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Astro 3303 “Galaxies across Cosmic Time”

A “core” course in the Astronomy major with a general astronomy concentration

Prereqs: Some background in physics and math. Some astronomy

helps; otherwise get hold of any intro astro textbook and read Appendices A & B in the textbook.

Textbook: “Extragalactic Astronomy and Cosmology” by Peter

Schneider

http://www.astro.cornell.edu/academics/courses/astro3303/

Emphasizing current and future observations/facilities/programs

http://www.astro.cornell.edu/academics/courses/astro3303

Fall 2015 Astro 3303

http://www.astro.cornell.edu/academics/courses/astro3303

• Required work:

• 10 homework assignments

• 2 in-class tests (30 min each) on M Oct 05 and M Nov 16 (no makeups except in cases of emergency/illness)

• 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; “you had to be there…”)

• 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 handout (2 pages)

http://www.astro.cornell.edu/academics/courses/astro3303

I am *not* Dominik Dominik is a distinguished young faculty member at Cornell. He will introduce himself further when he starts lecturing in a few weeks.

A bit about me (Martha Haynes) • B.A., Wellesley College • M.S. and Ph.D. Indiana University • 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), CSIRO (Australia),ASTRON(Neth)

• Vice-President, International Astronomical Union • Vice-Chair, National Research Council’s 2010 Astronomy & Astrophysics

Decade Survey • OSTP designee to Astronomy & Astrophysics Advisory Cmte

A bit about me

ALFALFA: The Arecibo Legacy Fast ALFA Survey

Me with ALFA: The Arecibo L-band Feed Array… a 7 pixel “radio camera”

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.

CCAT: 25 meter submm telescope

Me, at 18,400 feet in the high Atacama desert in Chile, at the site of the future CCAT (submillimeter wavelength telescope)

CCAT Site on C. Chajnantor

HW #1 due Wed Sep 2nd

Basic plan: • Homeworks are designed to help you learn and apply the

material covered in class.

• At times, they will require you to use astronomical software/tools/databases (e.g. this week’s)

• At times, they will include in-class presentations and preparations for your final project.

• Your graded homeworks should be included in your portfolio, along with a print out the homework assignment.

• If possible, type your answers; if not, please write legibly and be sure to explain your reasoning, show your calculations and cite your references.

Astro 3303 • For next Mon, read Chapter 1 in textbook • Bring your portfolio, including PE #1

• For Wed Sep 2, do homework #1

TOPCAT: http://www.star.bris.ac.uk/~mbt/topcat/ SDSS: http://www.sdss.org NASA Extragalactic Database (NED): http://ned.ipac.caltech.edu Ned Wright’s CosmoCalc: http://www.astro.ucla.edu/~wright/CosmoCalc.html

Software/database/archive tools we will access and use:

HW #1 due Wed Sep 2nd

Part I: Observing galaxies with the Arecibo Telescope Part II: Install and learn to use TOPCAT Part III: Definitions, units etc.

Record enough for your own understanding (this isn’t for us, but it will be useful for you).

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 Sept 5 @ 10:45 pm Sat Sep 12 @ 10:15 pm (more in mid October?)

• More info next week.

Try to download and install it; if you have problems check with me!

TOPCAT

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, we 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

Portfolio exercise: the first entry

Today’s entry includes some important numbers, many of which you may be familiar with. It also includes some useful definitions and concepts which we will review in the coming weeks.

Be sure to bring this handout (and your portfolio) with you next Monday; we will add to it regularly and you’ll need it to refer back to.

Review any concepts you are not familiar with, especially units of distance, magnitudes, solar units, etc.

During other classes, we will discuss issues/topics centered on the PE’s.

History - and Fate - of the Universe Hot Big Bang Model

13.8 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?

When did the clusters of galaxies form? How do clusters evolve?

What is the impact of environment on galaxy evolution?

Hubble’s Law The dominant motion in the Universe is the smooth expansion

known as the “Hubble flow”. Hubble’s Law: Vobs= HoD

where Ho is Hubble’s “constant” and D is distance in Mpc

= 1+v/c

1-v/c – 1 Recessional

velocity =

Spread in velocity for objects in a cluster due to their orbital

motion within the cluster.

Hubble’s constant X Distance

Hubble’s “constant” = 70 (?67.4?) km/s per Mpc

The Doppler Shift

• 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.

This reduces to the

simple Doppler formula

(above) for v << c.

Simple Doppler formula

Relativisitic Doppler formula

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 - = 0.995 c In fact, the Cosmic Microwave Background photons have a redshift z = 1000! (Stay tuned…..)

1

11 ( ) 2

time

• Do hierarchical models predict this behavior?

• Can they give us any insight into what is going on?

• How did the structures we see today form and evolve?

Hierarchical models

Ω = The ratio of the average density of the universe to the critical density

tot = rad + bary + DM +

Astronomy Picture of the Day: Aug 25, 2013 http://www.apod.nasa.gov/apod/

The Colliding Spiral Galaxies of Arp 271 Credit & Copyright: Gemini Observatory, GMOS-South, NSF

What about this image is interesting? What questions do you want to know the answers to?

Astronomy Picture of the Day: Aug 25, 2013 http://www.apod.nasa.gov/apod/

What about this image is interesting? What questions do you want to know the answers to?

Messier 31: a spiral galaxy

The Milky Way looks fairly similar to M31

Messier 31: a spiral galaxy

If this were the Milky Way, here is where the Sun would be

Observing the night sky

Orion the consellation

This photo shows roughly what your eye can see.

http://apod.nasa.gov/apod/ap040304.html

Orion

The constellation superposed on a wide angle view.

http://apod.nasa.gov/apod/ap040304.html

Telescopes: let us see more detail, fainter objects

Orion constellation APOD 030207

Orion: the Constellation

Messier 42: The Orion Nebula

• Combined image made from originals obtained with Hubble and Spitzer

Orion: naked eye vs. telescope

Using a special filter

The Milky Way in the Night Sky http://apod.nasa.gov/apod/ap100823.html

A Milky Way Shadow at Loch Ard Gorge (Australia) Credit & Copyright: Alex Cherney Terrastro

The Milky Way in the Night Sky http://apod.nasa.gov/apod/ap091225.html

Graceful Arc Credit & Copyright: Tony Hallas

What does the night sky look like? The disk of

the Milky Way, our galaxy

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 (>109 K)

• Gives off thermal radiation (stars, dust) and non-thermal radiation (energetic sources like supernova remnants, black holes, etc)

• Can be from 106 solar masses to ~1012 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.

More concepts/numbers:

• A galaxy is a self-gravitating collection of about 106 to 1011 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 106 to 1012 M (1 solar mass

is 2 x 1030 kg), and sizes ~ 1-100 kpc (1 pc = 3.1 x 1016 m). Galaxies that rotate have Prot ~ 10-100 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.

Messier 31, The Andromeda Galaxy

A galaxy is a single, identifiable object containing billions (and billions) of stars, gas clouds, dust clouds and … dark matter!

Not all galaxies are the same! What is different about them?

http://mcdonaldobservatory.org/news/gallery/elliptical-galaxy-

ngc-4621

NGC 4622 http://apod.nasa.gov/apod/

ap020125.html

Not all spirals are the same!

What is different about them?

NGC 4622 http://apod.nasa.gov/apod/

ap020125.html

Messier 74 http://apod.nasa.gov/apod/

ap011004.html

A bit about galaxy names • Messier catalog

• Charles Messier 1771

Galaxy Names “Messier”: included in list of celestial objects by Charles Messier in

1771. He was looking for comets but found all these other interesting (but annoying to him) objects (star clusters, planetary nebulae, galaxies etc); 103 entries

“NGC”: included in New General Catalog of Nebulae and Clusters of

Stars, compiled by John Dreyer in 1888 as an update to John Herschel’s 1786 Catalog of Nebulae and Clusters of Stars;

7840 entries “IC”: included in the “Index Catalog”, a list of an additional 5286

galaxies, nebulae, and star clusters discovered between 1888 and 1907.

Andromeda, Phoenix, Leo I, Leo II, Leo P: names based on constellation

in which they are located (but have nothing to do with the stars in the constellation!)

J142657.3+243138: Modern discoveries, except very nearby objects,

are given names based on their coordinates. “AGC”: The “Arecibo General Catalog”, our private database

The Hubble “Tuning Fork” Diagram

Notice there is a difference in color as well as shape! What does that tell us about the stars in the galaxies?

Image from Galaxy Zoo

The Milky Way as a Galaxy

Diameter ~75,000 light yrs Sun-to-Center ~ 24,000 l.y. Thickness ~ 3,000 light yrs.

Blue coloring reveals the presence of young massive

stars

But: dust hides the blue light!

The Milky Way as a Galaxy

Property Value

Morphological type SBb *

Luminosity in stars 1010 solar luminosities

Mass in stars 5 x 1010 solar masses

Total mass (luminous+dark matter) 1012 solar masses

Diameter of stellar disk 25 kpc ~ 80,000 light years

Diameter of stellar halo 100 kpc ~ 325,000 light years

Diameter of dark matter halo More than 200 kpc

Period of Sun’s revolution around Galactic Center

200 million years

Galactic Components

• Halo: • Old stars, globular

clusters • Spherical • Random motions • Large radius!

• Bulge • Oldish stars • Spherical • Random motions • Small!

• Disk • Young stars, gas

clouds, HII regions • Thin (youngest)

/thick (older) disk • Circular rotation in

the disk plane • Intermediate size

Motions in the Milky Way

Spheroid components (bulge, halo) • random motions around the

Galactic Center • no preferred plane

Disk stars/clouds orbit differentially (as individuals) • circular motion in the disk • V(R

) ~ 220 km/s

The Sun orbits the center of the Milky Way once every 225 million years…

Motions in the Milky Way’s disk The Sun is located 8 kpc (25,000 light years) from the Galactic Center. The Sun orbits the Galactic Center in a circular orbit at a velocity of 220 km/s. The orbital period of the Sun around the Galactic Center is about 225 million years.

Stellar “Populations”

• Once a star forms, it retains its orbital characteristics, although the gas around it may collapse further toward the disk.

Age sequence Stage of Collapse -- different spatial distribution -- different orbital characteristics

-- different metallicities (abundance of heavy elements, like C, N, O, Fe, Al

• Halo & Bulge (older, “metal poor”)

• Disk (younger, more metals)

Collapse of the Proto Galaxy

1. Protogalactic gas clouds, roughly spherical; motions randomly oriented around center of mass

2. Collapse along axis of rotation => flattened disk

3. Disk rotation speeds up as it becomes flatter => conservation of angular momentum (same as skater who pulls arms in)