The Most Distant Quasars: Probing the End of Cosmic Dark Ages

1
The Most Distant QuasarsProbing the End of
Cosmic Dark Ages

• Xiaohui Fan
• Steward Observatory
• The University of Arizona

2
The SDSS Collaboration
3
40 Years AgoFirst Quasar 3C 273 by Maarten
Schmidt
4
Quasars as Cosmology Probes

• The Study of Highest-Redshift Quasars Probes
• The epoch of first generation of
  galaxies/quasars
  
• Models of black hole formation
• Role of quasar/BH activity in galaxy evolution
• evolution of intergalactic medium
• History of reionization ? probing the end of
  cosmic dark ages
  

5
Exploring the Edge of the Universe

6
SDSS at Your Service
Courtesy of Arizona graduate students
7
The HighestRedshift Quasars Today

• z4 700 known
• z5 30
• z6 6
• Highest redshift
• z6.42

Total Discoveries
SDSS Discoveries
8
Sloan Digital Sky Survey
MAKE A DIGITAL 3-D MAP OF THE UNIVERSE IN 5 Y
EARAS

• 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

9
SDSS Overview

• Primary Telescope 2.5m wide-field (2.5 deg)
• Imaging Survey (wide-field 54 CCD imager)
• Main Survey 10000 deg2
• Five bands, 3000 10000 Å
• rlim 22.5, zlim 20.5
• Spectroscopic Survey
• 106 galaxies (r
• 105 quasars ( 0
• Interesting stars, radio/x-ray sources etc.

10

17,000 Quasars from the SDSS Data Release One
5
Ly a
3
2
CIV
redshift
CIII
1
MgII
OIII
Ha
0
wavelength
4000 A
9000 A
11
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 ? the wide-field,
  deep images of the sky from the SDSS
  complicated, multi-step searching technique that
  involves a number of follow-up observation
  using other telescopes in addition to the SDSS

12
Find the most distant quasarsneedles in a
haystack
Hobby-Eberly 9.2m
APO 3.5m
Kitt Peak 4m
Calar Alto (Spain) 3.5m
Keck 10m

• SDSS database
• 100 million objects

MMT 6.5m
4. Detailed spectra (12 new quasars at z6)
2..Photometric pre-selection 500 objects
3. Photometric and spectroscopic
Identification (50 objects)
13
Z6 quasars from the SDSS
Z5.80
Z5.82
Z5.99
Z6.28
14
New z6 Quasars from the SDSS
z6.1
z6.2
z6.4
15
(No Transcript)
16
Quasar Density at z6

• Density of high-z quasars
• Density declines by a factor of 20 from z3
• The growth of the earliest supermassive BHs
• Cosmological implication
• MBH109-10 Msun
• How to form such massive galaxies and assemble
  such massive BHs in less than 1Gyr??
  
• The rarest and the most massive systems at early
  times
  
• the initial assembly of the system must start at
  z10
  
• ? co-formation and co-evolution of the earliest
  SBH and galaxies
  

Fan et al. in prep.
17

• Submm and CO detection
• in the highest-redshift quasar
• Dust mass 108 109Msun
• H2 mass 1010Msun
• Star forming rate 103/yr
• co-formation of SBH and
• young galaxies

18
A brief cosmic history

• recombination

• Cosmic Dark Ages no light
• no star, no quasar IGM HI

• First light the first galaxies
• and quasars in the universe

• Epoch of reionization radiation from the first
  object lit up and ionize IGM HI ? HII

? reionization completed, the universe is trans
parent and
the dark ages ended
? today
Courtesy G. Djorgovski
19
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 hydrogen
  gas
  
• Create a absorption in the light spectrum of
  quasar
  
• Detection of Gunn-Peterson effect signals that we
  have reached the end of the cosmic dark-ages
  and the epoch of the first generation galaxy and
  quasar formation
• One of the longest-sought predictions of
  cosmology, but never detected until

20
Neutral fraction
UV background
Gnedin 2000
Gas density
Gas temperature
21
The end of dark ages Movie
Courtesy of N. Gnedin
22
VLT/FOS2
Pentericci et al. 2002

23
Gunn-Peterson troughs confirmed by new z6 quasars
24
Comparing with Models
Light background
Fraction of Neutral H
Mass-averaged
postoverlap
overlapping epoch
Pre- overlap
Volume-averageed
Fan et al. 2002
25

The detection of Gunn- Peterson trough indicates
that z6 marks the tail end of the
reionization process and therefore the very end
of the cosmic dark ages.
26
Detection of Gunn-Peterson Trough Tells us

• At z6 (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?