- PDF Free Download

Size: px

Start display at page:

Download ""

Theresa Williams
5 years ago
Views:

3 Astro 3303 Galaxies across Cosmic Time Prereqs: 1 intro course in astronomy, 1 intro course in physics and 1 semester calculus (i.e., the basics) Basic laws of radiation, the layout and interpretation of the H-R diagram, the evolution of the Sun and how it differs from that of high mass stars, basic nucleosynthesis, basic understanding of cosmic history, etc. If you don t meet this requirement formally, talk with me. Textbook: Extragalactic Astronomy and Cosmology by Peter Schneider

5 Spring 2012 Astro Required work: 10 homework assignments 2 in-class tests (30 min each) on T Feb 28 and R Apr 05 (no makeups) Final paper/project including an in-class presentation during last week of class (notice the advanced warning!) In class activities and exercises (no makeups for these) A portfolio in which you will keep all of your work done before the end of classes. You should plan on bringing this to class regularly. Pick up today s portfolio handouts (1 page)

6 B.A., Wellesley College M.S. and Ph.D. Indiana University A bit about me Postdoc, staff scientist, Arecibo Observatory (Puerto Rico), National Astronomy and Ionosphere Center Assistant director, Green Bank Observatory (West Virginia), National Radio Astronomy Observatory Cornell faculty since 1983 Interim president, Associated Universities, Inc (AUI not for profit NGO based in Washington DC, during sabbatic leave) Visiting scientist: Mt. Stromlo Observatory (Australia), European Southern Observatory (Germany), Obs. Astron.&Univ. Milano/Firenze/Bologna (Italy) Vice-President, International Astronomical Union Vice-Chair, National Research Council s 2010 Astronomy & Astrophysics Decade Survey OSTP designee to Astronomy & Astrophysics Advisory Cmte

a galaxy s evolution of its local intergalactic environment.

7 A bit about me My research uses many telescopes but especially Arecibo. I study observational cosmology, the structure of the universe and the impact on a galaxy s evolution of its local intergalactic environment. ALFALFA: The Arecibo Legacy Fast ALFA Survey Me with ALFA: The Arecibo L-band Feed Array a 7 pixel radio camera

8 Last week: UAT12

9 CCAT: 25 meter submm telescope CCAT Site on C. Chajnantor Me, at 18,400 feet in the high Atacama desert in Chile, at the site of the future CCAT (submillimeter wavelength telescope) ALMA 12m antenna Oct 11

12 We will look more at this in class on Thursday.

13 Astro 3303 For Thurs, read Chapter 1 in textbook Bring your portfolio, including PE #1 For next Tuesday, do homework #1 Software/database/archive tools we will access and use: TOPCAT: SAOImage:DS9 SDSS: at RA, Dec = 195.0, MAST: VAO:

14 Your Astro3303 portfolio Astronomers observe. The sky (and objects in the sky) change(s). Astronomers keep records of what they observe: their impressions, what happened, what they think. => We ll use the portfolio to develop your thinking and approach to interpreting images and datasets and to keep track of useful information. At the end of the semester, your portfolio should contain all of your assignments, including the homeworks and in-class activities. During many classes, I will hand out assignments which will be done, in large part, during class. If you are not in class, you cannot make up the assignment. Everyone is allowed to miss a reasonable number of classes for good reasons. But if you re not here, you miss out on the discussion and participation, so there is no way to make up the activity

15 Portfolio exercise: the first entry During class today, follow along and answer what you can. Then finish anything you don t get to in class at home. Be sure to bring it (and your portfolio) with you on Thursday. PE #1 Record important numbers and definitions for future reference.

16 History - and Fate - of the Universe Hot Big Bang Model billion years ago, the universe was much hotter and much denser than it is today. A tremendous release of energy took place: the Big Bang event. Since then, the universe has been expanding. Will the universe keep expanding? Or will the expansion halt? When did the galaxies form? How do galaxies evolve?

17 Hubble s Law The dominant motion in the Universe is the smooth expansion known as the Hubble flow. Hubble s Law: V obs = H o D where H o is Hubble s constant and D is distance in Mpc Spread in velocity for objects in a cluster due to their orbital motion within the cluster. Recessional velocity = = 1+v/c 1-v/c 1 Hubble s constant X Distance Hubble s constant = 70 km/s per Mpc

18 The Doppler Shift Simple Doppler formula This reduces to the simple Doppler formula (above) for v << c. Relativisitic Doppler formula Light emitted by a source moving towards us appears bluer. Light emitted by a source moving away from us appears redder. The amount of blueshift or redshift depends on source velocity.

19 Relativistic Doppler Formula We observed galaxies/quasars with redshifts of ~7-10 That does not mean that they are traveling faster than the speed of light This reduces to the simple Doppler formula for v << c. For z= 10, this becomes ( ) v = c 1 - = c In fact, the Cosmic Microwave Background photons have a redshift z = 1000! (Stay tuned: next week)

20 Hierarchical models How did the structures we see today form and evolve? Do hierarchical models predict this behavior? Can they give us any insight into what is going on? time

WMAP+BAO+SN parameter summary Description Symbol Value Age of universe t H 13.73 ± 0.12 Gyr Hubble constant H o 70.1 ± 1.

21 WMAP+BAO+SN parameter summary Description Symbol Value Age of universe t H ± 0.12 Gyr Hubble constant H o 70.1 ± 1.3 km/s/mpc Baryon density Ω b ± Dark matter density Ω dm ± Dark energy density Ω Λ ± Age at decoupling t cmb ,-3115 yr

23 Astronomical objects: galaxy What is a galaxy? Composed of billions of stars, gas clouds, dust clouds, diffuse gas, black holes, etc. Variable shape. Milky Way has disk, bulge, halo (why?) Individual objects have different temperatures from really cold (< 3K) to really hot (>10 9 K) Gives off thermal radiation (stars, dust) and non-thermal radiation (energetic sources like supernova remnants, black holes, etc) Can be from 10 6 solar masses to ~10 12 solar masses Individual components generate energy by different processes thermonuclear fusion (stars), collisions among particles, magnetic fields, etc. (i.e. many different mechanisms). Individual components visible at different wavelengths.

24 Definition: what is a galaxy? A galaxy is a self-gravitating collection of about 10 6 to stars, plus an amount up to ~same by mass of gas, and about 10X as much by mass of dark matter. The stars and gas are about 70% hydrogen by mass and 25% helium, the rest being heavier elements (called "metals"). Typical scales are: masses between 10 6 to M (1 solar mass is 2 x kg), and sizes ~ kpc (1 pc = 3.1 x m). Galaxies that rotate have P rot ~ Myr at about 100 km/s. The average separation of galaxies is about 1 Mpc. Between galaxies there is very diffuse hot gas, called the intergalactic medium (IGM); in clusters this is called the intracluster medium (ICM). It was much denser in the past before galaxies formed, accreted the gas and converted it into stars.

25 Morphological Classification

26 Galaxy Zoo

28 Galaxy Zoo

29 Galaxy Zoo

30 Galaxy Zoo What physical processes drive morphological differences? Do galaxies change their morphology as they evolve? Morphological segregation Ellipticals dominate in high density regions (clusters) Spirals dominate low density regions Mergers/.interactions/disturbed morphology more common at earlier epochs in the history of the universe.

31 The Sombrero Galaxy

32 IZw 18

33 Hoag s Object Ring galaxy

34 NGC 520: the Flying Fish

35 Arp 295

36 The Perseus Cluster

37 NGC 1275 (galaxy in a cluster of galaxies)

38 Abell 370

40 The Milky Way as a Galaxy Diameter ~25 kpc R ~ 8 kpc Thickness ~ 4 kpc

41 The Milky Way The Milky Way is known in a fair amount of detail, and both the gas and stars split cleanly into different populations or phases.

42 Constituents of the Milky Way The Milky Way is known in a fair amount of detail, and both the gas and stars split cleanly into different populations or phases. Stars: Disk: 6+ x M Bulge: ~ M Halo: ~10 9 M Globulars: ~10 8 M Gas: H 2 clouds: ~10 9 M HI gas: 5 x 10 9 M HII regions: ~10 8 M Dark matter: Halo: 5.5 x to 2 x M

43 The size of a galaxy Optical image Starlight

44 The size of a galaxy Radio image Atomic gas (HI) Optical image Starlight

45 Rotation curves: V(R) : variation of rotation speed with distance from center of galaxy V rad (R) : observed variation of radial velocity with distance from center

46 Portfolio Ex #1 Messier 31 The Andromeda nebula (galaxy) NGC 205 Consider the two small galaxies: M32 and NGC 205. M32

47 The Local Group of Galaxies Two main galaxies: Milky Way Andromeda (M31) Lots of dwarf galaxies Distance from MW to Andromeda: 2.5 Mlyr = 778 kpc Cartoon from E. Grebel

48 PE #1: Group discussion How would you determine whether or not M32 and NGC 205 were small satellites of M31 or rather more distant galaxies (in the background)? Be very specific about what you would measure and how that would lead you to the answer. M31 has an observed heliocentric radial velocity of -300 km/s. Explain that value in the context of Hubble s Law.

AST-1002 Section 0459 Review for Final Exam Please do not forget about doing the evaluation!

AST-1002 Section 0459 Review for Final Exam Please do not forget about doing the evaluation! Bring pencil #2 with eraser No use of calculator or any electronic device during the exam We provide the scantrons