Sep 09, Overview of the Milky Way Structure of the Milky Way Rotation in the plane Stellar populations

Transcription

1 Sep 09, 2015 Overview of the Milky Way Structure of the Milky Way Rotation in the plane Stellar populations PE#4: (pick up a copy; 1 page) Kinematics of stars in the Milky Way disk Matching datasets in TOPCAT HW#2 is due Monday 3 minute presentation on your galaxy (see assignments) Send me 1 or 2 PDF slides by noon Monday Arecibo observing Saturday night at 11:15 Reading: Chapter 3

2 For HW #3, Mon Sep 14 Object Presenter Messier 81 Gabriel NGC 3628 Samuel Arp 220 Zachary I Zwicky 18 JiSoo Messier 106 John NGC 5128 James Messier 90 Paola

3 Messier 81 The Galaxies NGC Arp 220 IZwicky18 apod.nasa.gov/apod/ap html apod.nasa.gov/apod/ap html

4 Messier 106 The Galaxies NGC 5128 apod.nasa.gov/apod/ap html Messier 90 apod.nasa.gov/apod/ap html

5 Observing with the Arecibo Telescope We will conduct observations from SSB 521/3 on a number of nights this semester. You are invited to come by to watch us observe; attendance is optional (but we will have to arrange in advance, since the building is locked). Scheduled observations Sat Sep 10:15 pm (more in mid October?) Arrive at 10:15-10:20 pm; pls try to be on time so I can let you in. If you arrive late, call to reach us.

6 Program: A2982 PI: Mike Jones (CU grad)

7 HW #1 Grades in this class will be based on a curve; you get points for completing assignments. Homework counts 40%. This homework was graded out of 30 points. Please type the answers or write legibly. Be complete, giving references where appropriate, and always explaining your logic. Definitions: These aren t for me, but for you. Before the first prelim, does the definition give you what you need? parallax: is a displacement or difference in the apparent position of an object viewed along two different lines of sights and is measured by the angle or semi-angle of inclination between those two lines. This isn t really what we mean in astronomy-speak.

8 Puerto Rico is at latitude 18.3 deg North 18 Arecibo

9 With a little arithmetic, you can show that Redshift z = = obs rest rest = For cz ~ 3490 km/s, z ~ f rest f obs 1 f obs = f rest 1+z = = MHz

10 Some questions: How many WAPPs are there? How different would signals look with ON+OFF source in the separate polarizations? How much in advance do you know when you are observing? From notes, at rate A 10, about atoms : what is A 10? Why is this larger than anticipated? In WAPP search mode, how do you deal with a signal found in the overlapping (between boards) frequency range? How do astronomers determine the velocity of a galaxy without knowing its distance? How do you determine the distances of galaxies (other than Hubble s Law)? Won t absorption by dust change the perceived emission spectrum? How is this accounted for?

11 The Milky Way viewed edge-on

12 The Structure of the Milky Way Stars: Thin disk Thick disk (older, less massive) Bulge and/or bar Gas: Atomic (HI) In diffuse clouds More extended than stars Molecular (H 2 ) In dense clouds Follow stars, spiral arms Ionized (HII) Low mass, low density, large volume Dust: Mostly in spiral arms & molecular clouds

13 The Milky Way Stars contribute ~80% of the visible mass 80% in disk 20% in bulge Gas contributes ~20% of the visible mass Atomic gas (HI) ~ 2/3 of gas mass (H one) Molecular gas (H 2 ) ~ 1/3 of gas mass (molecular hydrogen Hot, ionized gas ( HII or H+) (H two) Dust Between stars Mostly in spiral arms and molecular clouds The gas and dust reside in the interstellar medium

14 Galactic Coordinates longitude & latitude l, b R,, z

15 Galactic Coordinates Differential rotation in the disk

16 Cartesian Galactic Coordinates Common use: centered on Sun Could also be centered on Galactic Center: beware of use! X, Y, X X points towards the Galactic Center Y points in the direction of the Sun s orbital motion Z is perpendicular to the disk U,V,W are the velocities in the directions X,Y,Z

17 Arecibo s view of the Galactic Plane The Arecibo telescope can steer within 20 deg of zenith; so -2.3 < Dec < 38.3

18 Arecibo s view of the Galactic Plane The Arecibo telescope can steer within 20 deg of zenith; so -2.3 < Dec < 38.3

19 The Milky Way as a Galaxy Advantages: nearby Lots of detailed data We can observe stars of all masses (esp. low mass) Supermassive (4 x 10 6 M ʘ ) black hole at center (SgrA*) Stellar streams: evidence for satellite disruption; disk warping Magellanic Stream: evidence for interaction with MCs Disk/bulge/halo separate (a) age; (b) kinematics; (c) metallicity. Disadvantages: Unremarkable as galaxies go SMBH is not active Benign environment Mature universe Optical wavelengths heavily extincted

20 The Milky Way components

21 2MASS View of the Milky Way What wavelengths correspond to J,H and K?

22 2MASS view of the MW Bulge 20% of Galaxy s light from the bulge, R~1 kpc. Stars: few Gyr old, metal-rich unlike the metal-poor stars of the halo; inner halo is also more round and does not show rotation Bulge rotates in prograde sense, like the Sun, but slower: <Vc> ~ 100 km/s A slight asymmetry of the bulge and additional kinematic data show that the Milky Way has a central bar extending to R=2-3 kpc. It is a Sbc galaxy or SABbc( r)

23 Milky Way Globular Clusters

24 B&T Milky Way Overview

25 Galactic Rotation l = 90 o l = 0 o Along any longitude, the observed radial velocity reaches a maximum at the tangent point, where R = R min.

26 Galactic Rotation Relations V obs = V(R) cos - V(R ) cos(90º-l ) = V(R) cos - V(R ) sin l At any longitude, V obs (d) depends on the rotation curve characteristics. Notice that we observe the max. V r from an object at the tangent point along any l.o.s. R min R ʘ = sin l

27 Galactic rotation

28 Differential rotation

29 The Local Standard of Rest Velocity of Sun: (10, 5, 7) km/s

30 Galactic rotation

31 Rotation in the disk

32 Galactic rotation Oort s constants A and B

33 Oort s Constants Local shear rate Local angular velocity Local vorticity Local slope of RC

34 Atomic H (HI) in the galaxy Also applies to molecular ISM clouds

35 Galactic Coordinates Q3 Q2 Q4 Q1

36 A bit of diversion with TOPCAT Demonstrate use of Joining files Join by position or other Can find matches or non-matches Demonstrate use of column statistics; you can select what statistics to display, not just default ones. Demonstrate making row subsets and then displaying/comparing them.