Probing Cosmic Dawn with

Neutral Hydrogen Joseph Lazio

with thanks to Jack Burns, Tzu-Ching Chang, Aaron

Parsons, Jonathon Pober, Olivier Dore

Brief History of the Universe

Universe starts

in uniform,

largely neutral

state

What happened?

Today, highly

structure and

ionized

Hydrogen Atom

n = 1, F = 1 0

E10 = hn = 5.8743253 µeV

T* = E10/k = 0.068 K

n = 1420.405752 MHz

l = 21 cm

Hydrogen Signal from Cosmic

Dawn and Dark Ages

Dark

Ages

500 MHz 100 50 10 5

50

−50

−100

Tb (m

K)

100 10 1 + z

Neutral Hydrogen 21 cm

spin-flip transition

provides probe of

neutral intergalactic

medium before and

during formation of

first stars

First

Stars

EoR

n = 1420 MHz/(1 + z)

l = 21 cm (1 + z)

H I Fluctuation Power Spectra

CMB

H I

fluctuation

power

spectrum Alvarez et al.

2 10 500

1000

2000

3000

4000

5000

6000

D[µ

K2]

90◦ 18◦

500 1000 1500 2000 2500

Multipole moment,

1◦ 0.2◦ 0.1◦ 0.07◦Angular scale

Measurement Approaches

500 MHz 100 50 10 5

50

−50

−100

Tb (m

K)

100 10 1 + z

Sky-Averaged Spectrum

Fluctuation Power Spectrum

Science Goals of the Astrophysics

Roadmap

Goal 2: How Did We Get

Here?

(Cosmic Origins)

Goal 3: How Does Our

Universe Work?

(Physics of the Cosmos)

Sky-Averaged Spectrum

500 MHz 100 50 10 5

50

−50

−100

Tb (m

K)

100 10 1 + z

Dark Ages Radio

Explorer

Lessons from the Ground

Toward a Probe-class Mission

(Dillon et al. 2015;

Ali et al. 2015)

MoonRise Analog

Toward a Probe-class Mission

New Frontiers mission

concept (Planetary

Sciences)

• Sample return from

South Pole-Aitken

Basin

• < $1B

• ~ 1000 kg

Radio Array Concept Study

Toward a Probe-class Mission

10s of antennas

Free-Flyer?

Toward a Probe-class Mission

…

Harris Corp.

Hydrogen Signal from Cosmic

Dawn and Dark Ages

Dark

Ages

500 MHz 100 50 10 5

50

−50

−100

Tb (m

K)

100 10 1 + z

Neutral Hydrogen 21 cm spin-

flip transition provides probe

of neutral intergalactic

medium before and during

formation of first stars

First

Stars

EoR

Sample Chapter Divider

Portion of radio spectrum relevant for 21 cm

observations of Cosmic Dawn and Dark Ages

• Yellow = reserved for radio astronomy

Radio Spectrum

•Data from Radio Astronomy Explorer-2, when it passed behind the Moon, illustrating cessation of terrestrial emissions

•Apollo command modules lost communications when behind the Moon.

330 Myr since Big Bang

50 Myr since Big Bang

time

rad

io b

rig

htn

ess

RAE-2 behind Moon