Exploring the Depths of the Universe
Jennifer Lotz
Hubble Science Briefing
Jan. 16, 2014
Hubble is now observing galaxies
97% of the way back to the Big Bang,
during the first 500 million years
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Challenge: Can we peer deeper into the Universe
than the Hubble Ultra Deep Field
before the launch of the James Webb Space Telescope?
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Extragalactic Astronomy 101
1. the speed of light is finite ⇒
distance = look-back time
2. the universe is expanding ⇒
distance = velocity
3. objects moving away from us look redder ⇒
redshift = distance = look-back time
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1. distance = time
the Sun
8 minutes
Andromeda
3 million years
Earth
13 billion years
distant galaxy
13.7 billion years
We see distant objects as they were in the past
because their light takes a long time to reach us
echo of the Big Bang
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2. distance = velocity
• the universe is expanding –
Velocity away from our galaxy 
objects farther away are moving away faster
Distance from our galaxy 
Hubble 1929
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3. velocity = redshift
redshift = distance = time
velocity
N. Wright / www.astro.ucla.edu
The light from objects moving away from us
is shifted redward.
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distant galaxy
Galaxy redshifts are
primarily due to
expansion of space,
not Doppler shift
Earth
Emitted blue light…
Expanding universe
stretches light
to longer wavelengths
Redshift z =
stretch factor
minus one
…stretched to green…
…then red (or even infrared) when observed
ESO animation:
http://www.eso.org/public/videos/redshiftv/
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(4. Astronomer’s unit of brightness)
Astronomers measure brightness
in “magnitudes”
Larger magnitudes are fainter
(backwards!)
Fainter 
Magnitude = -2.5 log10(brightness)
Faintest star the human eye can see is
6th magnitude
Hubble Ultra Deep Field reaches
30th magnitude
= a factor of 4 billion times fainter
than what we can see with naked eye
Frontier Fields reaches ~10x fainter
than Ultra Deep Field
= 40 billion times fainter than human
eye can see.
Figure from http://sci.esa.int/education/35616-stellar-distances/
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visible light
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when the universe was young..
blue = 0.0 K
green = 2.7 K
red = 4.0 K
380,000 years after the Big Bang
NASA/WMAP Science team
microwaves
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When the universe was young...
blue = 2.7249 K
green = 2.7250 K
red = 2.7251 K
380,000 years after the Big Bang
NASA/WMAP Science team
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from the Big Bang to the Milky Way
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The Hubble Deep Field - 1995
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The Hubble Deep Field South- 1998
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The Hubble Ultra Deep Field -2004
new camera on Hubble = new deep field
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Science Highlights from Deep Fields
•
detection of faint galaxies at look-back times < 1 billion years
after the Big Bang
 “cosmic star-formation history” peaked ~ 10 billion years ago
•
Galaxies grew in size and mass over this time, and changed
their shapes from irregular to smooth
•
Most distant supernovae used to measure distance, confirm
accelerating universe
•
Accreting supermassive black holes are found in galaxies at
look-back times as early as 10-12 billion years ago.
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How far away are galaxies?
Hydrogen atom excitation levels
Hydrogen atoms absorbs ultraviolet light from
distant galaxies; this “Lyman break” is used to
estimate their redshift.
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The Hubble Ultra Deep Field -2009/2012
new camera on Hubble = new deep field
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The Hubble Ultra Deep Field -2009/2012
Cosmic star formation density 
deep infrared images
needed to
detect the highest
redshift galaxies
Redshift/time since Big Bang 
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most distant
galaxy candidate
NASA/HST the Ultra Deep Field
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Challenge: Can we peer deeper into the Universe
than the Hubble Ultra Deep Field
before the launch of the James Webb Space Telescope?
posed to the Hubble Deep Fields Initiative science working group to
develop an ambitious new “community” deep fields program
HUDF
ACS (optical) = 416 orbits
WFC3 (IR) = 163 orbits
=579 orbits of HST
Gravitational lensing in action
Credit: Ann Feild (STScI)
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Gravitational Lensing
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Wine Glass
Lensing
Phil Marshall
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Challenge: Can we peer deeper into the Universe
than the Hubble Ultra Deep Field
before the launch of the James Webb Space Telescope?
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Answer:
Use Einstein’s theory of general
relativity - “gravitational lensing” - to
go intrinsically deeper than the
Ultra Deep Field.
Gravitational lensing magnifies and stretches light
from distant galaxies behind massive clusters,
making them appear brighter and larger.
Six very massive clusters of galaxies chosen as the
best “zoom lenses”, with input from community.
The Frontier Fields are being observed by NASA’s Great
Observatories - Hubble, Spitzer, and Chandra - over the next 3 years.
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Frontier Fields will also observe 6 fields in parallel with the clusters,
the second deepest observations of ‘blank’ fields ever obtained.
Simultaneous images are taken with Hubble’s infrared camera WFC3/IR
and the optical camera ACS; cameras will swap positions ~6 months later.
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Deep observations of the Frontier Fields will:
• probe galaxies 10-20x intrinsically fainter than any seen before,
particularly those in the first billion years of the Universe
• study the early formation histories of galaxies intrinsically
faint enough to be the early progenitors of the Milky Way
• study internal properties of highly-magnified galaxies
at high spatial resolutions
• provide a statistical picture of galaxy formation at early times
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Deep observations of the Frontier Fields will:
+ map out dark matter, substructure in clusters
+ use 100s of multiple images as probe of distance, DE
+ search for (lensed) SN, transients in distant universe
+ deep and high-spatial resolution studies of z~1-4 galaxies,
(UV escape fraction, sub-kpc structures and star-formation)
+ search for trans-Neptunian objects in solar system
+ give parallaxes of Milky Way stars
+ ???
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Spitzer Frontier Fields
Infrared Spitzer Space Telescope will look at Frontier Fields
in 2 filters redder than Hubble can see
to depths of ~26.5 magnitude
Spitzer crucial for confirming the distant galaxies,
measuring their total stellar masses
http://irsa.ipac.caltech.edu/data/SPITZER/Frontier/
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Chandra Frontier Fields
MACS0717.5+3745
C. Jones-Forman
MACS0416.1-2403
S. Murray
X-ray detect hot cluster gas  cluster mass
and background accreting black holes
archival Chandra data available for all of Frontier Fields;
Chandra FOV encompasses both cluster + parallel fields
new observations began this fall
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HST Frontier Fields: Clusters
Avoid dusty, bright regions of sky;
visible from south (ALMA) and north (Mauna Kea)
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HST Frontier Fields
MACSJ0416.1-2403
Abell 2744
MACSJ1149.5+2223.
Abell370
MACSJ0717.5+3745
Abell S1063
Hubble will observe 2 cluster per year, over 3 years
140 orbits per cluster
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Abell 2744 - HST Epoch 1 completed November 2013
Cluster
Parallel ‘Blank’ Field
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Abell 2744 - HST Epoch 1 completed November 2013
Cluster
Parallel ‘Blank’ Field
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Abell 2744
Parallel ‘Blank’ Field
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Abell 2744
Cluster
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Abell 2744
Cluster
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Abell 2744
Cluster
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Abell 2744
Cluster
a model of the cluster’s ‘optics’ gives us the magnification power
model credit: J. Richard, CATS team
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background galaxies are magnified by factors up to ~10-20,
providing the deepest yet view of the universe
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lensed galaxies
background galaxies are magnified by factors up to ~10-20,
providing the deepest yet view of the universe
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Abell 2744 + parallels are very very deep
Fainter 
Number of galaxies
Number of galaxies
Fainter 
Optical ACS images (blue, green, yellow) reach ~29th magnitude (dashed line)
Infrared WFC3/IR images (orange, pink, red, dark-red) >~28.7 magnitude
(observed magnitudes, not intrinsic magnitudes)
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Deepest view yet into the distant universe:
Observed Fainter 
Intrinsically Fainter 
HUDF12
Number of galaxies
HUDF12
Take observed fluxes x lensing magnifications (average ~1.8x, max ~80x)
⇒ intrinsically faintest Frontier Fields galaxies ~2.5 magnitudes (10x) fainter than
Ultra Deep Field (blue dashed line)
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Exploring the Depths of the Universe
• The Frontier Fields is combining the power of nature’s telescopes - massive
clusters of galaxies - with HST to provide the intrinsically deepest view of the universe
yet. Parallel imaging is providing the second deepest observations of ‘blank fields’,
and improve our statistical understanding of most distant and faint galaxies.
• NASA’s Great Observatories -- Hubble, Spitzer, and Chandra - will observe the
Frontier Field clusters and parallel fields over the next 3 years.
•
The first set of Hubble observations of Abell 2744 are complete, and images have
been publicly released. These reveal thousands of distant galaxies, many at intrinsic
luminosities ~10 times fainter than ever seen before.
http://www.stsci.edu/hst/campaigns/frontier-fields
http://frontierfields.wordpress.com/
https://www.facebook.com/FrontierFields
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Exploring the Depths of the Universe
Jennifer Lotz, Matt Mountain,
& the Frontier Fields Team
Space Telescope Science Institute,Spitzer Science Center
www.stsci.edu/hst/campaigns/frontier-fields
contact: lotz@stsci.edu
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