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Models of chemical enrichment. Appears like the Dawn Fair as the Moon Bright as the Sun Majestic as the Stars by Nari Jeong 2007. 4. 9. 연령 , 금속 함량과 운동 상태에 의하여 은하계 내의 종족들을 구분 -> 금속 함량과 연령과의 관계가 중요 별의 금속 함량 : 별이 생겨난 모체인 기체에서 중금속의 농도화 ( enrichment ) 의 정도를 표시하는 것
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Models of chemical enrichment Appears like the Dawn Fair as the Moon Bright as the Sun Majestic as the Stars by Nari Jeong 2007. 4. 9
연령, 금속 함량과 운동 상태에 의하여 은하계 내의 종족들을 구분 -> 금속 함량과 연령과의 관계가 중요 • 별의 금속 함량: 별이 생겨난 모체인 기체에서 중금속의 농도화(enrichment) 의 정도를 표시하는 것 • 금속 함량이 풍부하다는 것은 상대적인 표현!! • 왜 중요한가? -> 은하 진화 과정에서는 화학과 역학이 서로 연결 되어 있기 때문 <관측> : 금속 함량비가 낮을수록 -> 은하원반으로부터 높은 곳 위치 • 성간 매질의 재순환(recycling) 기본 개념에 의해 생각!! < help thinking ^-^> 1. 성간 매질의 구름에서 별들 탄생 = 모체인 기체 함량 비 반영 2. 궤도 운동도 역시!! 3. 은하가 늙어 감에 따라 중 원소 함량 비 증가
Model of chemical enrichment • Interpretation of both observations of external galaxies and of stars within the Milky Way • First model : completely isolated system • Second model : vents metal rich gas • Third model : accretes metal-free gas from its surroundings <References> • Pagel, B.E.J., 1997. Nucleosynthesis and Chemical Evolution of Galaxies (Cambridge: Cambridge University Press) • Talbot, R.J & Arnett, W.D. 1971, ApJ 170, 409. Closed-box model
The closed-box model • Talbot & Arnett(1971) : chemical evolution of a portion of a galaxy such as the solar neighborhood. • Focuses on -> a narrow annulus of galactocentric radius <8.2.6 : Metallicities of disk galaxies p516 > The metallicities of the ISM of a disk galaxy -> strenghths of emission lines in the spectra of HII regions. -> depends systematically on : galactocentric radius • Assumes -> no material either enter or leaves this region. Turbulent motions -> keep the gas well stirred -> homogeneous Gas gradually consumed -> remain : heavy elements. • Metallicity Interstellar gas Z = Mh/Mg • Total mass -> forming a mass of new stars • instantaneous recycling approximation
The leaky-box model • Milky Way stars form in molecular cloud complexes ->no means closed boxes molecular -> small fraction -> turned into stars Supernovae!! -> out of the cloud : formation of globular cluster elliptical galaxies • Hartwick(1976) leaky-box model -> Milky Way’s halo p688 F10.39 • Line-strengths of elliptical galaxies : central velocity dispersions • Leaky-box model -> gas was exhausted. <Figure 5.18> • Contain both cool and hot parcels of gas -> ISM will consist of two phases one hot & one cold. • One-dimensional velocity dispersion -> corresponds temperature T
Hot component of the ISM : 200kms^-1 Dwarf : 10kms^-1 - little self-enrichment Giant elliptical : >200kms^-1 - self-enrichment • Gravitational potential -> gas is lifted f : a number of order a few Esn : energy injected into the ISM per unit mass converted into stars C : increse from a value smaller than unity for giant elliptical galaxies to one of order a few for dwarf ellipticals • -> Supernovae : lift gas from the galaxies • Unfortunately!! -> uncertain Why? Dark halos