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

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

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

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

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

Spring 2012 Astro 3303

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

• 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)

A bit about me • 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)

• 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.

Last week: UAT12

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)

ALMA 12m antenna Oct ‘11

CCAT Site on C. Chajnantor

We will look more at this in class on Thursday.

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

• For next Tuesday, do homework #1

TOPCAT: http://www.star.bris.ac.uk/~mbt/topcat/ SAOImage:DS9 http://hea-www.harvard.edu/RD/ds9/ SDSS: http://skyserver.sdss3.org/dr8/en/ at RA, Dec = 195.0, 28.02 http://cas.sdss.org/astro/en/tools/chart/navi.asp?ra=210.9158&dec=%2029.91444&opt=glsi

MAST: http://archive.stsci.edu/index.html VAO: http://www.usvao.org/

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

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

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.

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

13.69 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?

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 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: next week)

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

WMAP+BAO+SN parameter summary Description Symbol Value

Age of universe tH 13.73 ± 0.12 Gyr

Hubble constant Ho 70.1 ± 1.3 km/s/Mpc

Baryon density Ωb 0.0462 ± 0.0015

Dark matter density Ωdm 0.233 ± 0.013

Dark energy density ΩΛ 0.721 ± 0.015

Age at decoupling tcmb 375938 +3148,-3115 yr

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.

Definition: what is a galaxy?

• 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.

Morphological Classification

Galaxy Zoo http://www.galaxyzoo.org/

Galaxy Zoo http://www.galaxyzoo.org/

Galaxy Zoo http://www.galaxyzoo.org/

Galaxy Zoo http://www.galaxyzoo.org/

• 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.

The Sombrero Galaxy

IZw 18

Hoag’s Object “Ring galaxy”

NGC 520: the “Flying Fish”

Arp 295

The Perseus Cluster

NGC 1275 (galaxy in a cluster of galaxies)

Abell 370

The Milky Way as a Galaxy

Diameter ~25 kpc R ~ 8 kpc

Thickness ~ 4 kpc

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.

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 1010 M

Bulge: ~ 1010 M

Halo: ~109 M

Globulars: ~108 M

Gas: H2 clouds: ~109 M

HI gas: 5 x 109 M

HII regions: ~108 M

Dark matter: Halo: 5.5 x 1012 to

2 x 1012 M

The size of a galaxy…

Optical image Starlight

The size of a galaxy

Radio image Atomic gas (HI)

Optical image Starlight

Rotation curves: • V(R) : variation of

rotation speed with distance from center of galaxy

• Vrad (R) : observed variation of radial velocity with distance from center

Portfolio Ex #1

Messier 31 The

Andromeda nebula

(galaxy)

Consider the two small galaxies: M32 and NGC 205.

M32

NGC 205

The Local Group of Galaxies

Cartoon from E. Grebel

Two main galaxies:

• Milky Way

• Andromeda (M31)

Lots of dwarf galaxies

Distance from MW to Andromeda:

2.5 Mlyr = 778 kpc

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.