1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-1 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-2 Sterrenstelsels en Cosmologie Docent: M. Franx, kamer 425 College assistent: Marcel van Daalen, kamer 438 Two books are relevant for this course. None are obligatory: Binney and Tremaine: Galactic Dynamics (B&T) (2nd edition) (40 dollars amazon, 30 dollars on kindle) Dates of the courses Usually on Monday, 11:15-13:00, but also on Thursdays 13:45-15:30 Feb 11,18,21,25, Mar 4,11,18,21,25, Apr 8,15, May 6,13,22 Always room room 106 Huygens Lab. Introduction into theory of galaxy dynamics, i.e. potential theory, orbits, distribution functions, equilibria, disks, mergers, etc. Extragalactic Astronomy and Cosmology Peter Schneider 79 euro bij bol, $70 bij kindle (50 euro equivalent) These books are not obligatory. Their level is very high (advanced Master course), but this means they remain useful throughout your career. 1 other book is also sometimes used: Binney and Merrifield: Galactic Astronomy (indicated with BM ) Het cijfer voor het college wordt voor 66% bepaald door het tentamen, en voor 33% door de ingeleverde huiswerk opgaven. Die moeten bij het begin van het volgende college worden ingeleverd. Een minimum cijfer van een 6 voor de huiswerk opgaves is nodig om deel te kunnen nemen aan het tentamen. Te laat inleveren van de huiswerk opgaven betekent het cijfer 0.
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-3 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-4 Brief content of the course 1) Introduction What is a galaxy? Classifications Photometry, exponentials, r1/4 profiles, luminosity function 2) Keeping a galaxy together: Gravity Potentials 3) Galactic Dynamics Equilibrium collisions, Virial Theorem Universe expansion Growth of galaxies by gravity Galaxy scaling relations 9) Galaxy formation - forming the stars Gas cooling and star formation formation of disks dynamical friction and mergers tidal tails in mergers 10) Observing galaxy formation High redshift galaxies from HST Fair samples of galaxies at high redshift 4) Galactic Dynamics continued Timescales Orbits 5) Collisionless Boltzmann Equation equilibrium, phase mixing derivation of distribution function 6) Velocity Moments Jeans equations comparison to observations 7) Mass distribution and dark matter Evidence for dark matter from rotation curves Solar neighborhood, Oort limit Elliptical galaxies and hot gas Clusters of galaxies, the universe Candidate dark matter particles 8) Galaxy formation
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-5 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-6 1. General Introduction Content Handout 1: i) What is a galaxy? Optical Radio X-Ray Dark Matter (halo) ii) Why do we study galaxies? iii) Optical Photometry iv) Luminosity Function v) Selection Effects Read from B&M: 4.1, (4.1.2), 4.1.3 to page 165, (4.1.4) 4.2, (4.2.2), not 4.2.3 4.3, to page 187 4.4, (not 4.4.2), 4.4.3 to page 217 4.6, to page 244 (4.6.2) subsection in brackets means for reading only i) What is a galaxy? Galaxies emit in many wavelengths [See the multiwavelength color show! (separate handout, also on website)] Radio: Continuum emission follows spiral arms Active nuclei produce jets, radio lobes... Line emission: HI 21 cm, CO, molecular lines Infrared: Continuum emission by dust Star forming regions, active nuclei Near Infrared: Red super giants, some extinction Optical-UV: Visible stars, dust absorbtion Emission lines Blue active nuclei X-Ray: (Double) stars, neutron stars, star forming regions Very hot gas
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-7 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-8 Active Nuclei produce emission at all wavelengths at all lengthscales: from very close to the nucleus ( pc) to the largest scale (> 10 kpc) Conclusion a Galaxy consists of several components: stars bulge red, old (?) r 1/4 law disk blue or red spiral arms, rings, bars exponential profile gas H I gas H 2 gas dust Hot Gas active nucleus black hole Dark Halo
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-9 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-10 Why study galaxies? What are the main questions? Optical images of galaxies and classification See the color handout for nice pictures! What is the structure of galaxies? What is their equilibrium? What are they made off? What is their mass distribution? All classification systems are idealizations. Independent of true size of the galaxy! Often used systems: How do they evolve in time? 1. Hubble-Sandage 2. de Vaucouleurs or How have they formed? Numerical types T (based on 2.) often used Disadvantages of ALL classifications Only based on optical image > independent of true size! Galaxies vary in more than one dimension Many galaxies are peculiar, i.e. inclassifiable
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-11 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-12
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-13 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-14
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-15 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-16
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-17 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-18 Homework Questions: 1) Describe in your own words 3 criteria which are used to classify spirals into Sa, Sb to Sd. 2) What is the type of the Milky Way? 3) Why do we classify the Magellanic CLouds not as ellipticals? They don t have spiral arms. 4) What is the type of the galaxy on the cover of BM? Give the reasons for your classification 5) How do you recognize mergers?
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-19 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-20 Quantitative photometry of galaxies First: photographic plates: Limited dynamic range Now: CCDs (= very sensitive TV camera s) Sizes 2048x2048 pixels Quantum efficiency 90 % Very good dynamic range Photometry > Imaging galaxies and measuring their brightness distribution Usually NOT resolved in stars Measure average surface brightness profile Ellipticals: King profile de Vaucouleurs law (r 1/4 ) Spirals: Disks: exponential profile Bulges: r 1/4 For elliptical galaxies we often find the r 1/4 law: I(R) = I e exp( 7.67[(R/R e ) 1/4 1]) where R e is the half light radius: half the light is emitted inside R e. Because of uncertainties in the background subtraction, we never know the exact half light radius. The parameter I e is the surface brightness at R = R e. No galaxy follows the r 1/4 law exactly!
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-21 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-22 An exponential disk has I(R) = I 0 exp( R/R d ) where R d is the disk scalelength. Many galaxies are modelled well by fitting an r 1/4 law to the bulge and an exponential model to the disk.
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-23 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-24 Luminosity Function Determine for each galaxy the intrinsic luminosity from apparent luminosity and distance. Correct for bandpass, internal absorbtion and absorbtion by the Milky Way. The luminosity function is defined by Φ dm = number density of galaxies in magnitude range (M,M + dm) The distribution of luminosities is given by a Schechter function Φ(L) = (Φ 0/L ) (L/L ) α exp( L/L ) Typical values: Φ = (1.6 ± 0.3) 10 2 h 3 Mpc 3 MB = 19.7 ± 0.1 + 5 log h α = 1.07 ± 0.07 L B = (1.2 ± 0.1) h 2 10 10 L Sun where H 0 = h100km/s The number of galaxies with a luminosity larger than L is given by N(> L) = L Φ(L )dl = N 0 Γ(1 + α, L/L )
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-25 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-26 Total amount of light produced l tot = 0 Φ(L )L dl = Φ L Γ(2 + α) = Φ L for α = 1 Hence, huge numbers of low luminosity galaxies expected, but finite luminosity. Most of the luminosity comes from galaxies with L = L. A simple approximation is that the universe is filled with L galaxies with a density Φ
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-27 Catalogs of galaxies most catalogs based on optical surveys e.g.: Revised Shapley-Ames Catalog Sandage and Tammann Third Reference Catalogue of Bright Galaxies de Vaucouleurs et al Sloan Digital Sky Survey 1 million galaxies + spectra! 1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-28 Selection effects in optical catalogs Consider galaxy with certain luminosity If galaxy too small: misclassified as star if galaxy too big: surface brightess is too low > not detected! Very important were Palomar Sky Survey Plates, these have been used for systematische surveys UGC: northern galaxies ESO catalog: southern galaxies Lauberts, Lauberts en Valentijn
1-2-2013see http://www.strw.leidenuniv.nl/ franx/college/ mf-sts-2013-c01-29 Homework questions 6) Given a galaxy with an exponential profile I(R) = I 0 exp( R/R d ) a) what is the total emount of light emitted? (Express in terms of I 0 and R d.) (Hint: integrate the light emitted over radius from 0 to infinity) b) what is the half light radius? (i.e., the radius in which half the light is emitted) (Hint: use the integral from 6, now to Re instead of infinity) 7) How can we attempt to classify galaxies automatically (i.e., by computer)? 8) What is the luminosity function? 9) Given a Schechter Luminosity function, what is the luminosity at which half of the total luminosity density is emitted by galaxies brighter than that luminosity? Assume α = 1. 10) What is the luminosity of a typical galaxy in terms of solar luminosities? 11) How can the total number of galaxy be infinite (per Mpc 3 )? Would that produce an infinite amount of light? 12) Find the website of a catalogue with more than 100.000 galaxies (and NOT the Sloan Digital Sky Survey ).