1. GALAXIAS

2. Optico Infrarojo

5. The Galactic Disk The disk of our Galaxy is made up of three main components:  Stars  Gas  Dust

6. The gas in between stars is the “Interstellar Medium” (or “ISM”) Like everywhere, most gas in the disk is hydrogen. Molecular (H 2 ): Cold, dense, tightly clumped. Stars form within molecular clouds. “Neutral” or Atomic (HI): Cool, less dense, less tightly clumped. Most common phase; the reservoir for forming the next generation of stars. “Ionized” (HII): Hot, more diffuse. By-product of forming young stars.

7. Atomic HI Molecular H 2 Ionized HII Gas is compressed, and cools Young massive O-stars form, and ionize the gas Young massive stars die out, and electrons and nuclei recombine

8. Fountains and Blowouts SNe from newly formed massive stars can make holes in the disk, driving material out of the Galaxy or redistributing it

9. Blowout in M82 “starburst” galaxy… Red is “false color”, showing location of extremely hot gas detected in X-rays. Hot because the gas is mostly the “ejecta” from supernovae!

10. Los brazos de la galaxia son regiones de alta densidad donde ocurre la mayor parte del proceso de formación de nuevas estrellas. Por otro lado, las ondas de choque generadas por explosiones de estrellas evitan que los brazos se dispersen.

11. Los brazos no son rígidos; más bien son ciertas zonas que las estrellas atraviesan en su movimiento de rotación alrededor del centro galáctico. Se calcula que el Sol ya dio varias vueltas completas. En este momento, está en una zona "tranquila", al borde de un brazo secundario.

12. The Bulge: A Very Crowded Neighborhood The density of stars in the bulge is about 50,000 per cubic parsec By comparison, the nearest star to the Sun is 1.3 pc away!

13. Milky Way is believed to have a bar at its center…

14. The Galactic Halo: Ancient Stars No gas, so no star formation… …just a bunch of old stars, either by themselves or in globular clusters.

15. Stuff in Galaxies moves in two basic ways… Randomly –Highly elliptical orbits, plunging in and out of the center of the galaxy, at random orientations. Ordered Rotation –Nearly circular orbits (like planets around the Sun)

16. Side View of the Milky Way The “halo” is really the “stellar halo” – turns out there’s actually a larger halo we can’t even see! Globular clusters live in the halo

17. Turns out there’s a lot of this invisible matter.

18. Overall Properties of the Galactic Disk, Halo, and Bulge PropertyDiskHaloBulge Shapehighly flattened like a frisbee roughly spherical; mildly flattened M&M shaped Star Typesyoung and oldonly old starsyoung and old stars; more old stars at greater distances from center ISMgas and dustno gas or dustgas and dust, especially in inner regions New Stars?ongoing star formationno star formation for past 10 billion years ongoing star formation in inner regions Dynamicscontents move in circular orbits in the Galactic plane stars have random orbits in three dimensions largely random orbits with some net rotation about the center Substructurespiral armsno obvious substructurenucleus; ring of gas and dust near center; bar Coloroverall white color with blue spiral arms stars reddish in color due to old age and cool temperatures yellow-white due to mix of stars

19. Observational tracers of magnetic fields perpendicular field in 2 or 3 kpc Polarization of starlight: perpendicular field in 2 or 3 kpc orientation // B ⊥ ------------- 9000 stars parallel field, in situ (masers, clouds) Zeeman splitting : parallel field, in situ (masers, clouds) △ ∝ B // ------ 30 masers perpendicular field Polarization at infrared, mm: perpendicular field orientation // B ⊥ ------ clouds & star formation regions vertical field structures (added) Synchrotron radiation: vertical field structures (added) total intensity S ∝ B ⊥ 2/7, p% ∝ B ⊥ u 2 / B ⊥ t 2 parallel field, integrated (the halo & disk) Faraday rotation: parallel field, integrated (the halo & disk) RM ∝ ∫ n e B // ds ------ 500 pulsars + >1000 EGSes

20. Large-scale magnetic field in the Galactic disk The largest coherent field structrue detected in the Universe!

21. Poloidal & Toroidal fields near GC Toroidal fields (Novak et al. 2003, 2000) permeated in the central molecular zone central molecular zone (400pc*50pc) (400pc*50pc) sub-mm obs of p% toroidal field directions determined by averaged RMs of plumes or SNR! Poloidal field filaments Unique to GC --- dipolar geometry! (Morris 1994; Lang et al.1999) (from Novak et al. 2003) 150pc GC Predicted B-direction

22. The Milky Way is a “spiral” galaxy, sometimes also called a “late type” galaxy. The Milky Way: A Barred Spiral Galaxy

23. Side View “edge-on” Top View “face-on”

24. “Sombrero Galaxy”

25. Elliptical GalaxiesElliptical Galaxies (or just “ellipticals”) –No disk –No disk! old! “spheroidals”

26. “S0” galaxies: Like ellipticals, but usually a bit flatter.

27. Ellipticals Lenticulars Unbarred and Barred Spirals Early TypesLate Types

28. Varying amounts of bulge & disk components suggests different formation & evolution history Older Stars Gas Poor More Massive On-going Star Formation Gas Rich Less Massive On average…

29. Early-Type Galaxies from the Sloan Digital Sky Survey (SDSS)

30. (red because of dust) Late-Type Galaxies From SDSS

31. ??? “Dwarf” or “Irregular” Galaxies There are galaxies beyond the Hubble Sequence that continue this trend.

32. Low mass (10 7 -10 9 stars, vs 10 10 for spirals) High star formation rates (usually) No obvious bulge or spiral patterns. Most numerous type of galaxy in the Universe! DwarfIrregular “Dwarf” or “Irregular” galaxies tend to have more chaotic appearances…

33. Dwarf galaxies from the Sloan Digital Sky Survey.

34. “Gas Infall” Galaxies continue to form stars. –Just enough gas in galaxy disks today to form stars for <10 9 years. –Fresh gas must keep it going. Fraction of metals (non-H, He) in stars is lower than expected. –Fresh Hydrogen must be flowing in.

35. Gravity pulls galaxies together! They can orbit each other & eventually merge! “Merging” or “Galaxy Interactions”

36. “The Antennae” (Hubble Image @ Right)

37. Multiple cores in some ellipticals in clusters of galaxies

38. “Minor Mergers” We know this is currently happening…

39. Jupiter M16 (Eagle) M17 (Horseshoe) M8 (Lagoon) Milky Way Hale-Bopp Zoom-in Picture credit: W. Keel

40. Eagle Nebula (M16)

41. Eagle Nebula (M16)

42. Eagle Nebula (M16)

43. Eagle Nebula (M16) size of our solar system