Transcript Galaxies at Cosmic Dawn Revealed in the First Year of the

A Look Back:
Galaxies at Cosmic Dawn
Revealed in the First Year of the
Hubble Frontier Fields Initiative
Dr. Gabriel Brammer (ESA/AURA, STScI)
Hubble Science Briefing / November 6, 2014
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The Early Universe
As observed in the Cosmic Microwave Background Radiation (CMBR),
structure in the universe 300,000 years after the Big Bang consisted of
tiny density fluctuations (1 in 100,000)
Graphic credit: Le Figaro
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A universe in a box
Start with the initial conditions determined from the cosmic
microwave background and let gravity do its thing….
z=4
time ⇒
z=2
z=1
z=0 (today)
Dark Matter
Gas
http://www.illustris-project.org
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Galaxies today
z=4
z=2
z=1
z=0 (today)
Dark Matter
time ⇒
Gas
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Galaxies today
The local galaxy population:
Sloan Digital Sky Survey (SDSS)
z=4
z=2
z=1
z=0 (today)
Dark Matter
time ⇒
Gas
ESA PR 53808
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Cosmology and galaxy evolution
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•
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Galaxies in the expanding universe flying apart (E. Hubble)
causing the wavelengths of light from distant galaxies to be
shifted redward ⇒ “redshift”, or “z”
Given the cosmological model supported by the CMBR and
many other observations (e.g., supernovae), the
measurement of a galaxy’s redshift is both a ruler (how far
is it from us?) and a clock (what was the age of the
universe when the light we observe was emitted?)
To build up an understanding of how galaxies form and
evolve, we observe and characterize the galaxy population
at different redshifts, which correspond to different epochs
in the history of the universe
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Galaxy evolution
Relative surface brightness
(SDSS @ z=0.1 ≡ 1)
Angular size of the Sun’s orbit in
the Milky Way
(8 kpc, in arcseconds)
A problem: distant galaxies are faint and small!
z = 0, today
13.7 Gyr after Big Bang
Redshift, z
900 Myr after Big Bang
(Gyr: giga/billions, Myr: mega/millions of years)
Redshift, z
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Galaxy evolution
The Hubble Space Telescope provides
the needed sensitivity and image
quality to detect distant galaxies
1995
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We can measure the total star
formation history of the universe in
deep Hubble observations!
Stars formed per year, per unit volume
1995
P. Madau et al. (1996)
Redshift, z
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Servicing HST: pushing ever further from
“cosmic high noon” to “cosmic dawn”
Installing Wide-Field Camera 3, 2009 (NASA)
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Stars formed per year, per unit volume
2004
1995
Redshift, z
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2004
Stars formed per year, per unit volume
1995
2009-2012
P. Oesch et al. (2014)
Redshift, z
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2004
Stars formed per year, per unit volume
1995
2009-2012
P. Oesch et al. (2014)
“Dawn”
“High noon”
Redshift, z
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⇐ time
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The next step?
How can we use Hubble to efficiently and significantly go
beyond the large investments of the existing deep fields today,
before the launch of the James Webb Space Telescope in 2018?
⇐ time
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Natural telescopes: gravitational lenses
Massive galaxy cluster
The Hubble Ultra Deep Field + (A million-billion
times the mass of the sun in stars+gas+dark matter)
Illustration by D. Coe, Z. Levay
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Natural telescopes: gravitational lenses
Distortion and magnification of the
=
distant galaxies behind the cluster
Illustration by D. Coe, Z. Levay
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The HST Frontier Fields, year 1
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Abell 2744
Cluster
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Abell 2744
Cluster
“Parallel”
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Scientific collaboration
The first year of Frontier Fields observations has
formed the basis of more than 30 publications
with coauthors from 18 countries
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Science highlights
1. Improved determination of the dark matter distribution and
total mass of the clusters themselves
2. “Ghost light” from galaxies torn apart in the Abell 2744 cluster
3. Numerous galaxy candidates at z > 7
4. A robust, multiply-imaged galaxy candidate at z ~ 10
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1. Cluster mass models
A reminder: only about 5% of the “stuff” in the
universe (energy density) is composed of
matter we know and understand, like stars,
gas, and neutrinos.
Galaxy clusters are extremely massive (1014 M⊙
in stars, or, > 10 ⨉ the GDP of the USA, in $)
and dominated by dark matter.
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1. Cluster mass models
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Many multiply imaged lens arcs identified in the deep
Frontier Fields imaging of the Abell 2744 and MACS 0416
clusters
The arcs put strong constraints on the mass distribution in
the clusters (e.g., stars plus dark matter)
The total mass of the cluster constrained with a precision
of only a few percent!
The improved mass model also yields more reliable
determination of the magnification map, which is
necessary for interpreting the distant background galaxies
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1. Cluster mass models
Jauzac et al. (2014)
Dozens of multiple
image pairs
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1. Cluster mass models
Jauzac et al. (2014)
Dozens of multiple
image pairs
Magnification
map
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2. “Ghost light” of shredded cluster galaxies
Trujillo et al. (2014)
Galaxy clusters are a violent
environment, with galaxies
rushing around at thousands
of kilometers per second.
Cluster galaxies can get
shredded in the process,
with the stellar remains
strewn about the cluster
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3. Dozens of galaxies at z > 7
Ishikagi et al. (2014)
Atek et al. (2014), Zheng et al. (2014)
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3. Dozens of galaxies at z > 7
Ishikagi et al. (2014)
Atek et al. (2014), Zheng et al. (2014)
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4. A multiply-imaged galaxy at z~10
a
b
c
Zitrin et al. (2010)
Detections only in the reddest
HST infrared filters suggest a
redshift of z~10.
a b
c
Detecting multiple lensed images
greatly increases the likelihood
that the object is truly at high
redshift and not rather a nearby
interloper.
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4. A multiply-imaged galaxy at z~10
Such faint objects can only be detected in the
very long full Frontier Fields exposures!
An HST orbit
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4. A multiply-imaged galaxy at z~10
Such faint objects can only be detected in the
very long full Frontier Fields exposures!
a
b
1 orbit
2 orbits
8 orbits
24 orbits
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Working as a team
NASA’s
Great Observatories
Hubble Space Telescope
Spitzer Space Telescope
Chandra X-ray Observatory
W.M Keck Observatory (Mauna Kea, HI)
European Southern Observatory, Very Large Telescope (Cerro Paranal, Chile)
Gemini Observatory (Mauna Kea, HI, and Cerro Pachón, Chile)
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Many more exciting results to come!
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