Galaxy Evolution Part 4 Jochen Liske Hamburger Sternwarte jochen.liske@uni-hamburg.de
Astronomical picture of the week NGC 1275 Central galaxy of the Perseus cluster Active Source: APOD
Astronomical picture of the week NGC 1275 Central galaxy of the Perseus cluster Active Source: APOD
Astronomical news of the week Most Earth-like planet with an atmosphere: GJ 1132b
Astronomical news of the week
1. Introduction 2. Overview of galaxies and physical processes 2.1 What is a galaxy? 2.1.1 Constituents 2.1.2 Structure 2.1.3 Main parameters 2.2 Basic elements of galaxy formation 2.2.1 Cosmology 2.2.2 Initial conditions 2.2.3 Structure formation 2.2.4 Gas cooling 2.2.5 Star formation 2.2.6 Feedback 2.2.7 Mergers 2.2.8 Dynamical evolution 2.2.9 Chemical evolution 2.3 Time scales 2.4 Some historical notes Contents
2.2 Basic elements of galaxy formation
2.2.1 Cosmology General relativity Cosmological principle (homogeneity and isotropy) FLRW metric Uniquely determined by geometry (k) and expansion history (R(t)) These are in turn determined by the mass-energy budget of the Universe:
2.2.2 Initial conditions The basic cosmological model does not explain the emergence of structure in the Universe. Source of initial density perturbations from which galactic structures could develop is still not entirely clear. Best bet: a period of inflationary expansion in the very early Universe (at end of GUT era) that inflates quantum fluctuations to a macroscopic scale
2.2.3 Structure formation Gravitational instability = amplification of initial density perturbations
2.2.3 Structure formation Increased density region Average density region Gravitational instability = amplification of initial density perturbations / 1 Collapse = decoupling from Hubble expansion t
2.2.3 Structure formation Increased density region Average density region Gravitational instability = amplification of initial density perturbations / 1 Collapse = decoupling from Hubble expansion DM relaxes halo Shocked gas t
2.2.4 Gas cooling Increased density region Average density region Gravitational instability = amplification of initial density perturbations Gas cooling depends strongly on: Temperature Density Chemical composition of gas Cooling segregation of gas from DM, collects as cold gas in centre of DM halo proto-galaxy (disk) / 1 Collapse = decoupling from Hubble expansion DM relaxes halo Shocked gas Gas cools through brems and recombination radiation t
2.2.5 Star formation Increased density region Average density region Gravitational instability = amplification of initial density perturbations Eventually: self-gravity of gas dominates runaway collapse, fragmentation star formation (SF) Details still poorly understood Initial mass function (IMF)? Two SF modes: Quiescent Bursting / 1 Collapse = decoupling from Hubble expansion DM relaxes halo Shocked gas Gas cools through brems and recombination radiation Star formation t
2.2.6 Feedback Increased density region Average density region Gravitational instability = amplification of initial density perturbations To prevent all of the gas from forming stars, the gas needs to be stopped from cooling, reheated or expelled. Feedback from: AGN (high-mass) Supernovae (low-mass) / 1 Collapse = decoupling from Hubble expansion DM relaxes halo Shocked gas Gas cools through brems and recombination radiation Star formation Feedback t
2.2.6 Feedback Increased density region Average density region Gravitational instability = amplification of initial density perturbations / 1 Collapse = decoupling from Hubble expansion DM relaxes halo Shocked gas Gas cools through brems and recombination radiation Star formation Feedback t
2.2.6 Feedback Increased density region Average density region Gravitational instability = amplification of initial density perturbations To prevent all of the gas from forming stars, the gas needs to be stopped from cooling, reheated or expelled. Feedback from: AGN (high-mass) Supernovae (low-mass) / 1 Collapse = decoupling from Hubble expansion DM relaxes halo Shocked gas Gas cools through brems and recombination radiation Star formation Details poorly understood t Feedback
2.2.6 Feedback Increased density region Average density region Gravitational instability = amplification of initial density perturbations / 1 Collapse = decoupling from Hubble expansion DM relaxes halo Shocked gas Gas cools through brems and recombination radiation Star formation Feedback t
2.2.6 Feedback Increased density region Average density region Gravitational instability = amplification of initial density perturbations / 1 Collapse = decoupling from Hubble expansion DM relaxes halo Shocked gas Gas cools through brems and recombination radiation Star formation Feedback t
2.2.7 Mergers Increased density region Average density region t Gravitational instability = amplification of initial density perturbations / 1 Collapse = decoupling from Hubble expansion DM relaxes halo Shocked gas Gas cools through brems and recombination radiation Star formation t Hierarchical growth Feedback
2.2.7 Mergers
2.2.7 Mergers
2.2.8 Dynamical evolution Tidal stripping Tidal interactions with other galaxies can remove stars, gas and DM, and perturb the structure:
2.2.8 Dynamical evolution Tidal stripping Ram-pressure stripping Movement of a satellite galaxy through the hot halo gas of another galaxy causes a drag to be exerted on the ISM of the satellite ablation of gas and dust:
2.2.8 Dynamical evolution Tidal stripping Ram-pressure stripping Internal dynamical effects ( secular evolution ) Changes of structure and morphology due to large-scale redistributions of mass and angular momentum Especially in galaxy disks (disk instability) Bars Pseudo-bulges
2.2.9 Chemical evolution Stars produce heavy elements through nuclear fusion. These are returned to the ISM by stellar winds or supernovae. The metallicity of the ISM and of newly formed stars changes over time. Changes the luminosities and colours of newly formed stars. Changes the cooling efficiency of the gas. Changes the abundance of dust. Evolution is made more complicated by: Infall of fresh gas Blow-out of gas by feedback processes Mergers
2.2 Basic elements of galaxy formation
Structure formation: DM only
Structure formation: DM only
Galaxy formation: numerical models Simultaneous simulation of DM and gas hydrodynamics + recipes for sub-grid physics : cooling, photo-ionisation, star formation and evolution, feedback
1. Introduction 2. Overview of galaxies and physical processes 2.1 What is a galaxy? 2.1.1 Constituents 2.1.2 Structure 2.1.3 Main parameters 2.2 Basic elements of galaxy formation 2.2.1 Cosmology 2.2.2 Initial conditions 2.2.3 Structure formation 2.2.4 Gas cooling 2.2.5 Star formation 2.2.6 Feedback 2.2.7 Mergers 2.2.8 Dynamical evolution 2.2.9 Chemical evolution 2.3 Time scales 2.4 Some historical notes Contents
2.3 Time scales Hubble time Timescale of cosmological evolution: 1/H 0 Dynamical time Typical time to cross a dynamical system: t dyn = 2 t ff = Cooling time Time it would take to lose all energy at current energy loss rate 3π 16 G ഥρ Star-formation time Time it would take to convert all cold gas to stars at current starformation rate Chemical enrichment time Merging time Typical time between mergers with similar-mass object Dynamical friction time Typical time for a satellite orbiting in large halo to lose its orbital energy
2.3 Time scales Relative time scales of prcesses are important Examples: Cooling time vs dynamical time Star formation time vs dynamical time Chemical enrichment time vs star-formation time No single time scale for galaxy formation itself!
1. Introduction 2. Overview of galaxies and physical processes 2.1 What is a galaxy? 2.1.1 Constituents 2.1.2 Structure 2.1.3 Main parameters 2.2 Basic elements of galaxy formation 2.2.1 Cosmology 2.2.2 Initial conditions 2.2.3 Structure formation 2.2.4 Gas cooling 2.2.5 Star formation 2.2.6 Feedback 2.2.7 Mergers 2.2.8 Dynamical evolution 2.2.9 Chemical evolution 2.3 Time scales 2.4 Some historical notes Contents
2.4 Some historical notes Before 1920s: nature of galaxies entirely unclear All within the Milky Way? Some island universes? 1755: Kant speculates about Weltinseln 1771 1784: Charles Messier lists 103 (later amended to 110) objects in his Catalogue of Nebulae and Star Clusters
Messier objects
2.4 Some historical notes Before 1920s: nature of galaxies entirely unclear All within the Milky Way? Some island universes? 1755: Kant speculates about Weltinseln 1771 1784: Charles Messier lists 103 (later amended to 110) objects in his Catalogue of Nebulae and Star Clusters Examples of data : drawings by Lord Rosse as seen through his 72 telescope in 1845:
2.4 Some historical notes Before 1920s: nature of galaxies entirely unclear All within the Milky Way? Some island universes? 1755: Kant speculates about Weltinseln 1771 1784: Charles Messier lists 103 (later amended to 110) objects in his Catalogue of Nebulae and Star Clusters 1864: Herschel s General Catalogue of Galaxies (5079 objects) 1888: Dreyer s New General Catalogue of Nebulae and Clusters of Stars, later supplemented by Index Catalogues (> 15,000 objects)
Andromeda (M31) around 1890
2.4 Some historical notes Before 1920s: nature of galaxies entirely unclear All within the Milky Way? Some island universes? 1755: Kant speculates about Weltinseln 1771 1784: Charles Messier lists 103 (later amended to 110) objects in his Catalogue of Nebulae and Star Clusters 1864: Herschel s General Catalogue of Galaxies (5079 objects) 1888: Dreyer s New General Catalogue of Nebulae and Clusters of Stars, later supplemented by Index Catalogues (> 15,000 objects) 1920: The Great Debate Harlow Shapley Heber Curtis
2.4 Some historical notes Before 1920s: nature of galaxies entirely unclear All within the Milky Way? Some island universes? 1755: Kant speculates about Weltinseln 1771 1784: Charles Messier lists 103 (later amended to 110) objects in his Catalogue of Nebulae and Star Clusters 1864: Herschel s General Catalogue of Galaxies (5079 objects) 1888: Dreyer s New General Catalogue of Nebulae and Clusters of Stars, later supplemented by Index Catalogues (> 15,000 objects) 1920: The Great Debate 1925: argument resolved by Hubble s observations of Cepheids in Andromeda Edwin Hubble
Distance measurements Cepheids = periodic variable stars with an empirical relationship between their period and luminosity (Henrietta Swan Leavitt, 1908) L P n, n 1.1... 1.2 Standard candle
2.4 Some historical notes Before 1920s: nature of galaxies entirely unclear All within the Milky Way? Some island universes? 1755: Kant speculates about Weltinseln 1771 1784: Charles Messier lists 103 (later amended to 110) objects in his Catalogue of Nebulae and Star Clusters 1864: Herschel s General Catalogue of Galaxies (5079 objects) 1888: Dreyer s New General Catalogue of Nebulae and Clusters of Stars, later supplemented by Index Catalogues (> 15,000 objects) 1920: The Great Debate 1925: argument resolved by Hubble s observations of Cepheids in Andromeda distance = 900,000 ly, far outside of MW (correct value: 2.5 x 10 6 ly) birth of extragalactic astronomy
2.4 Some historical notes 1912: Vesto Slipher discovers the systematic redshift of the spectra of spiral nebulae 1929: Edwin Hubble combines Slipher s redshifts with his own distance measurements:
2.4 Some historical notes Fundamental observation: linear relationship between distance and recession velocity: v = H 0 d (Hubble s Law) Successfully interpreted in the context of Einstein s General Relativity (1915) as the expansion of the Universe Birth of modern cosmology