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Massimo StiavelliSpace Telescope Science Institute
Studying the First Galaxies with the Hubble and the Webb Space Telescopes
Hubble Science Briefing
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Modern CosmologyModern Cosmology
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The Universe at redshift ~1300
The Universe at redshift ~1300
COBE satellite
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PerturbationsPerturbations
z=18
z=0
z=1.4
z=5.7
Redshift z : 1+z gives the ratio of the radius of the Universe today and that at a given epoch in the past .
It also gives the ratio of the wavelength we observe over the one that was
emitted.
Computer simulations show the growth of structure
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Growth of perturbations
Underdensities grow like miniature Universes. They expand becoming rounder. Overdensities collapse and can become flattened or filamentary. This is the origin of the filamentary structures seen in simulations. Galaxies form along filaments. Clusters of galaxies at the intersection of filaments.
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Growth of perturbations
From random initial conditions it is “easy” to study the evolution of dark matter through computer simulations. The reason is that dark matter interacts only by gravity.
It is much more difficult to study the evolution of ordinary matter (gas) since its interactions are much more complex. Thus the formation of stars and galaxies share the complexity of weather forecast.
We think the first galaxies form at a redshift between 6 and 15 but there are many uncertainties. Thus, the input from observations is essential.
REIONIZATION OF THE UNIVERSE
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Hydrogen is ionized : we see radiation at 912 < < 1216 A in QSOs at z<6
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few neutral hydrogen clouds
many neutral hydrogen clouds
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Hydrogen is ionized : we see radiation at 912 < < 1216 A in QSOs at z<6
z~1300, Hydrogen recombines, CMBR “released”
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Hydrogen is ionized : we see radiation at 912 < < 1216 A in QSOs at z<6
z~1300, Hydrogen recombines, CMBR “released”
Here something reionizes Hydrogen
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“Dark ages”7% of the age of the Universe
• first light sources• Population III • reionization of H• reheating of IGM
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End of Reionization
Extensive absorption at z~6 in the ultraviolet suggests that hydrogen is neutral.
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UDFUDF
Hubble Ultra Deep Field
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UDF CropUDF Crop
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Studying the sources responsible for reionization was the main goal of the Hubble Ultra Deep Field. Today we know more z=6 objects than we knew at z=4 ten years ago.
Ionizing flux from z=6 tantalizing close to what is needed for reionization but not quite enough. Possibilities:
– z=6 do the job because they are at very low metallicity and hence their stars are hotter and produce more UV light
– z=6 do the job because LF has many dwarf galaxies too faint to be seen in the HUDF
– z=6 don’t do the job alone look at z=7+
Reionization
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Possible deficit of z>7 galaxies
The Luminosity Function (LF) is defined as the number density of objects (galaxies, stars) with a given luminosity.
The analysis of all deep fields observed with Hubble, finds evidence for a rapid change in the Luminosity Function of galaxies going from 6 to 7+. The significance is not very high due to small number statistics.
However, if this result is confirmed it would imply that reionization is indeed completed between 6 and 7 and that some combination low metallicity and a dwarf-rich LF does the job.
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Some examples
HST NICMOS HST ACS
<-- Probably not real
3 candidates
Detected in the IR but not in the visible
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Future Hubble observations
Objects at z>7 are faint and relatively rare. In order to obtain a significant sample we need a better instrument : the IR channel of the Wide Field Camera 3 which was installed on Hubble in May during Servicing Mission 4.
WFC3/IR can cover the same area as NICMOS Cam3 to the same depth in one tenth of the time.
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Hubble Ultra Deep Field 2009
Our group has been awarded a total of 336 HST orbits to study the population of galaxies at redshift 7 or higher using the WFC3. Most of these orbits will be spent revisiting the original HUDF and the first followup (HUDF05).
= NICP12
= NICP34
THE FIRST GALAXIES
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Reionization vs First GalaxiesReionization vs First Galaxies
Reionization is not necessarily completed by the First Galaxies. However, the First Galaxies must have formed before the completion of reionization.
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Indication from observationsIndication from observations
Above a redshift of 5, as the redshift increases galaxies seems to become fainter and rarer.
Number evolution
z=4z=5z=6z=7
Luminosity evolution
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Indication from theoryIndication from theory
The observed trend are in good agreement with the expectations with theory.
Models predict that the first galaxies might form around redshift 15 but they will be faint and rare. Thus, they might be outside the capability of Hubble.
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Cooling
In our everyday experience cooling generally occurs by thermal conduction to a colder object. Heat flows from the warm to the cold object and the warm object cools.
However, an object can cool radiatively, emitting light (e.g. infrared light). In our homes normal light bulbs cool radiatively. The filament heats because of its resistivity to an electric current and cools radiatively. Indeed, the filament is in vacuum (otherwise it would burn).
Thus, unlike thermal conduction, radiative cooling can happen in vacuum and is the most important cooling mechanism in space. Gas that is enriched with metal is a more effective coolant.
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A star is bornA star is born
Density and temperature of gas around a first star. From left to right the images refer to a time 0, 1, 2.7, and 8 Myrs after its formation.
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Paving the way for the first galaxies
Paving the way for the first galaxies
The first stars will enrich the Universe with heavier chemical elements (“metals”) and will produce the first black holes.
After the first and possibly second generation of stars gas in the Universe begins to have metallicities different from primordial. The additional metals change the way gas cools and make the formation of smaller mass stars easier.
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When stars fuse hydrogen into heavier elements, they produce both energy and metals.
When stars fuse hydrogen into heavier elements, they produce both energy and metals.
The role of metallicity
The first stars have practically no metals but during their lifetime they produce metals. Some end their life as black holes others undergo a supernova explosion and enrich the Universe with metals.
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Early in the life of the Universe when only few generations of stars had been formed the metallicity was very low.
Early in the life of the Universe when only few generations of stars had been formed the metallicity was very low.
Each generation of stars incorporates metals produced by the previous generations. Once the metallicity is high enough stars form as in the Milky Way.
Now High-z
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If we assume that stars formed at a constant rate over the lifetime of the Universe, there were at z=6 only 7 per cent or less of the stars we see today. Thus, the mean metallicity of the Universe was also likely (much) less than 7 per cent of the present value.
If we assume that stars formed at a constant rate over the lifetime of the Universe, there were at z=6 only 7 per cent or less of the stars we see today. Thus, the mean metallicity of the Universe was also likely (much) less than 7 per cent of the present value.
Now z=6
Age is only 7 per cent
of present age
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Metal poor stars are hotter and may have very different properties from present day stars.
Metal poor stars are hotter and may have very different properties from present day stars.
Detecting individual primordial stars is going to be very hard but it will be possible to detect primordial galaxies.
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The First Galaxies might have higher metallicity if thet are formed from enriched gas.
The First Galaxies might have higher metallicity if thet are formed from enriched gas.
Primordial stars? Stars enriched by a SN?
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JWST: Quick FactsJWST: Quick Facts
Description• Deployable cryogenic telescope - 6.5 meter ø, segmented adjustable primary mirror • Launch on an ESA-supplied Ariane 5 to Sun-Earth L2 • 5-year science mission (10-year goal): launch 2013
OrganizationMission Lead: Goddard Space Flight CenterInternational collaboration with ESA & CSA Prime Contractor: Northrop Grumman Space TechnologyInstruments: Near Infrared Camera (NIRCam) – Univ. of ArizonaNear Infrared Spectrograph (NIRSpec) – ESAMid-Infrared Instrument (MIRI) – JPL/ESAFine Guidance Sensor (FGS) – CSAOperations: Space Telescope Science Institute (STScI)
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JWST Science ThemesJWST Science Themes
Patchy Absorption
Redshift
Wavelength Wavelength Wavelength
Lyman Forest Absorption
Black Gunn-Peterson trough
z<zi
z~zi z>zi
Neutral IGM
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What are the first galaxies?When did reionization occur?
– Once or twice?
What sources caused reionization?
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JWST Science ThemesJWST Science Themes
Where and when did the Hubble Sequence form?
How did the heavy elements form?
Can we test hierarchical formation and global scaling relations?
What about ultraluminous infrared galaxies and active galactic nuclei?
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JWST Science ThemesJWST Science Themes
The Eagle Nebulaas seen in the infrared
How do clouds collapse?How does environment affect star-formation?
– Vice-versa?
What is the low-mass initial mass function?
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JWST Science ThemesJWST Science Themes
Fomalhaut (SST): Stapelfeldt et al 2004
Fomalhaut (ACS): Kalas, Graham & Clampin 2005
How do planets form?How are circumstellar disks like our Solar System?How are habitable zones established?
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6.5m James Webb Space Telescope6.5m James Webb Space Telescope
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z = 0.0 – 0.5
Probing the Early Universe in the Infrared with a 6m Space Telescope
Probing the Early Universe in the Infrared with a 6m Space Telescope
z = 0.5 – 1.6z = 1.6 – 6.0
z = 1.6 – 6.0 JWST simulation, 10,000 seconds per infrared band, 2.2m, 3.5m, 5.8m
1,000,000 seconds integration with HST
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JWST-Spitzer image comparison
JWST-Spitzer image comparison
Spitzer, 25 hour per band (GOODS collaboration)
1’x1’ region in the UDF – 3.5 to 5.8 m
JWST, 1000s per band (simulated)(simulation by S. Casertano)
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The James Webb & Hubble to same scaleThe James Webb & Hubble to same scale
JWST is 7 tons and fits inside an Ariane V shroudThis is enabled by:
• Ultra-lightweight optics (~20 kg/m2)• Deployed, segmented primary• Multi-layered, deployed sunshade• L2 Orbit allowing open design/passive cooling
Astronaut
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PMSA #13 (8 / A3 / A3) PMSA #18 (21 / C6 / C6) PMSA #17 (23 / B8 / B8) PMSA #16 (19 / A6 / A6) PMSA #15 (18 / C5 / C5) PMSA #14 (22 / B7 / B7)
PMSA #7 (13 / A4 / A4) PMSA #12 (15 / C4 / C4) PMSA #11 (20 / B6 / B6) PMSA #10 (16 / A5 / A5) PMSA #9 (4 / C1 / C1) PMSA #8 (17 / B5 / B5)
PMSA #1 (EDU-A / A1 / A1) PMSA #5 (6 / B2 / B2) PMSA #6 (7 / C2 / C2)PMSA #3 (12 / C3 / C3) PMSA #4 (5 / A2 / A2) PMSA #2 (11 / B3 / B3)
Flight PM, SM and TM Segments Received and are in process at Tinsley
Flight PM, SM and TM Segments Received and are in process at Tinsley
PM EDU (EDU-B / EDU / EDU) PM PFL-C (24 / C7 / C7) SM PFL (SM2 / SM1 / SM1) SM Flight (SM1 / SM2 / SM2) TM Flight (TM1 / TM1 / TM1)
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EDU Mirror - Figuring Process Pathfinder EDU Mirror - Figuring Process Pathfinder
Today
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
Concept Development Design, Fabrication, Assembly and Test
FormulationAuthorization
NAR (Program Commitment) Launch
science operations ...
ICR[Long Lead Approval]
Phase A Phase B Phase C/D Phase E
Formulation Implementation …
T-NAR
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SunshieldSunshield
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Technology Milestones metTechnology Milestones met
Near Infrared DetectorsApril 2006
Primary Mirror Segment Assembly
June 2006
Cryo ASICsAugust 2006
Microshutter ArraysAugust 2006
Heat SwitchesSeptember 2006
Large Precision Cryogenic StructureNovember 2006
Wavefront Sensing & ControlDecember 2006
CryocoolerDecember 2006
✔
Sunshield MaterialApril 2005
Mid-IR DetectorsJuly 2005
✔ ✔✔
✔
✔
✔
✔✔
✔
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Space science infrastructure and facilities only astronomers need
Space science infrastructure and facilities only astronomers need
Tinsley Large Optics Facility for JWSTTinsley Large Optics Facility for JWSTChandra’s X-Ray (cryogenic) calibration facility
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Hardware progressHardware progress
JWST_ISIM.May.QSR/48
Optical Telescope Element
Sun ShieldSpacecraft Bus
Integrated SI Module
Thermal model test
Model for membrane management tests
Engineering Segment and Flight Segment
Engineering Development Unit
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Launch ConfigurationLaunch Configuration
LongFairing17m
Upper stage
H155 Core stage
P230 SolidPropellantbooster
Stowed Configuration
• JWST is folded into stowed position to fit into the payload fairing of the Ariane V launch vehicle
