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Hubble Science Briefing
Studying the First Galaxies with the Hubble and the Webb Space Telescopes Hubble Science Briefing April 7, 2011 Massimo Stiavelli Space Telescope Science Institute
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Modern Cosmology HST launch on Shuttle Discovery - 24 April Launch mass 25,500 lbs. Length: 42.5 ft (13 m) Diameter: 14 ft (4.2 m) at widest. Primary: 2.4 m dia. Orbit: Altitude: 330 nmi, 28.5 deg inclination. 94 min. period. This is first coupling of HST with the human Space Flight Program, delayed several years by the tragic loss of Challenger. After long years of development and advocacy by the scientific community, with Lyman Spitzer, Jr. and John Bahcall playing prominent roles in the scientific and political arenas, the ‘Large Space Telescope’, was launched. The HST program is a collaborative program between NASA and ESA, the European Space Agency. The telescope was named HST in honor of Edwin Hubble, the American astronomer who early in the 20th century discovered that the distance to many faint nebulae was well beyond our Milky Way—the universe was populated by enormous star systems, galaxies—and that these galaxies were receding from us and from each other, implying that the Universe is expanding. And he found that the rate at which galaxies recede from each other is proportional to their separation (Hubble’s Law). This revolution in our concept of the universe led to nearly a century of efforts to measure accurately that expansion rate (Hubble constant), which implied the lifetime for the Universe. One of the primary scientific objectives for the HST mission was to measure the current expansion rate to an accuracy of 10% or better (which has been done, and continues to be improved). Movie: Sequence 1b.mov, 18 sec, launch of HST 2
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The Universe at redshift ~1300
COBE satellite 3
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Perturbations 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. z=18 z=5.7 Computer simulations show the growth of structure z=1.4 z=0 4
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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 form at the intersection of filaments. 5
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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. 6
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REIONIZATION OF THE UNIVERSE
As we explore the Universe on these scales -- we are about to encounter DARK matter 7
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z~1300, Hydrogen recombines, CMBR “released”
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Spectra of distant QSOs tell us that there is no diffuse neutral Hydrogen.
few neutral hydrogen clouds many neutral hydrogen clouds 9
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Spectra of distant QSOs tell us that there is no diffuse neutral Hydrogen.
few neutral hydrogen clouds many neutral hydrogen clouds but no diffuse neutral hydrogen 10
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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” 11
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Here something reionizes Hydrogen
Hydrogen is ionized : we see radiation at 912 < < 1216 A in QSOs at z<6 Here something reionizes Hydrogen z~1300, Hydrogen recombines, CMBR “released” 12
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7% of the age of the Universe
“Dark ages” 7% of the age of the Universe first light sources Population III reionization of H reheating of IGM 13
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UDF Hubble Ultra Deep Field 14
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Galaxies at z>6 redshift out of the ACS filters
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Need IR observations Objects at z>7 are faint and relatively rare. We need a sensitive IR instrument : the IR channel of the Wide Field Camera 3. 16
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Galaxies remain in the WFC3 filters up to z~10
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Photo: Z. Levay 18
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NICMOS 72 orbits 19
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WFC3 16 orbits 20
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Initially 16 galaxies at z~7, 5 galaxies at z~8 (currently 100+ at z > 6)
z~8 galaxies, Bouwens et al. z~7 galaxies, Oesch et al. (see also Finkelstein et al. 2010, and others) 21
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What about z>8 ? Our team has detected one candidate at z=10
(Bouwens et al. 2011). 22
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What did we learn? We can say is that first galaxies are at z≥10.
The galaxies we see are capable of reionizing the Universe but we need a contribution from lower mass galaxies that we do not detect directly. The number density of galaxies above the WFC3 UDF limit is decreasing with redshift. 23
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THE FIRST GALAXIES As we explore the Universe on these scales -- we are about to encounter DARK matter 24
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Reionization vs First Galaxies
Reionization is not necessarily completed by the First Galaxies. However, the First Galaxies must have formed before the completion of reionization. 25
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Indication from 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. 26
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The James Webb Space Telescope
The James Webb Space Telescope was designed from the ground up to study high-z galaxies. Four science themes guided the design, two extragalactic and two galactic. The one most relevant for us is the End of the Dark Ages theme. End of the dark ages: First light Nature of reionization sources 27
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JWST Quick Facts 28 Quick Overview of the telescope
Organization Mission Lead: Goddard Space Flight Center International collaboration with ESA & CSA Prime Contractor: Northrop Grumman Space Technology Instruments: Near Infrared Camera (NIRCam) – Univ. of Arizona Near Infrared Spectrograph (NIRSpec) – ESA Mid-Infrared Instrument (MIRI) – JPL/ESA Fine Guidance Sensor (FGS) – CSA Operations: Space Telescope Science Institute (STScI) Quick Overview of the telescope Details in presentations across the week 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 201? 28
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6.5m James Webb Space Telescope
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JWST improves over Hubble’s resolution
The Hubble UDF (F105W, F105W, F160W) Simulated JWST Could also stress: 1.) Success of archives 2.) Prize postdoctoral fellowships – Hubble, Spitzer, Chandra, ?Webb? springboard for launching career in astronomy. 30
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31 HST/ACS Viz Viz J H JWST/NIRCam HST/NICMOS J H JWST/NIRCam
03/07/2010 31
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JWST-Spitzer image comparison
1’x1’ region in the UDF – 3.5 to 5.8 mm Spitzer, 25 hour per band (GOODS collaboration) JWST, 1000s per band (simulated) (simulation by S. Casertano) 32
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The James Webb & Hubble to same scale
Astronaut JWST is 7 tons and fits inside an Ariane V shroud This is enabled by: Ultra-lightweight optics (~20 kg/m2) Deployed, segmented primary Multi-layered, deployed sunshade L2 Orbit allowing open design/passive cooling 33
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JWST : Status 34 Quick Overview of the telescope
72% of the observatory mass is in fabrication All mirror segment have completed rough polish to 150nm 6 flight segment have been coated and are completed MIRI NIRSPEC NIRCam Quick Overview of the telescope Details in presentations across the week 34
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Sunshield: full scale membrane test
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Instrument Engineering, Verification and Development Models
NIRCam ETU undergoing I&T NIRSpec DM testing is Complete! FGS EM integration is complete MIRI VM testing is complete! 36
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ETU Instruments in the GSFC SSDIF
MIRI NIRSpec NIRCam FGS OSIM ISIM Structure 37
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NIRCam ETU ready for Cryo Vacuum Test
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FLIGHT NIRSpec 39
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NIRSpec first light 40
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Flight MIRI 41
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Gold Coated Mirror Assemblies
After coating, final steps for flight mirrors are 3 axis vibe + optical testing 42
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Cryo Cycle 5 at MSFC XRCF with Gold-Coated EDU
JWST_ISIM.Sep.MSR 43
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OTE Progress 44 Fine Steering Mirror - Coated
Backplane Center Sections – PF and Flight Backplane Support Frame – PF Aft Optics Bench for Cryo Test 12 containers store either an assembled PMSA, SMA EDU or TM Tertiary Mirror - Coated Primary Mirror EDU - Coated 44
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Optical End-to-End Test @ JSC
An idea of what’s left to do. The test that makes sure image quality is good. Test chamber at JSC. 65’ x 120’ outside. CoC test for all mirror segments. Autocollimator flat for partial aperture verification of end-end focussing. Verification of thermal predictions. Difficult and expensive and time-consuming and necessary according to the TAT. Verify Optical alignment; center of curvature, autocollimator flats Verify workmanship Thermal balance Chamber outside dimensions 65’ x 120’ 45 JWST
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Launch Configuration Plan is to fly JWST with an Ariane 5
• JWST is folded into stowed position to fit into the payload fairing of the Ariane V launch vehicle Long Fairing 17m Upper stage H155 Core stage P230 Solid Propellant booster Stowed Configuration Plan is to fly JWST with an Ariane 5 Contribution from our European Partner Fairing size requires deployment no matter what launcher 46
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Conclusions WFC3-IR has allowed us to begin studying galaxies at redshift up to 10. Progress on these objects is going to be slow because they are too faint for any existing telescope to take spectra and verify their redshift and measure their properties. The James Webb Space Telescope has the sensitivity required to study these objects (and even higher redshift ones). 47
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