Transcript A 20/20 vision of Reionization and Galaxy formation Sangeeta Malhotra School of Earth and Space Exploration Arizona State University.

A 20/20 vision of Reionization and
Galaxy formation
Sangeeta Malhotra
School of Earth and Space Exploration
Arizona State University.
Why Reionization?
• As a watermark
for galaxyformation:
– 10 ionizing
photons per
Baryon produced
by galaxies.
Why Reionization?
• Thermal history of the universe requires it:
– Expansion and adiabatic cooling implies recombination
of the IGM at z ~ 1100.
– Transmission of UV light from nearby quasars requires
a largely ionized IGM at z ~ 0 (indeed, up to z ~ 6).
• Reionization sources:
– Stars- likely
– First stars- possible
– AGN- currently disfavored
• Studying the history of reionization sheds light on
the history of early star formation.
Two methods of identifying High redshift
galaxies
Lyman-break galaxies
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Lyman- galaxies
Slitless spectroscopy
Qui ckTime™ and a
TIFF (LZW) decompr essor
are needed to see this pictur e.
If you were to look at high redshift (z > 6)
galaxies with your naked eyes. This is what they
would look like:
To see galaxies in the Era of reionization, we
need to
1. Go to the infra red.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
2.
Go faint
OH forest from the ground
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
3. Have high spatial resolution
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Extrapolation to z~10
Ferguson et al. 2004
4. Have wide-field surveys
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Ouchi et al 05
LSS at z = 5.7
5. Get Spectra to get rid of foreground
objects
Malhotra et al. 2005, Pirzkal et al. 2007.
Things to argue about:
• Luminosity function of
z~6 galaxies: slope of the
faint end - whether or not
there are sufficient
photons to do the
reionization? (Bunker et
al. 04, Yan & Windhorst
04, Malhotra 05)
• Does the number of
galaxies go up at z > 6
(Bouwens & Illingworth
2006, Stark et al. 2007)
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Bouwens & Illingworth 2006
Stark et al. 07
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Masses of old stars on z~6 galaxies:
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Low mass, young
ages for Lyman-
galaxies.
(Pirzkal et al. 2007)
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Massive LBGs: Mobasher et al. 06, Wiklind et al 07, Egami et
al. 2005
When was reionization?
• Z~6 from Gunn-Peterson effect
• Z~11 from WMAP3
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
• Z > 6.5 from Lyman- galaxies
• Z ? From 21 cm tomography
The Lyman- Test
Neutral IGM
Continuum
Photons
To
Observer
Young starburst
Lyman-
photons
(Miralda-Escude 1998; Miralda-Escude & Rees 1998;
Haiman & Spaans 1999; Loeb & Rybicki 1999)
Comparing the Tests
Gunn-Peterson
CMBR
Polarization
Lyman α
21 cm
10-4
0.5 or so
0.1
0.5 or so
In nonuniform 10-2
IGM
0.5 or so
0.3-0.5
0.5 or so
Source
properties
Very rare,
bright.
Everywhere
Common, faint.
Everywhere
Mapping
region
Local along 1D
line of sight
“Global” integral
constraint
Local, 2D, or 3D
with redshifts, 1
pMpc smoothing.
Statistical -->
local in 3D later
Redshift
coverage
Continuous.
All redshifts
simultaneously
Discrete from
ground;
continuous above
atmosphere.
Depends on
RFI? Hopefully
continuous
Threshold
neutral
fraction
uniform IGM
Reionization Test
Malhotra & Rhoads 2004, ApJ Letters 617, L5;
See also Stern et al 2005; Haiman & Cen 2005; Kashikawa et al 2006
• We constructed Ly-α
luminosity functions at
z=5.7 and z=6.5 from a
variety of surveys (including
work from LALA, Hu et al, Kodaira et
al, Taniguchi et al, Santos et al, Ajiki et
al, Tran et al, Martin & Sawicki.)
Lyman-α Luminosity Functions
• Luminosity function fits
for three faint-end
slopes.
• z = 6.5 plot shows two
null hypotheses:
– z = 5.7 LF, or
– z = 5.7 LF reduced by a
factor of 3 in
luminosity to
approximate IGM
absorption.
• No evidence for neutral
IGM!
Malhotra & Rhoads 2004, ApJ Letters 617, L5
The volume test:
(Malhotra & Rhoads, 2006)
Suppose each Lyman- emitter is visible because of a local
Stromgren sphere, created by neighboring undetected dwarf
galaxies, hidden AGNs, decaying dark matter, tooth fairies …
•
•
•
•
•
We know the space density of Lyman- galaxies
at z=6.5
 > 1x10-4 cMpc-3 (Taniguchi et al. 2005)
Place each one in a ionized bubble of the
smallest size to enable escape of half of the line
flux in an otherwise neutral medium
– [V(I)] > 4/3(RssMpc)3
Get a filling factor: f = n V.
The required volume ionized fraction is
then roughly 1 - exp(-f).
Correlations modify the higher order
terms.
Ly- Luminosity Functions Revisited
• Kashikawa et al (2006)
and Shimasaku et al
(2006) have revisited the
LyA luminosity functions
at z=6.5 and z=5.7.
• Find apparent bright end
evolution. Interpretation:
– Neutral IGM? But: LF
shape change not as
expected
– True LF evolution (Dijkstra
et al 2007)?
– Field to field variations?
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Kashikawa et al see some evolution (2006)
• They see evolution at the bright
end of the luminosity function:
3sigma, 2sigma if you take into
account large scale clustering
seen at z=3.
• Not significant if clustering
becomes stronger as expected
theoretically (Dijkstra, Wyithe,
Haiman 2006)
Ly- Luminosity Functions Revisited
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
The z=5.7 LF from Shimasaku et al is the highest yet observed.
If we compared z=6.5 from K06 to any other z=5.7 LF, the difference
would be smaller... Field to field variations?
New questions that we have not yet asked
• Morphology: HST has shown fairly compact (but not point
like) morphology, Morphology in the line different from
continuum: radiative transfer
• Slope of the Faint end of the luminosity function: dwarfs
• Blobs: cold accretion of gas in galaxies that are forming: can
we see that?
• Spectral Energy Distribution of galaxies: know little about
the continuum properties
• Spectra: physical properties, extinction, metallicities, SF
history.
• Go to higher redshift and look for signatures of reionization,
manifested as attenuation of Ly-a line.
Cold accretion flows
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Mapping Ionized and Neutral Gas with
Lyman Alpha Galaxies
• A control sample of Lyman break selected galaxies will be
useful (green dots, below).
9 square-degrees of grism observations
should yield about 1-4x105galaxies between z = 713, with redshifts
Should be capable of
detecting large scale structure