From Avi Loeb

reionization

Quest to the Highest Redshift

Difficulties in finding high-z galaxies and quasars

• Faint: m-M ~ 47, even the brightest galaxies need Keck/HST; only the brightest quasars can be detected with large surveys

• Rare: e.g. z~6 quasar surface density is one per 500 sq. deg

• Red: all spectral features shifted to the red part of the spectrum, Ly alpha at 1216x7 = 8500 A, where:– sky is very bright– CCD is very insensitive

• Low surface brightness: SB ~ (1+z)-4 = 1/2400

High-redshift Galaxies/Quasars Searching Technique

• Lyman break technique– Broad-band optical colors– Quasars – 80’s; galaxies – 90’s

• Narrow-band imaging (Lyman alpha emitter)– Galaxies – 80’s

• Slitless Spectroscopy – Wide-area spectroscopy – Looking for strong emission line– Quasars – 70’s; galaxies – now

• Cross-identification with other wavelength– Radio: quasars – 60’s; galaxies – 60’s– X-ray: quasars – 80’s– Submillimeter: galaxies – 90’s

• Serendipity (a.k.s. luck…)– If you are Hy Spinrad (Berkeley) or his student, then it will work…

So how far could each of these techniques go?

• Lyman break:– Quasars: 6.4– Galaxies: 6.6; maybe 10?

• Narrow band imaging – Galaxies: 7.0

• Slitless spectroscopy– Quasars: 4.7– Galaxies: 6.5

• Cross-identification– Quasars: 6.1 (radio)– Galaxies: 5.2 (radio)

• Luck:– Quasars: 4.3– Galaxies: 5.5

Lyman Break Galaxies I:Spectrum of high-z galaxies

Lyman break galaxies II:Colors of LBG

Key: The presence of absorption at lambda < 1216A in the rest-frame UV of the galaxy produces a BREAK in the observed high-z galaxy spectrum: LYMAN BREAKby looking for “drop-out” objects in broad-band colors as a result of the Lyman break, we can find high-redshift galaxies!

Lyman break galaxies III:color selection

Narrow-band Imaging

• Idea:– Young galaxies are dominated by young stars and star

forming regions

– With strong HII regions and strong Ly alpha emission lines

– Looking for Lyman alpha line by looking for enhancement in the flux within narrow filters

– High success rate, but still needs follow-up spectroscopy to eliminate contaminants: strong emission lines other than Ly-alpha

Matching towards high-z

The most distant galaxy known to date z=6.98

Even higher redshifts

Z~10?

The new highest redshift record?

Lyman Emitter at z~10?

• Keck blind spectroscopic survey along critical lines of high-z clusters

– Six promising Ly emitter candidates at z=8.7 - 10.2

– Limit of ground-based search; extremely difficult to confirm spectroscopically

Stark, Ellis et al.

The history of star formation in the universe

• Estimating star formation in a galaxy– Roughly proportional to the UV flux UV flux comes

from young, hot stars

– Roughly proportional to the Lyman alpha flux Lyman alpha emission comes from HII regions around young, hot stars

• Madau plot:– Star formation volume density (including all galaxies)

as a function of redshift

– Rapid increase from z=0 to 1.5

– Slow decline at z>2

46,420 Quasars from the SDSS Data Release Three

wavelength4000 A 9000 A

reds

hift

0

1

2

3

5

Ly

CIV

CIIIMgII

HOIII

FeII

FeII

Ly forest

30 at z>660 at z>5.5>100 at z>5

Quasar Evolution at z~6

• Strong density evolution

– Density declines by a factor of ~40 from between z~2.5 and z~6

• Black hole mass measurements

– MBH~109-10 Msun

– Mhalo ~ 1012-13 Msun

– rare, 5-6 sigma peaks at z~6 (density of 1 per Gpc3)

• Quasars accreting at maximum rate

– Quasar luminosity consistent with Eddington limit

Fan et al. 2006, 2010

Quest to the Highest Redshift

080913

050904

090423

000131

970228

GRBs

z=8.2 GRB

A brief cosmic historyBig 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 universeCosmic Renaissance: universe lit up

by young galaxies and quasars “reionization” completed, the universe is transpartent and the dark ages ended

today

A brief cosmic historyBig 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 universeCosmic Renaissance: universe lit up

by young galaxies and quasars “reionization” completed, the universe is transpartent and the dark ages ended

today

When did 1-sigma peak collapse

Cooling Rate of Primordial Gas

n=0.045 cm^-3

Atomic cooling

H_2 cooling

1-sigma

2-sigma

3-sigma

Atomic cooling

H_2 cooling

2-sigma

Collapse Redshift of Halos

Binding Energy of Dark Matter Halos

1-sigma 2-sigma

3-sigma

Supernova

Emergence of the First Star Clusters

molecular hydrogen

Yoshida et al. 2003

Z=30

First star simulation

Fate of first stars

Massive Accretion by Metal-Free Proto-StarsMassive Accretion by Metal-Free Proto-Stars

25pc 0.5pc

Bromm & Loeb

Simulation of a Hypernova Explosion

100 pc

Heavy elements

The end of dark ages: Movie

Reionization

• After recombination, the universe was neutral• At z~20 – 30, the first generation galaxies and

mini quasars formed• At z~6 – 15, the UV radiation from the first

generation objects ionized most of the HI in the universe– The neutral fraction of the universe changed from 1 to

10^-5 (phase transition in ionization state)– The temperature of the IGM electrons changed from

CMB temperature to 10^4 (phase transition accompanied by temperature change)

– IGM becomes transparent to UV radiation, the universe is like a giant HII region (temperature change accompanied by opacity change)

Gnedin 2000

Neutral fraction Light background

Gas density

Gas temperature

Three stages

Pre-overlap

Overlap

Post-overlap

From Haiman & Loeb