1. 21cm
cosmology
Ue-­‐Li
Pen
K.
Masui,
E.
Switzer,
R.
Shaw,
L.
Cailin,
G.
Paciga,
K.
Bandura,
J.
Peterson,
T.
Chang,
Y.
Liao,
X.
Chen,
Y.
Li,
T.
Voytek,
A.
Natarajan,
M.
Dobbs,
M.
Halpern,
J.R.
Bond,
G.
Hinshaw,
J.
Roy,
Y.
Gupta,
R.
Nityananda,
and
many
more

2. Overview
21cm
physics
Theory:
dark
energy,
gravity
waves,
neutrinos,
enhanced
21cm
pre-­‐reionizaTon
structures.
ObservaTons:
first
detecTons
and
upper
bounds
(GBT,
GMRT)
Future:
dedicated
surveys
(CRT,
CHIME,
etc
)

3. 21cm:
HI
hyperfine
transiTon
• Hyperfine
transiTon
when
electron
and
proton
spins
flip:
change
in
magneTc
moment
• h
ν
=α4
me
c2
(me/mp)
• ν=1420.40575
MHz
• Highly
forbidden,
lifeTme
t~107
years
• Astronomical
Tme
scales
T>>t

4. ApplicaTons
Hydrogen
Maser
Clock
Milky
way
mapping
Nearby
redshif
surveys
(HIPASS,
ALFALFA)
Cosmological
redshif
surveys
(GBT,
CHIME/CRT/
Tianlai)
High
redshif
universe
(GMRT/LOFAR/MWA/
PAPER)

5. 21cm sky at z=0
Kalberla et al 2005, from WMAP LAMBDA

6. Image courtesy of
NRAO/AUI and
Chung et al.,
Columbia
University

7. Atomic
physics
-­‐-­‐
energy
splihng=0.068K<<TCMB.
-­‐-­‐
Emission/absorpTon
depends
on
spin
temperature
TS
-­‐-­‐
Typically
collisionally/uv
excited.
-­‐-­‐
for
TS
>>
TCMB,
emissivity
independent
of
TS:
measure
hydrogen
(HI)
mass
robustly.

8. 21cm:
emission
δ Tb=τ TS = const

9. Spin
evoluTon
Furlanetto Oh & Briggs, 2006

10. 21cm:
observaTons
• Hydrogen
is
the
most
abundant
element
in
the
universe
• 21cm
line
opTcally
thin
from
the
ground
over
most
lines
of
sight
to
very
high
z
(~100)

11. 21cm:
observaTonal
challenges
• Inverse
square
law:
required
collecTng
area
proporTonal
to
distance2.
• Highest
redshif
direct
galaxy
detecTons
at
z~0.2
using
2000
hours
of
WSRT
(5000m2)
• For
cosmological
interests
(1<z<100)
and
wide
sky
maps
needs
km2
array:
SKA

12. Technical
challenges
• SensiTvity:
bigger
telescopes?
• Foreground
contaminaTon:
design/analysis?
• Target:
Galaxies,
Intensity
Mapping/BAO,
EoR?

13. The
21
cm
universe
• Cosmological
LSS
treasure
trove
(UP04,
Loeb&Zaldarriaga
04,
Lewis&Challinor
07,
EoR:
etc)
GMRT/
• Up
to
1018
modes:
LOFAR
(Jeans/Hubble)3
CHIME/
GBT MWA
• Physics:
Lensing,
gravity
waves,
Paper
primordial
NG,
BAO,
SDSS
AP
• GW
to
r
~
10-­‐8
•
fNL~
10-­‐4
• Astrophysics:
EoR,
galaxy
evoluTon
• Experiments
NOW
Tegmark &

14. Fundamental
Physics
• 0<z<2:
dark
energy,
BAO,
w-­‐w'
• z>2:
Large
angle
lensing:
modified
gravity
(Lu
&
UP
2009,
Masui
et
al
2010)
• z>10:
gravitaTonal
waves

15. Intensity
Mapping
• Stars
get
fainter
with
distance:
hard
to
see
individually
at
cosmological
distance.
Galaxies
sTll
visible.
• Galaxies
get
fainter
with
distance:
hard
to
see
in
HI.
Large
scale
structure
sTll
visible?
• Large
scale
structure
is
LARGE:
degree
scale.
High
resoluTon
not
needed.
• Modest
size,
monolithic
radio
telescopes
needed.
(CPPM
2008,
Wyithe&Loeb
2008)

16. From: talk by O. Lahav

17. Foreground:
GalacTc
Synchrotron
Haslam 408 MHz Much brighter than signal, but no spectral structure

18. Robert
C
Byrd
Telescope:
100m

19. HI
content
at
z=0.8
Cross-­‐correlaTng
GBT
HI
&
DEEP2
opTcal
galaxies
at
z
~
0.7-­‐1.1
(Chang
et
al,
Nature
2010)
GBT radio
continuum
sources + HI
GBT HI
DEEP2
density

20. • Measure HI &
optical cross-
correlation on 9
Mpc (spatial) x 2
Mpc (redshift)
comoving scales
• HI brightness
temperature on
these scales at
z=0.8:
•
• Highest-redshift
detection of HI in
emission at 4-
Chang, Pen, Bandura, Peterson, Nature, sigma statistical
2010
significance.

22. GBT 15h auto power

23. IniTal
Intensity
Mapping
• Detected
collecTve
large
scale
structure
with
100h
of
GBT
Tme:
first
demonstraTon
of
distant
IM.
No
individual
galaxies
detected,
many
galaxies
per
resoluTon
element
• Proposal
submited
for
z=1
BAO
survey
on
4
pixel
array
at
GBT

24. Baryon
AcousTc
OscillaTons
–
Dark
Energy
Probe
• CMB
acousTc
oscillaTons:
imprinted
standard
ruler,
100
Mpc.
• Present
in
current
mater
distribuTon
• KinemaTc
metric
WMAP5
and
other,
Nolta
et
al
of
universe
(2008)

25. Present
LSS
BAO
DetecTons
2007
Percival
et
al
2005
Eisenstein
et
al
• Percival
et
al
2007

26. Blake et al 2011: WiggleZ, z~0.6 Masui et al: GBT-BAO
proposal 2012, z~1

27. Dedicated
Survey
Experiment
• Low
frequency
technology
cheap,
modest
size:
(100
m)2
to
z<2
• Large
field
of
view:
receiver
arrays
• High
surface
brightness
sensiTvity:
compact
arrays
• Stable,
reliable:
no
moving
parts
• Technologies:
aperture
arrays
(Wyithe,
Loeb,
Geil
2008),
cylinders
(Peterson
et
al)

28. Darwin
AUSTRALIA
Brisbane
Perth
Sydney
Melbourne
+
Adelaide
Canberra
Molonglo
Hobart
Northern
Cross
Molonglo
Ooty
Cambridge
Pushchino

29. CMU
cylinder
in
operaTon:
J.
Peterson,
U.
Pen,
U.
Seljak,
K.
Bandura,
K.
Sigurdson

30. Fast Fourier Transform Telescope
CHIME, Tianlai, CRT, etc

31. New
Cylinder
Radio
Telescopes
Canada,
US,
China,
France,
Morocco
Map
the
Hubble
volume
to
0.8<z<2.5
Most
sensiTve
BAO,
RSD,
lensing
survey
Ancillary
science:
21cm
absorbers,
radio
transients,
pulsar
search/monitoring,
magneTc
fields
Scalable
to
z~20:
tens
of
square
kilometers

32. Gravity
Waves
• Masui
&
Pen
2010
(PRL
105,
161302)
• Analogous
to
lensing:
shearing
of
cosmic
structure.
• Fossil
memory
effect:
h~10-­‐6
(inflaTon)
• Measure
r,nT
at
z~15
• Requires
1/h2
modes
• Separates
from
lensing:
transverse
traceless
• Structures
available
to
k~10-­‐3-­‐103:horizon
to
Jeans
scale,
~1018
modes,
peaks
at
z~15

33. Linear
gravity
wave
memory
• GW
in
iniTal
condiTon,
then
redshifs
away

34. Detectability

35. Conclusions
• 21cm
cosmology:
probes
of
dark
energy
(BAO),
modified
gravity
(lensing),
InflaTon
(tensor
modes),
etc.
Beyond
intrinsic
power
spectrum.
PotenTal
measure
of
gravity
waves.
• Intensity
Mapping:
21cm
unresolved
galaxies,
accessible
in
redshif
desert
z=1-­‐3,
iniTal
HI
detecTon
and
surveys
with
GBT
at
z~1.
Upper
bounds
at
z=9.
• Prototypes
and
observaTons
under
way.
Cylinder
telescopes
a
promising
technology
for
fast,
large,
economic
surveys.
OpTmal
calibraTon
and
dynamic
range.