End of the Cosmic Dark Ages -- the First Galaxies and the Cosmic Renaissance Xiaohui Fan Steward Observatory The University of Arizona

Prelude: an offer from Vera Rubin During the conference “After the Dark Ages: when Galaxies were young” In Oct 1998, near Washington DC…. Martian meteorite: Will be awarded the discoverer of the first redshift higher than seven object… still unclaimed…

A brief cosmic history  Big Bang: the universe filled with hot gas  Cosmic Dark Age: no light no star, no quasar  First light: the first galaxies and quasars in the universe  Cosmic Renaissance: universe lit up by young galaxies and quasars  “reionization” completed, the universe is transpartent and the dark ages ended  today

A brief cosmic history  Big Bang: the universe filled with hot gas  Cosmic Dark Age: no light no star, no quasar  First light: the first galaxies and quasars in the universe  Cosmic Renaissance: universe lit up by young galaxies and quasars  “reionization” completed, the universe is transpartent and the dark ages ended  today

The end of dark ages: Movie

Gnedin 2000 Cold gasLight background Gas densityGas temperature

Gnedin 2000 Cold gasLight background Gas densityGas temperature

Life as a Hydrogen atom at the end of cosmic dark ages

To Study the End of Cosmic Dark Ages is to: Search for the first light  the earliest and most distant galaxies and quasars in the universe Map the history of the cosmic enlightenment  how the light from the first galaxies and quasars transformed the universe from opaque to transparent, “reionize” the universe and ended the cosmic dark ages  The cosmic history in the first billion years after the Big Bang

A tale of Two Maps Sloan Digital Sky Survey – mapping the optical sky –Finding the first quasars –Discovery of Gunn-Peterson effect – shadow of the cosmic dark ages Wilkinson Microwave Anisotropy Probe – mapping the microwave sky –Polarization of the cosmic microwave background – looking through the cosmic dawn

Redshift: measuring distance in cosmology Redshift measures of how fast an object is moving away from us  they are “redder”, or their spectral lines are at longer (redder) wavelength Expansion of the universe  more distant objects move faster away from us, or at “higher redshift” Light from the most distant objects took the longest time to reach us  highest redshift objects are the “youngest, or earliest objects” in the universe Searching for the first objects in the universe  searching for the most distant, highest-redshift galaxies and quasars z~7: –13 billion light years away; –the universe was about 700 million years old; 5% of its current age.

Quest to the Most distant Quasars and Galaxies Z=7: Dr. Rubin’s Meteorite??

What is a Quasar? Quasar – Quasi-Stellar Object (QSO) –Very luminous (100 – 1000 brighter than Milky Way) –Active nucleus at the center of galaxy –Powered by supermassive black holes (millions solar masses) –Radiation from hot gas falling into BH –Among the most distant objects in the universe Ground-based Image: stellar At the center of galaxy Gas and dust surrounding The central BH

Quasar Spectra at Different Redshifts

MAKE A DIGITAL 3-D MAP OF THE UNIVERSE IN 5 YEARAS Main Imaging Survey: 10,000 square degrees ¼ of the whole sky 100 million 5-band images Spectroscopic Survey: brightest 1 million galaxies brightest 100,000 quasars SDSS Technical Goals

The SDSS telescopes are located at Apache Point Observatory (APO) in the Sacramento Mountains of south-central New Mexico. Just down the road is the National Solar Observatory in Sunspot, New Mexico. Both Observatories and a nearby Visitors Center are open to the public. Where is the SDSS?

2.5m Dedicated Telescope: with wide 3 o field-of-view Largest CCD Imaging Camera: 54 large CCD devices, 150 Mega pixels Filters u’g’r’i’z’ ( A) for star/galaxy/QSO selection Data rate: 15 deg/hr; 5MB/s; 170 GB/night; 12 TB total Multiobject Fiber Spectrographs: 640 different objects observed at the same time. Large Volume Data processing: Many terabytes of raw data, processed at Fermilab SDSS Technological Inovations

SDSS 2.5m Telescope SDSS 0.5m Telescope ARC 3.5m Telescope Apache Point Observatory

SDSS 2.5m Telescope

SDSS Imaging Camera Top to bottom: g’ z’ u’ i’ r’

What does the data actually look like?

Plugging Spectroscopic Plates

Participating Institutions: ~100 Scientists Princeton UniversityUniversity of ChicagoFermilab Institute for Advanced StudyJohns Hopkins University University of WashingtonU.S. Naval Observatory Japanese Participation GroupNew Mexico State University Max-Planck A and IA Funding: ~$100 Million Alfred P. Sloan Foundation Member Institutions National Science Foundation (NSF) National Aeronautics and Space Administration (NASA) United States Department of Energy (DOE) Japanese MonbukagakushoThe Max Planck Society Survey Participants

The SDSS Collaboration

How to find the most distant quasars? The highest redshift, most distant quasars are very red  looking for the reddest objects on the sky The highest redshift, most distant quasars are extremely rare  one out of many million objects, and could be confused with many kinds of ‘contaminants’ : brown dwarfs, cosmic ray hits etc.  needles in a haystack  complicated, multi-step searching technique that involves a number of ‘follow-up’ observation using telescopes in addition to the SDSS facilities.

Find the most distant quasars: needles in a haystack 2..Photometric pre-selection: ~200 objects 1.SDSS database: 40 million objects APO 3.5m Calar Alto (Spain) 3.5m 3. Photometric and spectroscopic Identification (~20 objects) 4. Detailed spectra (8 new quasars at z~6 Keck (Hawaii) 10m Hobby-Eberly (Texas) 9.2m

Search for the First Quasars: Results 3000 square degrees of the sky searched 6 telescopes, 10 different instruments used Spent 3 years, ~50 nights of observing time 8 most distant quasars discovered: z=5.74, 5.82, 5.85, , 6.23, 6.28, 6.37

Z~6 quasars from the SDSS Z=5.80Z=5.82 Z=5.99 Z=6.28

New z~6 Quasars from the SDSS z=6.1z=6.2 z=6.4

The most distant quasar: probing the state of universe at the end of the dark ages, by looking at the absorption from cold gas in the quasar spectrum from before the end of the dark ages.

Gnedin 2000 Neutral fractionLight background Gas densityGas temperature

Gunn-Peterson Effect: Shadow of the Dark Ages Gunn-Peterson (1965) effect: –During the dark ages, the universe is opaque to the ultraviolet light due to the cold, neutral hydrogen –Create a absorption TROUGH in the quasar spectrum –Detection of Gunn-Peterson trough signals that we have reached the cosmic “dark-age” and the epoch of the first generation galaxy and quasar formation –One of the longest-sought predictions of cosmology, but never detected until… Lya No G-P trough (still flux detected) G-P trough

VLT/FOS2 T=-0.001±0.003 Detection of A Complete Gunn-Peterson Trough: We have reached The end of the Cosmic dark ages Pentericci et al.

Detection of Gunn-Peterson Trough Tells us: At z~6 (800 million years after the big bang): –The universe is going through a rapid transition Cold  hot Neutral  ionized Opaque  transparent First generation galaxies and quasars have formed –Cosmic Dawn has arrived! the End of the Cosmic Dark Ages Question:  when did this transformation started?  when was the very first star form?  How long did the cosmic renaissance last?

WMAP – Wilkinson Microwave Anisotropy Probe

First detailed full sky CMB map: afterglow of the big bang

Fluctuation on the cosmic micronwave background: finger print of the cosmos

CMB polarization: looking through the cosmic dawn CMB fluctuation: seeds of today’s galaxies and quasars First galaxies and quasars: heated and ionized the universe at the end of the dark ages  cosmic dawn Ionized plasma in cosmic dawn: polarizing the microwave background Amount of polarization  determining the exact onset of the cosmic dawn

Polarization: how it works

Polarization: how do we see it

WMAP: detecting polarization

WMAP Polarization Results CMB is strongly polarized –A lot of hot plasma from the first galaxies and quasars –The first star were formed at about 300 million years after the big bang, starting the cosmic dawn –The cosmic renaissance – the reionization epoch -- lasted for half billion years  the cosmic dark ages didn’t end in one night! However –CMB result is still an indirect result –The very first light has not been detected –The detailed history of cosmic renaissance yet to be mapped out

The Decade of Galaxy Formation In the next 10 – 15 years, a number of large ground-based and space telescope will be built One of the central goal of these telescopes: detecting the first light, probing deep into the cosmic dark age, and mapping of the history of cosmic reionization and formation of first galaxies and quasars

The James-Webb Space Telescope: the first light machine

Atacama Large Millimeter Array: star formation in the early universe

Square Kilometer Array: Detecting Hydrogen in the Dark Ages

Planck: Mapping the reionization history

20-30 meter ground-based telescopes: probing the high- redshift universe

Summary As of 2003, people have discovered galaxies and quasars up to redshift of 6.5, or 13 billion light years away, coming from a time when the universe was only % its current age We believe we have detected the epoch of the end of cosmic dark ages, when the first galaxies and quasars in the universe were forming, and lit up the whole universe In the next two decades, new telescopes, from the ground and in space, will systematically explore the high-redshift universe, likely discovered the first light in the universe and map out the history of the cosmic dark ages.