Formation and Evolution

Galaxies:Formation and Evolution : 

Galaxies:Formation and Evolution

What are galaxies? How did they form? : 

What are galaxies? How did they form? A look at nearby galaxies The cosmic “time machine” The Big Bang; expansion of the universe New techniques allow a remarkably detailed look at galaxies as they were billions of years ago. Galaxies have changed over the history of the universe. Fossil evidence from the Milky Way and nearby galaxies. The first stars and the formation of galaxies.

Galaxies Today : 

Galaxies Today Spiral, elliptical, irregular Stellar and gas content linked to morphology Dwarf galaxies most common Dark matter dominates overall dynamics Disk and bulge components; differ in motions and stellar properties

The Cosmic Time Machine : 

The Cosmic Time Machine Astronomical telescopes can’t help viewing the past. Distance and time are always mixed in astronomical observations. The finite speed of light means that we always see things after they have happened–a delay of 8 minutes for the Sun and about 12 billion years for the most distant galaxies we can observe. In other words,

Expansion of the Universe : 

Expansion of the Universe Features in the spectra of galaxies are essentially always observed at wavelengths longer than the corresponding features in laboratories on Earth (the “redshift”). The cosmological redshift is not exactly a Doppler shift, but is linked to the expansion of space as light propagates as well as the gravitational field of the universe. Hubble found a redshift-distance relation that could be interpreted as a uniform expansion. Friedmann had shown that such an expansion was a solution to Einstein’s equations.

Slide 15: 

Lookback time Observable quantity is redshift z Need distance scale and cosmology to derive lookback time to a given redshift Distance has multiple definitions in an expanding Universe

Slide 16: 

z = shift/initial wavelength

Slide 17: 

Redshift versus lookback time WMAP cosmology: Hubble constant 71 km/s/Mpc Flat spacetime W(matter)=0.27

Galaxy evolution : 

Galaxy evolution Episodic: starburst, interactions, mergers Passive: aging of elliptical galaxies Changes in spiral:elliptical mix (Butcher-Oemler effect)

Slide 21: 

Here and now: Coma E/S0 members

Slide 22: 

Then: spirals in Abell 851 (HST)

Gas in clusters of galaxies can sweep a spiral clean : 

Gas in clusters of galaxies can sweep a spiral clean But that’s a whole different PowerPoint…

Hubble Space Telescope : 

Hubble Space Telescope 2.4m optics, now diffraction limited Detectors from 0.11-2 microns Lifetime 1990-2007? Upgrades/repairs in the past via shuttle servicing (not without risk)

Chandra X-Ray Observatory : 

Chandra X-Ray Observatory Imaging optics, 0.5-arcsecond resolution High energy resolution for imaging data Very powerful probe of accretion history (that is, quasars and black-hole growth) Complemented by ESA’s XMM-Newton

8-10 meter optical/IR telescopes : 

8-10 meter optical/IR telescopes 2x10m, Keck Observatory, Mauna Kea 4x8m, ESO Very Large Tel., Paranal, Chile 2x8m, Gemini Observatory (Hawaii/Chile) 8m, Subaru (Natl. Astron. Obs of Japan)

Slide 27: 

Multiobject spectroscopy (Gemini-N) Direct image Slit placement Raw multislit spectra Reduced spectrum (AGN at z=3.35)

Adaptive optics : 

Adaptive optics Use “rubber mirror” to correct for atmospheric distortion Brings 8-10m telescopes close to diffraction limit in best cases (especially near-IR) They now outperform HST for some observations Need natural or laser guide stars nearby Gemini-N/Altair 0.26 to 0.06” FWHM 1.65 microns (H)

Submillimeter detectors : 

Submillimeter detectors Precise antennas Cryogenic detector arrays Interferometry This shows us the thermal emission from dust in galaxies at high redshift, even if their direct starlight is completely absorbed

Stellar spectra – the fossil record : 

Stellar spectra – the fossil record Chemistry of stellar surface reflects initial chemical makeup until late in its lifespan Stars’ orbits change only very slowly over time Makeup and motions of stars preserve a detailed record of our galaxy’s history Early stars formed with low heavy-element abundances and in a nearly spherical system

The early galaxy bestiary : 

The early galaxy bestiary Lyman-break galaxies Extremely red objects (EROs) - the oldest young galaxies and dusty environments Star-forming subgalactic objects Submillimeter galaxies Lyman a clouds Quasars and radio galaxies Absorption-line systems These often occur in groupings

Lyman-Break Galaxies (LBGs) : 

Lyman-Break Galaxies (LBGs) Galaxy spectra show a cutoff at 912 A due to absorption by neutral hydrogen This allows a straightforward multicolor selection (blue in two bands, missing shortward of that) Thousands of galaxies at z>2.7 have now been found in this way

The Lyman Break : 

The Lyman Break The Lyman break from satellite UV observations of a star-forming region in the nearby spiral M33 The brightest LBG in the Hubble Deep Field, a clumpy galaxy at z=3.21. 300 nm 450 nm 606 nm 814 nm

Submillimeter-bright Galaxies : 

Submillimeter-bright Galaxies Found at z=2-3 Most powerful early star-forming sites? Key on dust emission, not stars Clump with other high-redshift objects Many have buried quasar cores Background: ionized-gas plume in submm galaxy ELAIS N2 850.4 at z=2.4, from NASA Infrared Telescope Facility, April 2003)

Extremely Red Objects (EROs) : 

Extremely Red Objects (EROs) May be either intrinsically red or reddened by dust absorption; both kinds exist A way to seek the oldest galaxies at a particular redshift, a sensitive probe of when galaxy formation began in earnest

Subgalactic Clumps : 

Subgalactic Clumps Small size, blue color, Lyman a emission Active star formation, low metallicity Evidence for global winds escaping systems Exist in groupings with bright galaxies/AGN Are these the early units predicted by hierarchical schemes (and fitting dark-matter simulations)?

Slide 37: 

Blue subgalactic objects versus nearby spiral M101 at the same ultraviolet emitted wavelength Size: 1 kpc~3000 light-yr Many are double Comparable UV luminosity to bright galaxies now

The early Universe could be crowded(a group at z=2.4) : 

The early Universe could be crowded(a group at z=2.4) Subgalactic objects Quasars Radio galaxy ERO

Quasars in the Early Universe : 

Quasars in the Early Universe Trace supermassive black holes and their growth by accretion Black holes today are ubiquitous in bright galaxies Quasars now seen to 0.5 Gyr after beginning, very common 10 Gyr ago Surrounding gas heavily processed by supernovae, even at highest redshifts

Slide 41: 

Heavy elements in high-redshift quasars HST composite, courtesy W. Zheng)

Ingredients of a cosmic history : 

Ingredients of a cosmic history Gravitational collapse and gas infall Star formation (a feedback process) Heavy-element production Winds and the intergalactic medium Growth of supermassive black holes The first stars – a breed apart

The First Stars (Population III) : 

The First Stars (Population III) Formed of pure hydrogen/helium Very massive (80-300 solar masses) Hot, short-lived Energetic supernova explosions Enriched surrounding gas, disrupted parental gas clouds Enrichment led to “normal” star formation Enriched intergalactic gas as well

New tools, new horizons : 

New tools, new horizons James Webb Space Telescope Adaptive optics spreads in accessibility, field of view, and wavelength Atacama Large Millimeter Array (ALMA) High-dynamic-range simulations of galaxy formation Massive galaxy and star spectroscopic surveys

James Webb Space Telescope (2010) : 

James Webb Space Telescope (2010)

Atacama Large Millimeter Array : 

Atacama Large Millimeter Array

Slide 48: 

CELT/NOAO 30-meter design

Slide 49: 

The giant OWL scans the skies…

Final Musings: The Anthropic View : 

Final Musings: The Anthropic View We require particular physical laws and environmental conditions for life Galaxies provide a place for stars to form and chemically enrich their surroundings Their inception may require a first generation of uniquely massive stars Do we live in the unique Universe, or does it make sense to think of the “Multiverse”?