled by the mass inflow rate, while the supernova feedback is responsible for maintaining the vertical dynamical equilibrium and by doing so setting the depletion time, and induces small-amplitude, short-term fluctuations in the star formation rate. When magnetic fields are very strong, however, the ring star formation rate can be significantly suppressed below the mass inflow rate, complicating the relation between the inflow rate and star formation rate.1 Introduction 1
1.1 Observational Evidence of Bar-Driven Galaxy Evolution 2
1.1.1 Central Star Formation Enhancements 3
1.1.2 Disk-Like Bulges 5
1.2 Gas Flow in Barred Galaxies 6
1.2.1 Closed Orbits 6
1.2.2 Gaseous Response 13
1.3 Nuclear Rings 16
1.3.1 Formation Mechanisms 16
1.3.2 Physical Properties 20
1.3.3 Star Formation History 23
1.4 Scope and Outline of This Thesis 24
2 Semi-Global Numerical Simulations of Nuclear Rings Subject to Constant Mass Inflow Rates 27
2.1 Overview 27
2.2 Numerical Methods 31
2.2.1 Basic Equations 31
2.2.2 Gas Inflow Streams 37
2.2.3 Star Particles and SN Feedback 40
2.2.4 Models 41
2.3 Evolution 44
2.3.1 Overall Evolution of the Fiducial Model 44
2.3.2 Star Formation 52
2.3.3 Other Models 55
2.4 Correlations of Statistical Quantities 60
2.4.1 Ring Properties 62
2.4.2 Vertical Dynamical Equilibrium and Star Formation Feedback 65
2.5 Summary and Discussion 77
2.5.1 Summary 77
2.5.2 Discussion 81
3 Effects of Varying Mass Inflows on Star Formation in Nuclear Rings 87
3.1 Overview 87
3.2 Methods 90
3.2.1 Equations 90
3.2.2 Models 93
3.3 Results 95
3.3.1 Time Variation of the SFR 97
3.3.2 Relation between the SFR and the Inflow Rate 98
3.3.3 Self-regulation Theory 103
3.3.4 Spatial Distributions of Star Clusters 107
3.4 Summary and Discussion 111
4 Effects of Magnetic Fields on Gas Dynamics and Star Formation in Nuclear Rings 117
4.1 Overview 117
4.2 Numerical Methods 121
4.2.1 Governing Equations 122
4.2.2 Star Formation and Feedback 125
4.2.3 Magnetized Inflow Streams 125
4.2.4 Models 130
4.3 Evolution 130
4.3.1 Overall Evolution 131
4.3.2 Star Formation History 136
4.3.3 Magnetically Driven Accretion Flow 137
4.4 Magnetic Fields in the Ring 141
4.4.1 Growth of Magnetic Fields 141
4.4.2 Effects of Magnetic Fields on Star Formation 145
4.4.3 Vertical Dynamical Equilibrium 149
4.5 Summary and Discussion 150
4.5.1 Summary 150
4.5.2 Discussion 152
5 Conclusions and Future Work 157
5.1 Conclusions 157
5.2 Future Work 160
Bibliography 163
Appendix 178
A Orbit Integration of Sink Particles with the Coriolis Force 179
B Seed Magnetic Fields 185
C Magnetic Energy Conservation 187
D Mass Accretion Rates due to Maxwell and Reynolds Stresses 189
μμ½ 191λ°